Cupped Fringe Lichen (Heterodermia hypoleuca): COSEWIC assessment and status report 2025

Official title: COSEWIC Assessment and Status Report on the Cupped Fringe Lichen (Heterodermia hypoleuca) in Canada

Committee on the status of Endangered Wildlife in Canada (COSEWIC)

Endangered 2025

COSEWIC assessment summary

Assessment summary – May 2025

Common name: Cupped Fringe Lichen

Scientific name: Heterodermia hypoleuca

Status: Endangered

Reason for designation: This rare arboreal lichen occurs in southern Canada in the provinces of Ontario, Quebec, and New Brunswick, and is closely associated with the alkaline bark of several broadleaf tree species, including ashes, elms, maples, and oaks. Ash trees in humid forests, its preferred habitat, are suffering from severe mortality associated with a non-native insect, the Emerald Ash Borer. As a result, there is a past and future decline of this lichen reducing the size of the population by more than 70% over the next three generations.

Occurrence: Ontario, Quebec, New Brunswick

Status history: Designated Endangered in May 2025.

COSEWIC executive summary

Cupped Fringe Lichen

Heterodermia hypoleuca

Wildlife species description and significance

The Cupped Fringe Lichen, Heterodermia hypoleuca, is a leafy lichen that grows in grey to blue-grey rosettes, usually to 10 cm in size, though it can occasionally reach up to 25 cm across. It typically grows on the trunks of mature hardwood trees. The rosettes are made up of 1 to 3 mm wide-branching lobes that are loosely attached to tree bark by a network of pale to dark root-like structures (rhizines) that cover the white undersides of the lichen. The fruit bodies (apothecia) on the upper surface are typically cup-shaped, with abundant marginal lobules.

Aboriginal (Indigenous) knowledge

All species are significant, interconnected, and interrelated. There is no species-specific Aboriginal Traditional Knowledge (ATK) in the report.

Distribution

The Cupped Fringe Lichen is a temperate to subtropical species with a widely disjunct global distribution. It is found throughout portions of eastern and western North America, as well as low-lying and montane regions of Central and South America, Africa, and eastern Asia. In the United States, it ranges mainly from the Appalachian Mountains west to the Ozark Ecoregion and north to the Great Lakes Basin. In Canada, the species occurs at its northern limit in portions of Ontario, Quebec, and New Brunswick.

Habitat

The Cupped Fringe Lichen is entirely dependent on the host trees on which it grows. In Canada, these are usually large, long-lived hardwood species in areas with productive, mature hardwood forests that overlay circum-neutral to alkaline substrates. Individuals occur on the trunks (and rarely the thick branches) of living trees, from a few centimetres above the ground up to at least 10 metres, though they most commonly occur between 1 and about 5 metres. Ash trees are the primary host substrate, supporting 74% of the population, followed by oak trees, which host 21%. Habitat includes humid, mature to old calcareous swamps, hardwood forests with vernal ponds or areas with persistent standing water, and rarely, Bur Oak alvar savannah near the Great Lakes coasts.

Biology

The Cupped Fringe Lichen can reproduce in two ways: sexually, through ascospores, or asexually, by breaking apart and growing from fragments. The ascospores, which contain only fungal DNA, are released from the fruiting bodies (apothecia) and are carried by wind, water, and animals. If the conditions are right, the ascospores grow fungal strands (hyphae). For a new lichen to form, these fungal strands must encounter a compatible green alga on a suitable bark surface. If the habitat and conditions are suitable, the fungal strands surround the alga and, along with other microorganisms such as bacteria and other fungi, grow together to create a new lichen.

Population sizes and trends

The enumerated Canadian population identified by field sampling is 476 thalli on 144 trees. For the assessment, we use the number of host trees as individual equivalents. A total of 46 subpopulations have been documented, 36 of which are considered extant. Of these, 34 are in Ontario, 1 is in Quebec, and 1 is in New Brunswick. About 98% of mature individuals occur in Ontario, 2% in Quebec, and less than 1% in New Brunswick. A 21% decline in mature individuals and a 35% decline in host trees is expected within five years, where thalli and dead host trees will be lost as bark substrates deteriorate. Over the next three generations (30 to 90 years), a 78% decline in mature thalli and a 74% decline of host trees (individual equivalents) is projected due to host tree mortality. The estimated Canadian population is likely higher than current counts suggest. Estimates suggest there could be an additional 580 to 900 thalli on 190 to 270 ash trees (individual equivalents) on private land between Peterborough and the Ottawa River, extending north to Pembroke. However, mortality rates for these individuals would likely near 100% within three generations.

Threats and limiting factors

The overall threat impact to the survival of the Cupped Fringe Lichen was assessed as Very high – High. The species is completely dependent on its host trees for continued survival. A total of 107 ash trees sustaining 351 mature individuals will be lost due to the impacts of Emerald Ash Borer (EAB), representing a 72% loss of all occupied host trees and a 74% decline in the number of mature individuals. Only five extant subpopulations occur exclusively on non-ash substrates and are not threatened by EAB. Logging and wood harvesting, road construction, and drought and severe storms caused by climate change are other significant threats.

Protection, status, and ranks

The Cupped Fringe Lichen has a global rank of G5 (Secure). It has a national rank and General Status rank of N3 (Vulnerable) in Canada, which will likely change to N2 following a current revision in Quebec. The Natural Heritage Information Centre (Ontario) has assigned the species a rank of S2 (Imperiled), and the Quebec Conservation Data Centre has assigned it a rank of S3 (Vulnerable); however, it is being revised to S1–S2. It is not yet ranked in New Brunswick. It is not explicitly protected by any federal or provincial laws, nor by any international agreements or conventions. Thirteen extant subpopulations occur in provincial parks and conservation reserves, or in privately owned/managed protected areas.

Technical summary

Heterodermia hypoleuca

Cupped Fringe Lichen

Hétérodermie à dessous blanchâtre

Range of occurrence in Canada (province/territory/ocean): Ontario, Quebec, New Brunswick

Demographic information

Generation time (usually average age of parents in the population; indicate if another method of estimating generation time indicated in the IUCN guidelines (2011) is being used)

Unknown, but estimated to be between 10 and 30 years based on other well-characterized lichen species found on stable bark substratum of mature/long-lived hardwood trees.

Is there an [observed, inferred, or projected] continuing decline in number of mature individuals?

Yes, observed and inferred. Observed declines from Emerald Ash Borer (EAB) and storm events causing windthrow killing occupied trees. Inferred due to continuing host tree mortality from EAB.

Estimated percent of continuing decline in total number of mature individuals within [5 years or 2 generations, whichever is longer up to a maximum of 100 years].

No. Not estimated over two generations.

[Observed, estimated, inferred, or suspected] percent [reduction or increase] in total number of mature individuals over the last [10 years, or 3 generations, whichever is longer up to a maximum of 100 years].

A 4% observed reduction in the number of mature individuals based on declines at three subpopulations totalling at least 20 thalli (on dead, downed trees at three confirmed subpopulations, possibly at a fourth based on dead trees observed from roadside). The reductions are recent, over the last five years, not three generations.

[Projected or suspected] percent [reduction or increase] in total number of mature individuals over the next [10 years, or 3 generations, whichever is longer up to a maximum of 100 years].

Yes. A 74% decline (projected) over the next three generations based on the number of occupied trees (individual equivalents) (107) lost to EAB (101) or other causes (storm events or natural decay) (6).

[Observed, estimated, inferred, or suspected] percent [reduction or increase] in total number of mature individuals over any period [10 years, or 3 generations, whichever is longer up to a maximum of 100 years], including both the past and the future.

Yes. A 74% decline (inferred) based on the number of occupied trees (individual equivalents) lost to EAB (107) or other causes (storm events or natural decay) (6) over the next three generations at extant subpopulations and a 4% past (recent) decline.

Are the causes of the decline a. clearly reversible and b. understood and c. ceased?

1. No, decline not clearly reversible if EAB persists and continues to spread
2. Yes, cause of decline understood
3. No, decline not ceased

Are there extreme fluctuations in number of mature individuals?

No

Extent and occupancy information

Estimated extent of occurrence (EOO)

127,452 km²

Index of area of occupancy (IAO)

(Always report 2 × 2 grid value).

180 km²

Is the population “severely fragmented” that is, is >50% of its total area of occupancy in habitat patches that are (a) smaller than would be required to support a viable population, and (b) separated from other habitat patches by a distance larger than the species can be expected to disperse?

Likely no, but unknown because the size of habitat patches needed to support a viable population of this species has not been determined.

Unknown

Number of “locations” (use plausible range to reflect uncertainty if appropriate)

There are six locations: one location represents 31 extant subpopulations with the most plausible threat from EAB; the remaining 5 extant subpopulations face impacts from climate change, but are treated separately since those effects are likely to be site-specific.

Is there an [observed, inferred, or projected] decline in extent of occurrence?

Yes, projected loss of 25 subpopulations where individuals occur exclusively on ash trees that will be lost due to indirect mortality via EAB (EAB was observed already at 14 of these).

Is there an [observed, inferred, or projected] decline in index of area of occupancy?

Yes, projected loss of 25 subpopulations and 107 occupied trees where individuals occur exclusively on ash trees expected to die due to indirect mortality via EAB (EAB was observed already at 14 of these).

Is there an [observed, inferred, or projected] decline in number of subpopulations?

Yes, projected loss of 25 of 36 extant subpopulations where all individuals occur exclusively on ash trees that will succumb to EAB (EAB was observed already at 14 of these 25).

Is there an [observed, inferred, or projected] decline in number of “locations”?

No

Is there an [observed, inferred, or projected] decline in [area, extent and/or quality] of habitat?

Yes, observed decline in area and quality of habitat at 14 subpopulations where the quality and extent of swamp forest with mature ash is declining due to EAB as large diameter/mature ashes (preferred substrate) aren’t being replaced. Projected for another 15 subpopulations where ash is an important canopy component, and these habitats will continue to decline in quality with the loss of key host trees. Also, potentially suitable unoccupied habitat with ashes is declining, limiting dispersal potential.

Are there extreme fluctuations in number of subpopulations?

No

Are there extreme fluctuations in number of “locations”?

No

Are there extreme fluctuations in extent of occurrence?

No

Are there extreme fluctuations in index of area of occupancy?

No

Quantitative analysis

Is the probability of extinction in the wild at least [20% within 20 years or 5 generations whichever is longer up to a maximum of 100 years, or 10% within 100 years]?

Not assessed

Threats (direct, from highest impact to least, as per IUCN Threats Calculator)

Was a threats calculator completed for this species?

Yes (Appendix 3).

Overall assigned threat impact: Very high – High

1. Natural system modifications (7.3 Other ecosystem modifications) Very high – High Impact
2. Climate change and severe weather (11.1 Habitat shifting and alteration) Unknown Impact (11.2 Droughts) Unknown Impact (11.4 Storms and flooding) High – Low Impact
3. Biological resource use (5.3 Logging and wood harvesting) Medium – Low Impact
4. Transportation and service corridors (4.1 Roads and railroads) Low Impact
5. Pollution (9.5 Air-borne pollutants) Unknown Impact

Rescue effect (immigration from outside Canada)

Status of outside population(s) most likely to provide immigrants to Canada.

Not ranked (that is, SNR or no rank) in any adjacent U.S. jurisdictions. However, Maine, Michigan, New York, Pennsylvania, and Vermont have only historical collections (none from the last 20 years). Minnesota has four recent collections from three sites. Ohio has one recent collection from 2017.

Is immigration known or possible?

Possibly, but unlikely because of distance. The closest extant site is in Ohio, over 600 km from the nearest Canadian site.

Would immigrants be adapted to survive in Canada?

Presumably.

Is there sufficient habitat for immigrants in Canada?

Unknown. It is unclear whether habitat is limiting in most of its range. However, it is highly unlikely to mitigate the ongoing impact of EAB.

Are conditions deteriorating in Canada?

Yes. Both the availability of its most important host trees (ashes) and the amount of swamp forest with mature ash is declining due to EAB, which is reducing substrate availability, and ashes are not reaching a suitable size rapidly enough to compensate for losses.

Are conditions for the source (that is, outside) population deteriorating?

Unknown. However, ashes face the same threat posed by EAB in adjacent jurisdictions in Maine, Michigan, Minnesota, New York, Ohio, Pennsylvania, and Vermont.

Is the Canadian population considered to be a sink?

No

Is rescue from outside populations likely?

No. Rescue is unlikely to change status because mature ash trees are dying due to EAB.

Data sensitive species

Is this a data sensitive species?

No

Status:

COSEWIC status history: Designated Endangered in May 2025.

Status and reasons for designation

Status: Endangered

Alpha-numeric codes: A3bce+4abce; C2a(i)

Reason for designation: This rare arboreal lichen occurs in southern Canada in the provinces of Ontario, Quebec, and New Brunswick, and is closely associated with the alkaline bark of several broadleaf tree species, including ashes, elms, maples, and oaks. Ash trees in humid forests, its preferred habitat, are suffering from severe mortality associated with a non-native insect, the Emerald Ash Borer. As a result, there is a past and future decline of this lichen reducing the size of the population by more than 70% over the next three generations.

Applicability of criteria

Criterion A (Decline in total number of mature individuals):

Meets Endangered, A3bce. Observed decline in number of mature individual equivalents that is projected to continue over the next three generations at a rate of 74%. Meets Endangered, A4abce, observed past decline of 4%, and future inferred and projected decline of mature individual equivalents at a rate of 74%. Most of the decline is due to the effects of an introduced insect species causing mortality of the preferred host trees.

Criterion B (Small range and decline or fluctuation):

Not applicable for Endangered. Meets Threatened, B2ab(i,ii,iii,iv,v). IAO is 180 km². The population is (a) known to occur from fewer than 10 locations, and (b) has a projected continuing decline in (i) EOO, (ii) IAO, (iv) number of sub-populations; an observed and projected continuing decline in (iii) quality of habitat; and observed and inferred continuing decline in (v) number of mature individual equivalents.

Criterion C (Small and declining number of mature individuals):

Meets Endangered, C2a(i). Number of mature individual equivalents is 334 to 414, with fewer than 250 in any one subpopulation, and there is an inferred continuing decline.

Criterion D (Very Small or restricted population):

Not applicable for Endangered. Meets Threatened, D1. Number of mature individual equivalents (334 to 414) is fewer than the threshold of 1,000.

Criterion E (Quantitative analysis):

Not applicable. Analysis not conducted.

COSEWIC history

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list. On June 5, 2003, the Species at Risk Act (SARA) was proclaimed. SARA establishes COSEWIC as an advisory body ensuring that species will continue to be assessed under a rigorous and independent scientific process.

COSEWIC mandate

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses the national status of wild species, subspecies, varieties, or other designatable units that are considered to be at risk in Canada. Designations are made on native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fishes, arthropods, molluscs, vascular plants, mosses, and lichens.

COSEWIC membership

COSEWIC comprises members from each provincial and territorial government wildlife agency, four federal entities (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biodiversity Information Partnership, chaired by the Canadian Museum of Nature), three non-government science members and the co-chairs of the species specialist subcommittees and the Aboriginal Traditional Knowledge subcommittee. The Committee meets to consider status reports on candidate species.

Definitions

(2025)

Wildlife Species

A species, subspecies, variety, or geographically or genetically distinct population of animal, plant or other organism, other than a bacterium or virus, that is wild by nature and is either native to Canada or has extended its range into Canada without human intervention and has been present in Canada for at least 50 years

Extinct (X)

A wildlife species that no longer exists

Extirpated (XT)

A wildlife species no longer existing in the wild in Canada but occurring elsewhere

Endangered (E)

A wildlife species facing imminent extirpation or extinction

Threatened (T)

A wildlife species is likely to become endangered if limiting factors are not reversed

Special Concern (SC)*

A wildlife species that may become a threatened or an endangered species because of a combination of biological characteristics and identified threats

Not at Risk (NAR)**

A wildlife species that has been evaluated and found to be not at risk of extinction given the current circumstances

Data Deficient (DD)***

A category that applies when the available information is insufficient (a) to resolve a species’ eligibility for assessment or (b) to permit an assessment of the species’ risk of extinction

*

Formerly described as “Vulnerable” from 1990 to 1999, or “Rare” prior to 1990

**

Formerly described as “Not In Any Category”, or “No Designation Required.”

***

Formerly described as “Indeterminate” from 1994 to 1999 or “ISIBD” (insufficient scientific information on which to base a designation) prior to 1994. Definition of the (DD) category revised in 2006

The Canadian Wildlife Service, Environment and Climate Change Canada, provides full administrative and financial support to the COSEWIC Secretariat.

Wildlife species description and significance

Name and classification

Scientific name: Heterodermia hypoleuca (Ach.) Trevis.

Pertinent synonyms: Anaptychia hypoleuca (Ach.) A. Massal., Parmelia speciosa var. hypoleuca Ach., Physcia hypoleuca Muhl. Tuckerm., Polyblastidium hypoleucum (Ach.) Kalb

Common names: Cupped Fringe Lichen, Hétérodermie à dessous blanchâtre

Family: Physciaceae

Major Group: Lichens (lichenized Ascomycetes)

Bibliographic citation: Atti Soc. Ital. Sci. Nat. Milano 11: 615. 1868 (1869)

Type: U.S. Pennsylvania, 29 November 1805, Muhlenberg (lectotype, selected by Moberg and Nash 1999: 5, H)

Heterodermia Trevis. is a genus of lichenized fungi in the family Physciaceae (Brodo et al. 2001) with approximately 175 species worldwide (Lücking et al. 2017). The species are most common in tropical montane regions, occurring mostly on tree bark.

The term hypoleuca comes from two Greek roots, hupo, “below,” and leukos, “white,” referring to the white undersides of the thallus lobes.

Mongkolsuk et al. (2015) attempted to split the monophyletic genus Heterodermia into several groups based on collections examined from Thailand, in which they formally described the genera Leucodermia Kalb and Polyblastidium Kalb based on terpenoid chemistry, overall thallus appearance, and anatomy, as well as two informally named species groups, but the phylogenetic position of the named or unnamed groups was not presented. The authors placed H. hypoleuca in Polyblastidium based on its non-ascending, foliose thallus, which attaches to the substrate, and on its ecorticate lower surface. Since a complete phylogeny of the genus is still lacking, the generic divisions proposed by those authors have not been widely accepted (for example, Fernanda de Souza et al. 2022) and North American species are, for now at least, retained within the genus Heterodermia sensu lato (Esslinger 2021).

Morphological description

Heterodermia hypoleuca is a spreading, loosely appressed foliose (leafy) lichen forming roundish patches (Figure 1), typically up to 10 cm wide. In the Canadian population, it has occasionally been observed to reach 25 cm, with linear lobes up to 3 mm wide, that are irregularly or dichotomously branched. Lobules resembling small versions of the primary lobes can develop in older central or damaged portions of the thallus, and these individuals often lack apothecia. The upper surface is mineral grey to blue-grey, smooth and epruinose, often with pycnidia, and the medulla is white. The lower surface is pale, white to tan (often darker towards the centre), and ecorticate (lacking a cortex), with dark, simple to squarrose rhizines coalescing into a mat and projecting marginally. Round apothecia (fruit bodies) <1 to 10 mm in diameter are produced on the lobe surface, and are strongly concave, with brown, non-pruinose discs and thick, in-rolled, lobulate thalline margins. Ascospores are brown, 2-celled, ellipsoid, Pachysporaria-type, measuring on average 23.5 to 30.5 µm × 12.5 to 16.0 µm (Moberg and Nash 1999).

Figure 1. Photographs of Heterodermia hypoleuca from Ontario. A) Overall habit, showing several thalli with apothecia growing on Green Ash bark. B) Closeup of apothecia showing distinctive lobed or “fringed” margins. C) A densely lobulate, merged thallus with many overlapping lobules and no apothecia on Green Ash bark (photos: S. Brinker).

Heterodermia hypoleuca is the only apotheciate species in the genus with non–ascending lobes known to occur in eastern North America (Lendemer 2009).

The photosynthetic partner in H. hypoleuca is a green unicellular coccoid alga in the genus Trebouxia, a very common lichen photobiont partner genus.

Chemistry

The chemical substances present in H. hypoleuca are atranorin, zeorin, and leucotylin.

Population spatial structure and variability

Little is known about the population structure and its variability in H. hypoleuca, but dispersal is likely limited. Individuals in the Canadian population typically occur along meandering river corridors or edges of forested vernal ponds or large wetlands surrounded by rich lowland forest. These environs likely have had less disturbance and logging pressure, being too wet/hazardous or inaccessible, and often contain larger and/or older trees relative to most surrounding forest stands. These sites also appear to be limited in extent and spatially restricted within the larger landscape matrix. The landscape surrounding occupied habitat is most often characterized by younger, even-aged forests; forests without appropriate tree hosts; forests occurring on noncalcareous parent or till material; or forests in drier, less humid upland habitats.

For the purposes of the report, occupied sites separated by at least 1 km, and up to 3 km in areas of continuous forest cover with persistently suitable habitat, have been treated as discrete subpopulations following the guidelines in NatureServe (2020).

Designatable units

There is no evidence for discreteness within the species’ Canadian range. No recognized infraspecific taxa or varieties of H. hypoleuca exist. Genetic diversity in H. hypoleuca has not been sufficiently studied to suggest or refute distinctiveness in any one region. The Canadian population of H. hypoleuca occurs in three COSEWIC National Ecological Areas (Great Lakes Plain, Boreal, Atlantic) (Figure 2), although natural disjunction between these is not sufficient to warrant separate designatable units.

Figure 2. Map of extant Heterodermia hypoleuca subpopulations (white circles ◯) in Canada (excluding extirpated subpopulations and historical collections with vague or questionable localities) used to determine the extent of occurrence (grey polygon) in relation to National Ecological Areas (EAs; Atlantic, Boreal, and Great Lakes Plains).

Special significance

Heterodermia hypoleuca appears to be a good indicator of mature, productive, “high quality” hardwood forests within its Canadian range. Most recent observations tend to occur in habitat that contains older and larger trees than the surrounding environs, and typically show fewer signs of human disturbance. This is a declining ecosystem in the northeast (for example, Hagan and Whitman 2004).

Aboriginal (Indigenous) knowledge

Aboriginal Traditional Knowledge (ATK) is relationship-based. It involves information on ecological relationships between humans and their environment, including characteristics of species, habitats, and locations. Laws and protocols for human relationships with the environment are passed on through teachings and stories, and Indigenous languages, and can be based on long-term observations. Place names provide information about harvesting areas, ecological processes, spiritual significance or the products of harvest. ATK can identify life history characteristics of a species or distinct differences between similar species.

Cultural significance to Indigenous peoples

There is no species-specific ATK in the report. However, H. hypoleuca is important to Indigenous Peoples who recognize the interrelationships of all species within ecosystems.

Distribution

Global range

Heterodermia hypoleuca occurs in temperate to subtropical humid forests and woodlands. It has a disjunct global distribution and is found in montane regions of Central and South America, eastern and southern Africa, Australia, and eastern Asia (Enkhtuya and Javkhlan 2019; Moberg 2011; Swinscow and Krog 1976).

In the United States, its range includes temperate areas of the Appalachian Mountains, extending west locally through the Ohio Valley to Minnesota and the Ozarks (Brodo et al. 2001) (Figure 3). In the northeast, records from New England are mostly historical with only two more recent collections from Maine (Hinds and Hinds 2007). It occurred historically on the eastern seaboard as far south as the Delmarva Peninsula but is considered extirpated in that region (Lendemer and Noell 2018). In the west, it occurs locally along the eastern border of the Sonoran Desert area and in the subtropical part of Baja California (Moberg and Nash 1999).

Figure 3. Distribution of Heterodermia hypoleuca in North America north of Mexico based on collections. Collections made prior to 2003 (>20 years old and considered historical) are indicated with a black circle (●). Early literature reports from Canada that are unverifiable are indicated with a black asterisk (✱). Collections made between 2003 and 2024 are indicated with a white circle (◯).

Canadian range

Heterodermia hypoleuca occurs in the provinces of Ontario, Quebec, and New Brunswick. It occupies portions of three of Canada’s terrestrial ecozones including the northern part of the Mixedwood Plains, the southern part of the Boreal Shield and a small area of the Atlantic Maritime (Wiken et al. 1996; Figure 2). It reaches its northern distributional limit in this region at 48.4° N. Its Canadian range likely accounts for less than 1% of its global range.

Ontario

In Ontario, there are 34 extant subpopulations representing 98% of the Canadian population, ranging from Peterborough County east to the Ottawa River. A single small outlying subpopulation occurs west of this area on Manitoulin Island. Five subpopulations here are considered extirpated (virtually no likelihood of rediscovery due to significant alteration from urbanization or intensive agriculture, and recent search efforts failed to locate individuals or suitable habitat), and one is possibly extirpated (has not been observed in >20 and the single individual was recorded on a downed tree, suggesting it is likely gone). Two other subpopulations are excluded because they are based on early literature reports and are of questionable validity (see Search effort).

Quebec

In Quebec, there is one extant subpopulation from the St. Armand area near the Vermont border representing 2% of the Canadian population. Another five historical collections are known from Gatineau east to Île Bonaventure. Their status has not been assessed in recent years, but their localities are vague and their continued presence is unknown. However, at least two thalli were recorded on elm trees which have suffered extensive declines due to Dutch Elm Disease and are likely extirpated.

New Brunswick

A small subpopulation in New Brunswick was recently discovered along the St. John River in 2022 (Clayden pers. comm. 2023), representing less than 1% of the Canadian population. There are no other confirmed records from other parts of Canada.

Extent of occurrence and area of occupancy

The extent of occurrence (EOO) is 127,452 km² calculated using a minimum convex polygon that encompasses records from 2012 to 2024 (Figure 2).

The index area of occupancy (IAO) is 180 km² calculated using a 2 × 2 km grid drawn over known records from 2012 to 2024.

Records that have vague locational information were only reported historically on dead trees, or are considered extirpated were excluded from these calculations.

Search effort

Ontario

Prior to 1998, H. hypoleuca was considered possibly extirpated in southern Ontario (Wong and Brodo 1992) and in Canada (Goward et al. 1998). Based on verified collections at the Canadian Museum of Nature (CANL), it was formerly present in several locations: Ottawa (Macoun, 1891), near Hull (Macoun, 1907), Brighton (Macoun, s.n.), Prescott (Billings, s.n.), and near Wooler (Macoun 1902). Lichenologists familiar with this lichen (Sam Brinker [SB], Irwin Brodo, Rob Lee [RL], James Lendemer, Chris Lewis [CL], Troy McMullin, and numerous others) have searched many lichen-rich sites in southern Ontario over the past 50 years, covering the range of these historical localities and expected habitat for the species. Dedicated searches of suitable swamp forest habitat were also completed during the preparation of the COSEWIC status report on Flooded Jellyskin (Leptogium rivulare) in Canada (COSEWIC 2015) by SB and CL. Other targeted searches for H. hypoleuca were carried out independently by SB and CL between 2012 and 2019. While no rediscoveries were made at historical locations, this work resulted in the discovery of ten new subpopulations from Peterborough, Hastings, Frontenac, and Renfrew counties (Brinker 2020; Lewis 2019; Lewis and Brinker 2017). Several detailed lichen-focused inventories have also been completed in southern and central Ontario without documenting additional records of H. hypoleuca (for example, Brodo et al. 2013, McMullin and Lendemer 2016, Maloles et al. 2018, Brodo et al. 2021). Between 2022 and 2024, Jon Ruddy (JR) independently searched for H. hypoleuca in eastern Ontario and discovered it in four new subpopulations (See Tables 1 and 2).

Macoun (1902) mentioned H. hypoleuca (as Physcia hypoleuca) from Algonquin Park (July 19, 1900, Red Pine Lake) and Lake Nipigon (July 17, 1884); however, there are no supporting specimens at CANL, where most of Macoun’s collections are housed. Additionally, there have been no subsequent reports from either region, though both areas have been surveyed by experienced lichenologists.

Areas of potential occurrence in the general vicinity of Lake Nipigon, where the lichen was reported by Macoun (1902), have been explored over many years by lichenologists. Ahti’s (1964) pioneering assessment of macrolichens in boreal and arctic portions of Ontario included numerous collection sites along the northern coastal strip of Lake Superior and areas of the Lake Nipigon basin (corresponding to his strongly humid southern boreal forest zone). However, he did not document H. hypoleuca. The area surrounding the city of Thunder Bay which is known for several disjunct stands of Acer saccharum has been well covered by Claude Garton and Paul Barclay-Estrup with respect to foliose and fruticose lichens, and neither documented any records of H. hypoleuca (Barclay-Estrup and Sims 1979, Crowe 1994). Crowe (1994) produced a list of lichens for the Thunder Bay District and did not make mention of H. hypoleuca. Sam Brinker explored numerous islands on Lake Nipigon in 2016 that contained mature cedar forests, and did not successfully locate any individuals. Sam Brinker also searched over 30 mature cedar and ash swamp forests in the Rainy River and Thunder Bay District in 2016 to 2017 during targeted surveys for Rimmed Shingle Lichen (Fuscopannaria leucosticta) (COSEWIC 2019). Numerous islands on the north shore of Lake Superior have been surveyed by SB with Parks Canada in the newly established Lake Superior National Marine Conservation Area, which included visits to numerous offshore islands in 2018 and 2019. The Tuckerman Group of lichenologists (over 40 attendees) visited Sleeping Giant Provincial Park in 2019 and conducted detailed lichen surveys throughout the park, including representative old-growth coastal forest stands and ash and cedar swamp forest, but did not record the species.

Areas of potential occurrence in and surrounding Algonquin Park have also been explored without documenting H. hypoleuca. Several lichen checklists for the park have been compiled from collecting activities of former park staff and CANL research associate staff spanning 50 years. The most recent lichen checklist produced in 2023 (Lewis et al. 2023) included focused surveys of unique habitats including old-growth dependent lichens in mature forest stands, and produced no records of H. hypoleuca. The lack of any substantiating observations casts some doubt about its historical presence here and at Lake Nipigon. These early reports may represent transcription or labelling errors, as both Wong and Brodo (1992) and others who have examined Macoun’s collections (for example, Godfrey 1977), have noted inconsistencies with his label data in his series of Canadian lichens. The overall scarcity of calcareous hardwood stands in Algonquin Park casts further doubt about its presence there.

Heterodermia hypoleuca occurs in Minnesota, but is very rare. There is a possibility that it could occur in adjacent areas of NW Ontario, particularly in the southern Rainy River District. In 2013, SB and CL conducted unsuccessful searches of its potential range in this region, including areas around Lake of the Woods, Rainy Lake, and Rainy River bordering Minnesota, while conducting targeted rare lichen surveys.

Quebec

Prior to recent search efforts, seven specimens representing six subpopulations from Quebec were housed in collections at the CANL, Louis-Marie Herbarium (QFA), and New York Botanical Gardens (NY). All but one were made before approximately 1970. The label data associated with these specimens are mostly vague, with only the nearest town or place name referenced, making relocation difficult. In 1905, John Macoun made three collections, including one from Montmorency Falls and two from “Cap-à-l’Aigle.” While multiple locations in Quebec share the name Cap-à-l’Aigle, Macoun made a collecting trip to the St. Lawrence River Valley in 1905 where he visited Cap-à-l’Aigle on July 25 (Lamb 1968), located on Rivière-Malbaie near its mouth on the St. Lawrence River, just north of Point-au-Pic.

There is a 1958 Fabius LeBlanc collection of H. hypoleuca from Mont Johnson (also known as Mont Saint-Grégoire), southeast of Montreal. There is also a specimen collected by Eric Thorn in 1961 from Île Bonaventure near Gaspé, and an undated Anne Hanes specimen from Gatineau Park. Hanes’ specimen was likely collected sometime between 1967 and 1973, based on a 2023 search of the Consortium of Lichen Herbaria (CLH), which produced 91 of her specimens from Gatineau Park, all made between these years. Despite considerable lichen exploration in the Ottawa and Hull regions by CANL staff and their students, from the 1970s to the present day (which included Gatineau Park), no recent observations of H. hypoleuca have been made in the region (Brodo 1981, 1988; Freebury 2011; Brodo et al. 2021). There was a study of the epiphytic lichens and bryophytes of hardwood forests in the Eastern Townships, but H. hypoleuca was not recorded (LeBlanc 1963). Other notable early lichen studies include surveys of areas between Quebec City and the Gaspé Peninsula (Lepage 1947 to 1949). More recently, researchers such as McMullin et al. (2017), Paquette (2019), and Paquette and McMullin (2020), have contributed to documenting lichen diversity in the Gaspé Peninsula and Côte-Nord, but did not report the presence of H. hypoleuca. Other targeted lichen surveys of southern Quebec in mixed and deciduous forests between the 45th and 50th parallels were recently summarized by Lavoie et al. (2024), which include the discovery of numerous rare lichens, though no new H. hypoleuca locations were documented (See Tables 1 and 2).

The only extant subpopulation that is known in Quebec was discovered by Richard Harris at Sanctuaire George H. Montgomery in 2016 during the 40th annual Andrews Foray (traditionally a bryophyte foray with lichenologists attending as well).

Two specimens collected by Frère Marie-Anselme in 1936 and 1938 from Shefford and Lac Sept-Îles, housed at QFA and originally identified as H. hypoleuca, represent misidentifications. These specimens are Heterodermia speciosa, powdered fringe lichen, and Anaptychia palmulata, shaggy-fringed lichen.

New Brunswick

In New Brunswick, H. hypoleuca was recently discovered by Stephen Clayden in April 2022 on a single multi-stemmed Green Ash (Fraxinus pennsylvanica) near the Saint John River at Lower Lincoln, about 15 km downriver from Fredericton. Its presence on the same tree was reconfirmed in April 2024, and approximately two hours of searching in the same area yielded no additional observations. No other targeted surveys for this lichen have been conducted in the province. However, Green Ash stands along or near the Saint John River between Mactaquac and Saint John have been examined sporadically during general lichen surveys over the past few decades and have not produced any other records of H. hypoleuca (Clayden pers. comm. 2024).

Manitoba

Reference to H. hypoleuca from Manitoba exists in an unpublished list of macrolichens prepared by Michele Piercey-Normore and reported by the Canadian Endangered Species Conservation Council (CESCC) (2010); however, its presence has proven to be incorrect. It was reported in error and the collection believed to be the basis of the report was revised to Heterodermia speciosa (Michele Piercey-Normore and Diana Sawatzky pers. comm. 2022).

Habitat

Habitat requirements

Heterodermia hypoleuca is entirely dependent on the host trees on which it grows. Its preferred substrate is the bark of long-lived hardwood trees that typically occur in mature, productive forests with high humidity and canopy gaps, and frequently with old and leaning trees that often have patchy bryophyte cover (Figure 5). Two subpopulations occur in unusual Bur Oak (Quercus macrocarpa) alvar savannah and another extends into open oak woods along the Ottawa River. At these locations there are numerous old oak trees that occur near large bodies of water, where high levels of constant humidity mimic conditions of humid swamp forests. Thalli colonize the vertical trunks (or rarely thick branches) of living trees from a few centimetres above ground up to at least 10 metres, though recent surveys found individuals to occur mostly at roughly breast height to about 5 metres. Thalli may persist on dead trees for a time, but eventually die as the bark decays or falls off. In a phytosociology study of corticolous cryptograms in Wisconsin, Hale (1955) found it to occur most frequently at 1.3 metres from the base of trees rather than on the base. Host tree trunks are typically clear of dense undergrowth, allowing for good air circulation and light penetration. During surveys between 2019 and 2024, it was observed that suitable host tree trunks that were shaded by dense shrubby undergrowth or were in stands that lacked canopy gaps were not colonized.

Heterodermia hypoleuca’s preferred substrata are trunks of medium- to large-sized hardwood trees with relatively thick, corky, and often fissured bark (Figure 6). These bark characteristics are likely important in retaining moisture and may also provide suitable microhabitat for the establishment of dispersing propagules. Bark chemistry plays an important role in controlling epiphytic lichen communities (Hauck 2011). Roughly 95% of all individuals in the Canadian population occur on ashes (Fraxinus spp.) and oaks (Quercus spp.); 90% of the host trees are ashes and oaks, species which tend to have a slightly basic bark pH, especially as they attain older ages (Farmer et al. 1991). Trees commonly encountered in occupied habitat with smooth or slightly acidic bark, such as Silver Maple (Acer saccharinum) or the hybrid Freeman’s Maple (Acer x freemanii), did not host H. hypoleuca thalli. While the connection between soil and bark chemistry is not proven, significant correlations between bark and soil chemistry suggest higher amounts of total bark calcium is positively correlated with soil pH (Gustafsson and Eriksson 1995). Calcium has also been considered to account for a large part of the buffering capacity and regulation of bark pH (Farmer et al. 1991). In its Canadian range, both tree species selection and underlying soil chemistry support this lichen’s affinity for base-rich substrates.

Occasionally, smaller trees are colonized, but normally within stands that contain larger trees surrounded by continuous forest cover. This suggests forest continuity (temporally unbroken continuity of forest stand habitat), rather than just tree age or size is likely important in determining habitat suitability (for example, Boch et al. 2013). It is unclear if bryophyte cover plays any positive role in the establishment or growth of H. hypoleuca. Thalli were occasionally observed adjacent or partially over bryophytes on tree trunks. More often; however, thalli were growing on bare bark. In some cases, occupied trees had luxuriant bryophyte growth elsewhere on the tree trunks, particularly in humid sites with mature, open canopies.

Table 3 presents the number of mature individuals on each host tree species. Of 476 individuals recorded, 351 (74%) occur on ash trees, including Green Ash (Fraxinus pennsylvanica), Black Ash (F. nigra), and unidentified ash species. Ninety-nine individuals (21%) occur on Bur Oak (Quercus macrocarpa) and Red Oak (Q. rubra), followed by 12 (3%) on American Basswood (Tilia americana), 10 (2%) on Sugar Maple (Acer saccharum), 3 (1%) on Eastern White Cedar (Thuja occidentalis), and one (<1%) on Bitternut Hickory (Carya cordiformis). Figure 7 provides a detailed breakdown of all living and dead host trees occupied by H. hypoleuca at extant subpopulations. Ashes are the most important host substrate, representing 70% of occupied trees. Bur Oak and Red Oak represent 19% of occupied trees, followed by American Basswood (4%), Sugar Maple (3%), Eastern White Cedar (2%) and Bitternut Hickory (<1%). Early collections suggest that additional substrates, such as American Elm (Ulmus americana), spruce (Picea sp.) and birch (Betula sp.) may have been historically occupied.

In adjacent jurisdictions to Canada, such as Wisconsin, habitat descriptions include coastal hardwood forests of southern Lake Superior with varying compositions of oak, maple, and birch, and maple, birch, and balsam fir (Wetmore 1990). In Minnesota, Wetmore (1981) mentioned it from “an old, dry ash bog that probably escaped logging.” In Ohio, only one recent collection has been made where H. hypoleuca occurred on the base of large oaks in mature forest (Curtis 2022 pers. comm.). Elsewhere in the U.S., recent observations, which primarily include areas of high-elevation forest in the Appalachian and Ozark Mountains, are usually associated with higher quality mature forest stands where the lichen mostly occurs on white oaks and other soft-barked trees like ashes (Lendemer pers. comm. 2021).

Habitat trends

A substantial portion of mature forest habitat in eastern North America, including the Canadian range of H. hypoleuca, has been lost since the arrival of Europeans (Fuller et al. 1998; Laflamme et al. 2016). Logging, forest fires, and settlement between the mid-1700s and the early 1900s resulted in the destruction of much of the original forests coinciding with the species range. The Great Lakes Plains National Ecological Area (Figure 2), where 20 of the 36 extant subpopulations representing 56% of the Canadian population of H. hypoleuca occurs, is the most anthropogenically modified region in Canada, having undergone dramatic change over the past 200 years. Forest was originally the dominant ecosystem type in most of the ecozone (Taylor et al. 2014). By 1920, about 90% of the original forests south and east of the Canadian Shield in Ontario were converted to non-forest uses (Larson et al.1999). While forest cover has rebounded since that time to roughly 22% to 25% today, the current landscape is heavily fragmented, and most forest remnants are even-aged second or third growth stands occurring in isolated patches (Taylor et al. 2014). It is estimated that less than 0.07% of the remaining woodlands in the mixedwood plains can be characterized as old-growth (based on a definition of greater than 120 years), which would have been dominant in the period prior to European settlement (Taylor et al. 2014).

Fifteen H. hypoleuca subpopulations representing 42% of the Canadian population fall within extreme southern portions of the Boreal Ecological Area, although these are all within 30 km or less of the Great Lakes Plains boundary to the south, where forests have generally been subject to the same pressures and changes.

One extant subpopulation occurs in the Atlantic Ecological Area. Historical accounts by early travellers in the Atlantic Maritime Ecozone of Quebec and New Brunswick described a different forest from what is encountered in much of the region today, with larger trees and higher proportions of late-successional species (Loo et al. 2010). The early 1800s saw the onset of major changes to forest cover with the start of commercial logging and the availability of an extensive network of rivers and tributaries to transport logs. Sequential waves of selective harvesting and clearcutting of more desirable shade-tolerant hardwoods through to the present day have caused large decreases in cedar, maple, beech, ash, and other tolerant hardwoods in these regions (Bouchard et al. 1989), thereby reducing the quality and extent of suitable habitat for H. hypoleuca. In their description of major forest types and their human influences, Loo et al. (2010) reported that wet calcareous mixedwood and rich tolerant bottomland forests in the region have been greatly reduced and highly fragmented due to clearing and draining for agriculture and urban development, flooding for power production, and removal of trees for timber extraction.

Biology

Life cycle and reproduction

Heterodermia hypoleuca produces apothecia and ascospores derived from meiosis that are expelled from the apothecia, representing propagation through fungal-only propagules. Conidia-bearing structures (pycnidia) are commonly observed on thalli and produce asexual spores that likely function primarily as sexual gametes involved in apothecia formation. However, conidia of a few lichen fungi have been successfully germinated in culture (for example, Vobis 1977), and it is possible that they might function in some cases as vegetative dispersal of the mycobiont. However, there are no records of H. hypoleuca conidia germinating. Because compatible photobiont cells are not dispersed together with ascospores, to germinate and give rise to a new individual, an ascospore must land on a suitable substratum hosting a compatible photosynthetic partner, an alga in the genus Trebouxia. If the photobiont strain and mycobiont partners are compatible, the alga will become enveloped by fungal hyphae and a lichen will begin to form and differentiate into a visible thallus. It is not known how long it takes H. hypoleuca to develop from a germinating ascospore to a reproductively mature thallus, nor is the lifespan known. Soredia, isidia, or other specialized vegetative propagules are lacking in H. hypoleuca. It likely therefore reproduces vegetatively through occasional fragmentation of the thallus, although it is not known how often this occurs or under what circumstances.

Generation time

Like other mature forest-dwelling macrolichens that do not produce specialized asexual reproductive structures containing both the mycobiont and photobiont (for example, Anzia colpodes), the generation time of H. hypoleuca has been estimated to be between 10 and 30 years (COSEWIC 2015). While the generation time of H. hypoleuca is unknown, this may be a reasonable estimate for this species based on other well-characterized lichen species found on stable bark substratum of mature/long-lived trees (for example, Larsson and Gauslaa 2011; Lättman et al. 2009). It may be possible for small fragments or lobules that break off the main thallus to reattach down and perhaps up occupied tree trunks transported by gravity, water flow or animal activity. In some sites little within-stand recruitment seems to occur, even where well-developed thalli are present. This could reflect low rates of successful thallus fragmentation and recolonization, successful re-establishment via ascospores, or both.

Physiology and adaptability

Little is known about the physiology of H. hypoleuca in experimental or quantitative studies. Its requirements can be inferred to some degree from its geographic range and within-site distribution. It is completely dependent on other taxa (host tree substratum) for its survival. Its restriction to certain host tree species suggests a preference for bark with a good moisture-holding capacity, and with a relatively high pH and calcium content. These conditions seem best developed in areas on the landscape where trees occur over base-rich soils or parent material. Areas dominated by acidic bedrock or other non-calcareous soils, or trees with acidic bark do not seem to provide habitat for H. hypoleuca in Canada.

Its preference for wet forests that are flooded for a portion of the year or occur near open water in Canada suggests a need for high relative humidity. Its tendency to grow on tree trunks near water features that produce canopy gaps also indicates a preference for higher light levels than those in closed-canopy forests.

Lobules sometimes present on the thallus surface have a possible role in reproduction and dispersal (synonymous with thallus fragmentation), although this has not been proven. Rather, in lichens that form them, it may serve to increase the surface area and boundary layer for gas exchange and water relations (Ott et al. 1993; Tretiach et al. 2005).

Dispersal and migration

Under suitable conditions, H. hypoleuca thalli produce apothecia which contain ascospores. Once mature, the asci eject the ascospores where they disperse passively by wind providing opportunity to colonize new habitat. It is not known how far spores of H. hypoleuca travel (particularly through fragmented habitats), or how long they survive aloft given the difficulties of direct observation. Studies of deposition in other taxa suggest spore deposition drops off to near zero over several metres (for example, Lönnell et al. 2012), although Ronnås et al. (2017) provide evidence to the contrary for lichen-forming fungi. They show that effective ascospore dispersal can be several hundred to thousands of metres from paternal individuals. Ascospores are much more likely to travel longer distances than larger thallus fragments, but that does not guarantee their successful establishment and development. There are many establishment limitations of ascospores that prevent successful colonization of new trees. Suitable substrates, environmental conditions (light, temperature, humidity), and the presence of compatible photobionts are necessary once they come to rest following a dispersal event. Its absence from many areas of apparently suitable habitat is suggestive of rare instances of successful long-distance dispersal.

Because H. hypoleuca does not produce specialized asexual symbiotic propagules (for example, isidia, soredia, phyllidia, schizidia) its primary reproductive mode to colonize new unoccupied habitat is likely sexual reproduction via only the fungal partner. Larger propagules, such as thalli fragments (containing both fungal and algal cells), may detach and reattach elsewhere on the same tree trunk. While they are unlikely to disperse any measurable distance within suitable habitat beyond occupied trees, they have a higher potential for successful establishment than fungal-only ascospores (Tripp et al. 2016). Although not easily observable, the role of avian, arthropod, and mammalian vectors of ascospores, thallus fragments, or living cells of lichen-forming fungi and their photobionts is widely acknowledged and may play a role in the occasional movement propagules.

Interspecific interactions

No obligate associations are known for this species. Heterodermia hypoleuca is one of several hosts for the lichenicolous fungus Sphaerellothecium gallowayi (Diederich 2007). It produces black perithecia that develop over a superficial, dark mycelium obligatorily confined to species of Heterodermia. It has not been reported on North American material of H. hypoleuca (one record from Papua New Guinea).

Population sizes and trends

Sampling effort and methods

During the preparation of this status report, 30 subpopulations with H. hypoleuca records were assessed by Sam Brinker between 2019 and 2024. More than 60 additional sites (defined as a discrete sampling area separated by at least 1 kilometre) were also searched without locating any individuals. A summary of survey dates, sampling locations, and search result are provided in Table 1. Extirpated and excluded subpopulations (Table 2), those on private land, or with vague geographic details were not assessed. In all, search effort totalled over 275 person hours in southern, central, and northwestern Ontario, from Sarnia north to Lake Superior Provincial Park and Timiskaming, west to Rainy River District and Lake of the Woods (Figure 4). SB also visited two sites in Quebec in the vicinity of the only recently documented subpopulation near St. Armand, and a nearby site at Reserve Ecologique Marcel-Raymond. This survey effort resulted in the discovery of 20 new H. hypoleuca subpopulations. Surveys involved searching the following habitat types:

1. deciduous and mixed swamps, particularly along lakeshores or rivers
2. deciduous or mixed hardwood forests adjacent to large wetlands, bodies of water, or that contained vernal ponds with seasonally flooded treed areas in geographic regions with calcareous parent or till material
3. Oak savannah or woodland remnants near bodies of water

Figure 4. Search effort and locations of Heterodermia hypoleuca observations in Canada. White circles (◯) indicate recent records (made between the years 2003 to 2024). Black circles (●) represent historical records with focused search effort (pre-2003). Black triangles (▲) represent historical records lacking specific search effort. White circles with an x (⊗) represent unsuccessful searches completed during fieldwork for this report between the years 2019 to 2024. Half circles (◑) represent pre-2019 general search and collecting activity with respect to the lichen genus Heterodermia within the Canadian range of H. hypoleuca.

Figure 5. Photographs of various hardwood stands supporting habitat for Heterodermia hypoleuca in Canada. A) Mature deciduous hardwood forest with vernal pond in eastern Ontario. B) Deciduous swamp forest with occasional leaning trees in central Ontario. C) Rich lowland floodplain forest along the Ottawa River. D) Bur Oak alvar savannah along Lake Ontario (photos S. Brinker).

Figure 6. Photographs illustrating tree size and bark characteristics of occupied ash trees which host 74% of the Canadian population. A) Old, large-diameter Green Ash tree trunk occupied by Heterodermia hypoleuca at the edge of calcareous deciduous swamp surrounded by younger forest. B–C) Closeups of varying bark texture of large diameter occupied ash trees showing deeply furrowed, corky bark with patchy bryophyte cover (photos S. Brinker).

Surveys consisted of visually examining the trunks and large branches of suitable hardwood trees (at ground level, and aided with binoculars or DSLR camera with a 200 mm zoom lens) believed to have appropriate bark properties (see Habitat requirements), including ashes (Fraxinus nigra, F. pennsylvanica, F. americana), maples (specifically Acer saccharum, A. nigrum), oaks (Quercus macrocarpa, Q. rubra), American Elm (Ulmus americana), American Basswood (Tilia americana), Bitternut Hickory (Carya cordiformis), and Eastern White Cedar (Thuja occidentalis). Once found, counts of mature individuals included all thalli over 1 cm wide (large enough to confidently detect with distinct lobes) and were tallied along with the number of trees and tree species occupied, the number of thalli on dead standing and downed trees, and the presence of Emerald Ash Borer, (Table 4). Identifying individuals was sometimes difficult because thalli in this species can split or merge together, complicating efforts to accurately tally them. A voucher specimen was collected at most subpopulations if one did not exist, except where too few individuals were present. Those details and the presence/absence of apothecia by subpopulation is provided in Appendix 1.

Abundance

For this assessment, we use the number of host trees as individual equivalents. The main reason for this approach is that arboreal lichens that live on the bark of trees will not survive when the trees die. This brings better consistency with our assessments for the Mosses and Lichens Specialist Subcommittee (M&L SSC) and is also better aligned with published recommendations made to the International Union for Conservation of Nature (IUCN) (Bergamini et al. 2019; Yarh et al. 2024). For transparency and ease of comparison with previous COSEWIC reports as well as the scientific literature, we still report on the number of lichen thalli.

Based on survey data collected between 2012 and 2024, the Canadian population consists of 476 mature thalli distributed among 144 trees at 36 extant subpopulations. Since H. hypoleuca can reproduce by fragmentation, all thalli that were encountered are included in this estimate. Thirty-four extant subpopulations occur in Ontario, one in Quebec, and one in New Brunswick (Table 4). Ontario contains most individuals, with 465 thalli (98%) on 138 trees (96%), followed by Quebec with 10 thalli (2%) on 5 trees (4%), and New Brunswick with one thallus on one tree (<1%).

The distribution of mature individuals among the three occupied Ecological Areas (EA) is as follows: 331 (70%) individuals on 93 (65%) trees representing 20 subpopulations in the Great Lakes Plain EA, 144 (30%) individuals on 50 (35%) trees representing 15 subpopulations in the Boreal EA, and 1 individual representing a single subpopulation (1%) in the Atlantic EA. The distribution of individuals among substrate types is presented in Figure 7 (see Habitat requirements).

Figure 7. Number and type of alive and dead trees occupied by Heterodermia hypoleuca at extant subpopulations in Canada.

An estimated subpopulation size was completed for Ontario to account for additional individuals possibly present on inaccessible private land in eight eastern Ontario counties including Ottawa, Hastings, Lanark, Leeds and Grenville, Lennox and Addington, Peterborough, Prince Edward, and Renfrew. It was projected that an additional 580 to 900 mature individuals on 190 to 270 ash trees (refer to Appendix 2 for an explanation of these values) could occur within approximately 250 km² of unsurveyed suitable habitat identified by examining digital geospatial datasets including forest cover, landownership, and surficial geology. However, mortality rates for these individuals would likely approach 100% within three generations (30 to 90 years) as they are assumed to occur on ash, which is vulnerable to the threat of EAB. When combined with the 2012 to 2024 survey data, the total Canadian population is estimated to be between 1,056 and 1,376 individuals on 334 to 414 host trees.

Fluctuations and trends

There has been no long-term monitoring of H. hypoleuca in Canada. As a result, there are no data to estimate trends over time. However, since much of the original productive, mature forest cover in the Great Lakes Plains region home to almost two thirds of the Canadian population has been lost, it is likely that H. hypoleuca has experienced a decline here. Review of both historical literature (for example, Billings 1860) and supporting vouchered specimens made mostly prior to the 20th century, suggests H. hypoleuca was previously more widespread since it was found in areas where suitable habitat no longer exists. Early records from southern Ontario where it was recorded at Wooler, Brighton, Ottawa, near Hull, and Prescott lack suitable habitat at present, and are considered extirpated (Table 2). Early literature reports from Algonquin Park and Lake Nipigon (Macoun 1902) cannot be verified.

In Ontario, recent documented losses over the last five years of at least 20 thalli at three subpopulations have been observed (12 at Frontenac Provincial Park, 7 at Belmont Lake, and 1 at Darling Long Lake) and another 4 are suspected (Deseronto Rd.). Prior to 2019, there were 15 individuals reported from Frontenac Provincial Park on four trees (Lewis 2019). Two of the four occupied trees were dead and on the ground hosting 12 of the 15 individuals. A targeted search during this status report by SB failed to relocate any individuals on downed ash trees in the same areas. Thus, the 12 individuals on those two trees have presumably been lost. Six thalli on a recently downed ash at Belmont Lake found by SB in 2022 was revisited in 2024, and all thalli were gone and the bark had fallen off the trunk, and another thallus was no longer present on a nearby Bur Oak. A single thallus was found by RL at Darling Long Lake in 2001 on a downed Sugar Maple. It is presumed to have been lost. Four individuals found by CL at the Deseronto Rd. subpopulation occur on private land in a deciduous swamp adjacent to a road. SB viewed this area in 2020 from the ditch and noted all the Green Ash trees in the deciduous swamp were near dead or dead standing due to EAB infestation. The number of individuals at this subpopulation has presumably declined and may be extirpated now because the host trees appeared to no longer provide suitable habitat.

Between 2019 and 2024, 102 thalli were recorded on 38 dead standing or fallen dead host trees (Figure 7). Bark on these tree hosts was in various stages of deterioration but will soon fall off or decompose, and therefore these individuals will be lost. Over the next five years, there will be an estimated 21% decline in number of mature individuals (unit of count is the total number of observed thalli). This increases to a 35% decline when considering the number of occupied trees that will be lost.

The status of the five historical subpopulations in Quebec is unknown, but their scattered distribution suggests a previously more widespread distribution there. At least two historical collections were made from elm, and it is likely these are no longer extant, as mature elms have been decimated range-wide by Dutch Elm Disease (see Threats and limiting factors).

A total of 253 individuals were recorded on living ash trees between 2019 and 2024, and all of these will presumably die as ash trees succumb to Emerald Ash Borer, which is a threat throughout the entire Canadian range of H. hypoleuca (CFIA 2021). Currently, EAB has been found already at 15 extant subpopulations and is projected to impact an additional 16 over the next three generations (30 to 90 years). When accounting for losses of all individuals on ash trees and on dead trees, the Canadian population is projected to decline by 78% over the next three generations. The decline is 74% if relying on the number of occupied host trees that will be lost (due to EAB or other causes).

Rescue effect

Recruitment via long-distance transport of ascospores from sites outside Canada is conceivable, though given the distances involved, it is impossible to determine how likely this is. The nearest extant site to the Canadian border is in north-central Minnesota (Thayer and Henderson pers. comm. 2019). This site is several 100 kilometres south of the Rainy River District of Ontario, where no records of H. hypoleuca exist. While potentially suitable habitat exists based on recent surveys, targeted searches have not been successful in this region (refer to Table 1 and Figure 4 for a summary of search effort).

The nearest extant site to the Canadian population lies over 600 km to the south in central Ohio (Curtis pers. comm. 2022). Other records from adjacent U.S. jurisdictions found in CLH (2023) are historical (>20 years) and their status is unknown. Given the distances involved and the lack of recent collections in most adjacent states, rescue from these populations seems unlikely.

Threats and limiting factors

Historical, long-term, and continuing habitat trends

The extent and quality of productive mature forest stands in Eastern North America, and particularly their unique interior microclimates constituting the range of H. hypoleuca in Canada, has undoubtedly diminished significantly since European settlement, which has resulted in the loss of a large portion of suitable habitat (see Habitat trends). Early accounts of lichens in southern Ontario including those of Billings (1860) and Macoun (1902) indicate numerous pollution-sensitive and disturbance-sensitive taxa such as Anzia colpodes, Lobarina scrobiculata, Nephroma resupinatum, and Usnea angulata were present in southern Ontario in the 19^th or early 20^th centuries. However, later-twentieth-century studies (for example, Brodo 1981; Wong and Brodo 1992) and extensive lichen surveys carried out since then by numerous lichenologists in the same region, have failed to document any individuals of these species, a trend that has been observed elsewhere in the northeast (Allen et al. 2019).

Current and projected future threats

The overall threat impact based on the Threats Calculator assessment for H. hypoleuca is Very high – High (Appendix 3). The overall threat impact is calculated by considering the separate impacts of all threat categories. The various threats, in order of importance, include natural system modifications, climate change and severe weather, biological resource use, and transportation and service corridors. Each threat is discussed below.

Natural system modifications (IUCN threat 7.3 other ecosystem modifications); overall threat impact: very high – high

Emerald Ash Borer (EAB) is a wood-boring beetle native to East Asia that is dramatically altering temperate forests in North America where ashes are an important forest canopy component. For most ash species, infestation by EAB causes over 90% mortality of trees with a diameter greater than 2.5 cm (at breast height) within a few years (Klooster et al. 2014). EAB was first detected in southwestern Ontario in 1992 and has since spread to Canadian sites up to 1,100 km northwest and 1,300 km northeast (COSEWIC 2018). EAB larvae feed on the inner bark and sapwood, eventually girdling and killing trees (Herms and McCullough 2014). Mortality of mature ash trees (all species) reached 99% within six years in parts of Michigan and Ohio (Klooster et al. 2014), and similar rates of ash mortality has been noted in affected areas of southern Ontario (COSEWIC 2018). Widespread ash tree mortality caused by EAB is the most serious threat currently facing H. hypoleuca in Canada (Figure 8). Heterodermia hypoleuca is completely dependent on its host trees for its continued survival. As ash trees succumb, the availability of mature, ash-dominated swamp forest habitat in southern Ontario will decline as is expected in other Northeastern regions (Youngquist et al. 2017; Palik et al. 2021).

Figure 8. Photographs depicting mature Green Ash mortality in Heterodermia hypoleuca habitat caused by Emerald Ash Borer (EAB) in Ontario. A) Large diameter, dead-standing Green Ash tree with most of its bark descaled after EAB infestation. B) Closeup of Heterodermia hypoleuca on tree infected with EAB with portion of thallus lost from descaling bark. C) Looking upwards at a Green Ash infected with EAB with approximately 50% of bark descaled (photos S. Brinker).

In Canada, ash trees are the most important host substrate (Table 3 and Figure 7). EAB already occurs at a minimum of 15 of the 31 subpopulations with ash as a host substrate. While EAB was not detected at all sites, the entire Canadian range of H. hypoleuca is within EAB regulated areas where it is well established and spreading (CFIA 2021). This means that over the next three generations (30 to 90 years), it is projected that all occupied ash trees will likely succumb to EAB. This will result in a loss of 74% of the Canadian population (351 thalli or 107 host trees).

^a Substrate codes: AS = Acer saccharum; CC = Carya cordiformis; FN = Fraxinus nigra; FP = Fraxinus pennsylvanica; QM = Quercus macrocarpa; QR = Quercus rubra; TA = Tilia americana; TO = Thuja occidentalis. – Dashes indicated missing information which is often the case for older collections and observations.

^b EAB = Emerald Ash Borer (Agrilus planipennis) observed in occupied habitat.

? Indicates an unknown value or a degree of uncertainty about status and should be a priority for future assessments.

~ Indicates an estimate derived from the interpretation of available information (rather than an explicit count).

Two historical H. hypoleuca records were collected on elm bark in Quebec. Dutch Elm Disease (DED) impacting native elms (Ulmus spp.) in North America was first detected in the U.S. in the 1930s and rapidly caused widespread and devastating losses to mature elm trees. Its detection in Canada soon followed, first in 1944 in Quebec, and then in Ontario by 1948 (Reed 1950). Its impact was swift as its rate of spread was over 1,900 km a year (Pomerleau 1961). The drastic loss of mature elm trees across the range of H. hypoleuca in Canada has likely resulted in the loss of subpopulations occurring on elm trees, as well as a suitable host substrate. Dutch Elm Disease’s continued impact on elms is apparent since the last recorded thallus from elm bark was from sometime between the late 1960s and early 1970s. At present, while emerging elm seedlings or root suckers from infected trees can reach sexual maturity, trees no longer attain suitably large trunk diameters and bark characteristics prior to the onset of DED attacks (Brasier 1986, 1996), which likely accounts for the absence of recent observations of H. hypoleuca on elm bark.

Climate change and severe weather (IUCN threats 11.4 storms and flooding); overall threat impact: high – low

The full impacts to lichens resulting from anthropogenic climate change are still unclear, partially due to a lack of sufficient study. While a growing body of research suggests that the consequences of climate change could be severe for lichens (Allen and Lendemer 2016; Ellis 2013, 2015), more studies are needed to properly characterize the threat level. In a study of threats to at-risk species in Canada, lichens as a group were found to be the most highly affected taxon of the 12 taxonomic groups assessed (Woo-Durand et al. 2020).

In Canada, nine of the 10 warmest years have occurred during the last 25 years, with 2010 being the warmest on record (3.0°C above the 1961 to 1990 reference value) (ECCC 2023). The effects of widespread warming are evident in many parts of Canada and are projected to intensify in the future. In southern Ontario and Quebec, warmer temperatures are predicted to give drier conditions, especially during the summer months, leading to lower water levels in the Great Lakes region (Feltmate and Thistlethwaite 2013). Projected changes to mean annual temperature would lead to net warming and drying, likely reducing available moisture and humidity, important habitat characteristics for H. hypoleuca (see Habitat). Alteration of hydrological regimes (that is, changes in the amount of precipitation, increased frequency of drought) may also impact the distribution and abundance of suitable host trees in most H. hypoleuca habitat. In a climate change vulnerability assessment of species in the Ontario Great Lakes Basin, Black Ash was found to be moderately vulnerable to climate change in part due to its physiological hydrological niche (its degree of dependence on specific swamp/vernal pool wetland habitat) that is modelled to experience net drying with increasing temperatures (Brinker et al. 2018).

Radical shifts in regional climate envelopes (areas with similar climate regimes) are expected and have been predicted for Ontario based on climate modelling completed by McKenney et al. (2010). Under these scenarios, species with narrow habitat requirements and limited dispersal success, such as H. hypoleuca, may be more vulnerable than habitat generalists, or those with more effective dispersal abilities.

An increase in the frequency and severity in weather events, including blow-down of host trees or physical damage from ice storm activity, is expected with a warming climate (ECCC 2017). A derecho (a widespread, long-lived windstorm associated with a band of rapidly moving showers or thunderstorms) event that occurred in May of 2022 and a tornado later in July along nearly the same path across eastern Ontario (Figure 9) caused widespread and severe damage to the fragmented forest cover in the region, affecting both suitable unsurveyed habitat (Figure 10) and occupied habitat. Recently downed mature trees with H. hypoleuca, which were observed at six subpopulations (totalling at least 22 thalli), were likely—based on the condition of individuals and trees with leaves still attached—toppled during these storm events.

Figure 9. Path of the May 2022 Ontario-Quebec derecho causing extensive damage to forest cover leading to loss of mature trees hosting Heterodermia hypoleuca (modified from Northern Tornadoes Project 2023). The yellow area indicates the general continuous path of the derecho roughly 1,000 km in length, and 100 km in width. The blue areas indicate intensified areas of severe damage. White circles represent extant H. hypoleuca subpopulations.

Figure 10. Severe damage to swamp forest caused by 2022 derecho event (corresponding to area of blue in Figure 9) in eastern Ontario (photo S. Brinker).

Biological resource use (IUCN threats 5.3 logging and wood harvesting, and 5.2 gathering terrestrial plants); overall threat impact: medium – low

Lichens are directly impacted by timber harvesting because logging means that individuals are removed from the forest together with their substratum. While Eastern White Cedar, Green Ash, Red Oak, and Sugar Maple are merchantable timber, other host trees, namely Black Ash and Bur Oak, are not often target species in forestry operations. Species of ash are generally regarded as high-quality firewood (Alden 1994) and may be targeted for harvest in private woodlots throughout the species’ range. At least seven extant subpopulations occur on private land not managed for conservation, though this threat extends to eight on conservation authority-owned land, two municipally owned subpopulations and eight subpopulations on unprotected Crown land, where commercial timber harvesting, or salvage operations may occur. Individuals in these subpopulations make up about 39% of the total Canadian population and could be impacted during logging or salvage activities.

Ash mortality due to Emerald Ash Borer has increased the selective logging of ash trees. In several Northeast U.S. jurisdictions, foresters and loggers have responded to EAB infestations by increasing harvests of ash trees including small-diameter and low-grade trees to promote regeneration of other more merchantable timber (Markowski-Lindsay et al. 2023). While no data are available from Canada, SB has observed increases in selective ash harvesting in forests of southern Ontario where EAB infestations exist.

The removal of hazard trees from managed areas including provincial parks, particularly trees adjacent to roads, day-use areas, trails or campsites, may result in the removal of occupied trees. At Silver Lake Provincial Park, two downed basswood trees were observed around campsites with felled portions of the trunks left on the ground, hosting several H. hypoleuca thalli. Similarly, municipalities may prioritize removal of ash trees from public lands before they became hazardous.

Increased visitation and incidences of collecting thalli could result in mortality because rare and at-risk species tend to spike public interest. Increased collecting pressure or inadvertent damage to individuals from general lichen collecting could come with increased awareness of this rare species, a phenomenon observed elsewhere for listed plant species (for example, Sutter 1987). However, this threat is difficult to document and likely negligible.

Transportation and service corridors (IUCN threat 4.1 roads and railroads); overall threat impact: low

Road construction associated with forestry activities can damage H. hypoleuca habitat if routed through or too close to areas of occupancy. Routing logging roads too close to swamp forest habitat or vernal ponds can alter their hydrological processes, reduce local humidity levels, and decrease host tree availability, if removal of trees along the edge of habitat occurs. In Ontario, if sites are identified on Crown land, protection can be provided via a 30 m buffer to woodland pools through Ontario’s Forest Management Guide for Conserving Biodiversity at the Stand and Site Scales (OMNR 2010). This relies on the correct delineation of pools, which can be misinterpreted if conducted outside the appropriate season, and assumes that staff are trained to identify H. hypoleuca; it would not apply to private land.

Several threats were considered unknown including: the effect of airborne pollutants, climate change resulting in habitat shifts, and alteration and droughts. Details are provided in the Threats Calculator.

Limiting factors

Mode of reproduction and dispersal, as well as the availability of suitable host substrates for lichen colonization, are key limiting factors that have been found to impact lichen rarity. In the predominantly managed landscape where H. hypoleuca occurs, long distances between habitat patches and a limited dispersal range may limit colonization of potentially suitable habitat. Apothecia were absent from thalli at 12 of the 36 extant subpopulations (Appendix 1). Lichens that reproduce sexually, dispersing only the mycobiont, and that are restricted to trees as a substrate are overrepresented among rare species in temperate eastern North American forests (Manzitto-Tripp et al. 2022). Heterodermia hypoleuca joins a growing list of declining macrolichens of temperate northeastern North American mature broad-leaved forests, reproducing primarily via ascospores produced in apothecia that are restricted to growing on tree trunks. Other examples include Anzia colpodes and Myelochroa galbina (COSEWIC 2015; Tripp and Lendemer 2020).

Number of locations

Six locations based on the most plausible threat are identified for H. hypoleuca in Canada. All 36 extant subpopulations fall within the Canadian Food Inspection Agency’s Regulated Zone for Emerald Ash Borer (CFIA 2021), though not all individuals occur on ash. Thalli at 31 subpopulations occur on ash trees and are considered a single location. At these sites, individuals are either already being impacted by EAB or are at a very high risk of being impacted within the next decade (one generation, 10 to 30 years), based on natural expansion rates of 20 km per year (Prasad et al. 2010) or potentially much greater rates owing to human-assisted expansions (such as deliberately moving ash wood) (DeSantis et al. 2013). The impact of climate change on H. hypoleuca is uncertain, but could become a more serious threat in the next three generations (30 to 90 years) and would likely affect each subpopulation separately. The remaining five subpopulations are treated as separate locations.

Protection, status, and ranks

Legal protection and status

There is currently no legal status or protection for H. hypoleuca. It is not covered under the Convention on International Trade in Endangered Species (CITES) or the United States’ Endangered Species Act.

Non-legal status and ranks

Global status

Heterodermia hypoleuca has been assigned a global rank of G5 (Secure), although this rank was last reviewed in 1992 (NatureServe 2023) and should be re-evaluated. It has not been assessed by the International Union for the Conservation of Nature (IUCN).

Status in Canada

In Canada, H. hypoleuca is ranked N3 (Vulnerable), but will likely change to N2 due to a revision in Quebec (Tremblay pers. comm. April 2025). In Ontario, it has a subnational rank of S2 (Imperiled). In Quebec, it is currently ranked S3 (Vulnerable) (NatureServe 2023), although this status may overestimate its security since there is only one extant subpopulation. It is being revised to S1S2 (Tremblay pers. comm. April 2025). Its status has not yet been assessed in New Brunswick.

Status in the U.S.

In the United States, H. hypoleuca has a national rank of NNR (unranked), and it has a rank of S5 (secure) in Kentucky and SNR in Georgia, North Carolina, Pennsylvania, and Wisconsin (NatureServe 2023). Other states where it occurs do not currently assign a rank to the species.

Habitat protection and ownership

In Ontario, 11 extant subpopulations occur in protected areas (Appendix 1). Of these, 8 fall within regulated provincial parks and conservation reserves and 3 are within lands owned and managed for conservation purposes by the Nature Conservancy of Canada. Two occur on private lands managed for conservation. Another 18 occur on lands owned and managed by conservation authorities, municipalities or on Crown land, where logging operations may still occur, and it is uncertain whether some of these are managed for biodiversity conservation. At least 6 subpopulations occur entirely on privately owned land not managed for conservation purposes.

In Quebec, the only extant subpopulation occurs on private land managed for conservation purposes (a migratory bird sanctuary). The remaining historical records do not provide sufficient spatial information to determine land ownership. However, a specimen labelled “Gatineau Park” might correspond with federal lands now managed by the National Capital Commission, and a specimen collected from Île Bonaventure may correspond with lands currently owned by Sépac (Société des établissements de plein air du Québec), which manages parks and wildlife reserves.

Land tenure of the newly discovered subpopulation in New Brunswick is under private ownership.

Acknowledgements

Assistance with documenting the presence and distribution of H. hypoleuca in Canada has been provided by many colleagues. The following are graciously thanked for their generous assistance with fieldwork: Graham Cameron, Cassandra Robillard, Christine Terwissen, and Alison Smith with the Ontario Ministry of Natural Resources and Forestry; Colin Chapman-Lam, consulting lichenologist and botanist based in Ottawa, Canada; Josh Van Wieren and Mary Beth Lynch with Parks Canada; and Tim Trustham and Robert Ormston with Quinte Conservation. Jon Ruddy is thanked for sharing his recent discoveries of H. hypoleuca in eastern Ontario.

The Ontario Ministry of Natural Resources and Forestry provided in-kind support for the Ontario fieldwork component. Arold Lavoie provided insight on the status of the species in Quebec. Stephen Clayden provided valuable information on his recent discovery of the species in New Brunswick. Tomas Curtis provided helpful insight on the status and habitat in Ohio. John Thayer, Otto Gockman and Bobby Henderson provided helpful insight on the status and habitat in Minnesota. Chris Lewis, Chris Deduke, Troy McMullin, Gregory Rand, Gina Schalk, Marie Archambault, Jenna Siu, Mary Sabine, Leah de Forest, and Richard Caners kindly provided useful comments on a previous draft. Thanks to Dwayne Lepitzki for facilitating the threats call and to Jennifer Doubt, Chris Deduke, Toby Spribille, Marc Favreau, Cassandra Robillard, Tegan Padget, and Julie McKnight for participating in it.

Authorities contacted

• Frances Anderson, Lichenologist, Nova Scotia Museum, Nova Scotia
• Dr. Stephen Clayden, Curator (retired), New Brunswick Museum (NMB), New Brunswick
• Dr. Chris Deduke, Canadian Museum of Nature (CANL), Gatineau, Quebec
• Dr. Ted Esslinger, Professor Emeritus, North Dakota State University, North Dakota
• Bobby Henderson, Botanist, U.S. Forest Service, Minnesota
• Dr. Robert Klips, Associate Professor Emeritus, Ohio State University, Ohio
• Jacques Labrecque, Botanist (retired), Ministère de l'Environnement, de la Lutte contre les changements climatiques, Quebec
• Arold Lavoie, Independent Lichenologist, Quebec
• Rob Lee, Independent Lichenologist, Ontario
• Chris Lewis, Species at Risk Biologist, Government of British Columbia
• Dr. Troy McMullin, Lichenologist, Canadian Museum of Nature
• Dr. James Lendemer, Lichenologist and Curator of Botany, New York State Museum
• Dr. Michele Piercey-Normore, Special Advisor to the President, Algoma University, Thunder Bay
• Mr. Jon Ruddy, Research Associate, Canadian Museum of Nature

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Biographical summary of report writer

Samuel Brinker (SB) is the provincial botanist and lichenologist with the Natural Heritage Information Centre (NHIC) in the Science and Research Branch of the Ontario Ministry of Natural Resources. In this role, he conducts lichen surveys and biodiversity assessments across the province to monitor their distribution and status. He is a NatureServe member botanist and is responsible for maintaining provincial conservation status ranks for vascular plants and lichens, as well as plant and lichen occurrence data for the province. Since beginning with NHIC in 2009, he has discovered dozens of lichens new to North America, Canada, and Ontario as well as new species to science. Sam is a member of the COSEWIC Vascular Plant Species Specialist Committee and has written or co-written numerous COSEWIC and provincial status reports on lichens and vascular plants.

Collections examined

Specimens housed at the following herbaria/websites were consulted with respect to records of Heterodermia hypoleuca in Canada:

• Canadian Museum of Nature, Lichen Herbarium, Gatineau (CANL)
• Louis-Marie Herbarium, Université Laval, Quebec City (QFA)
• Consortium of Lichen Herbaria (CLH)
• New York Botanical Garden, Bronx, New York (NYBG)

Appendix 1. Collection details and land tenure for all Canadian subpopulations

^a Source codes for collectors: BB = Braddish Billings; SB = Samuel Brinker; SC = Stephen Clayden; AH = Ann Hanes; RH = Richard Harris; FL = Fabius LeBlanc; RL = Rob Lee; CL = Chris Lewis; JM = John Macoun; JR = John Ruddy; ET = Eric Thorn.

^b Herbarium codes: CANL = Canadian Museum of Nature (Lichens); FH = Harvard University; NEB = University of Nebraska State Museum; NY = New York Botanical Gardens; QFA = Louis-Marie Herbarium; REL = private herbarium of Rob Lee.

Appendix 2. Method for estimating number of individuals and occupied host trees on unsurveyed private land in Ontario

This analysis includes 2019 to 2024 data collected by Sam Brinker (SB) from 45 distinct sites (at least 1 km apart) with suitable habitat on public land between Peterborough and the Ottawa River, where ash trees are the primary host substrate, in locations that had no previous records. This search effort yielded 16 new subpopulations, or a 35% search success rate.

Data used in this assessment incorporates low and high counts to provide a range estimate to reflect some uncertainty. Scenario 1 incorporates 15 subpopulations consisting of 101 individuals on 34 ash trees (the low estimate excluding unusually large Constant Creek subpopulation that may skew the typical habitat based on its extent). Scenario 2 incorporates 16 sites consisting of 154 on 50 trees (the high estimate including Constant Creek subpopulation).

Calculations to determine amount of suitable private land habitat

Approximately 36,871 km² total area in eight counties in eastern Ontario where Heterodermia hypoleuca ranges: City of Ottawa†, Hastings, Lanark, Leeds and Grenville, Lennox and Addington†, Peterborough, Prince Edward, and Renfrew († denotes counties with no records but likely present).

Approximately 27,431 km² of this is private land, or about 74% (in private ownership).

Of that private land, approximately 21,890 km² is underlain by suitable calcareous substrata (the remainder is acidic bedrock and not considered suitable).

Of this remaining area, approximately 250 km² contains stands with Black Ash based on Forest Resource Inventory values (Black Ash used as a proxy since Green Ash is not differentiated).

For estimation purposes, each subpopulation is assumed to exist within a unique 1 km² area.

With 250 km² of unsearched suitable habitat on private land, the potential number of individuals and host ash trees in these areas can be estimated as follows:

• Low = 6.7 individuals per km² × 250 km² = 1,675 individuals
• High = 10.2 individuals per km² × 250 km² = 2,550 individuals

• Low = 2.2 trees per km² × 250 km² = 550 host trees
• High = 3.1 trees per km² × 250 km² = 775 host trees

Given the 35% search success rate obtained on public land in similar habitat:

• Low = 35% of 1,675 individuals = 586 individuals (approximately 580)
• High = 35% of 2,550 individuals = 892 individuals (approximately 900)

• Low = 35% of 550 host trees = 192 (approximately 190)
• High = 35% of 775 host trees = 271 (approximately 270)

Assumptions made

• Heterodermia hypoleuca occurs at roughly 5 to 8 thalli per square kilometre where preferred habitat consists of forest units with a Black/Green Ash component
• Heterodermia hypoleuca occurs on roughly 2 to 3 host ash trees per square kilometre where preferred habitat consists of forest units with a Black/Green Ash component
• Forest Resource Inventory data used was accurate (which we understand is not always true)
• Forest Resource Inventory data indicating the presence of Black Ash does not distinguish Green Ash from Black Ash, but its presence indicates saturated. mineral soil (for at least a portion of the year) and excludes upland areas of White Ash
• Land tenure data used was accurate (which may not always be true)
• Surficial geology mapping data was accurate (which we understand is not always true)

Limitations

• Forest Resource Inventory stand description (tree species composition) data covers only 61% (22,600 km²) of the total area for calculations

Appendix 3. Threats calculator assessment for the Cupped Fringe Lichen (Heterodermia hypoleuca)

Species scientific name: Cupped Fringe Lichen (Heterodermia hypoleuca)

Date: 3/4/2024

Assessor(s):

Dwayne Leptizki (Facilitator)
SR writer: Sam Brinker
M&L SSC: Jennifer Doubt, Chris Deduke, Toby Spribille, Marc Favreau, Cassandra Robillard, Tegan Padgett
External participant: Julie McKnight (ECCC)

References: Draft calculator provided by writer S. Brinker. Draft COSEWIC report, teleconference from March 7, 2024.

Assigned overall threat impact:

AB = Very high – High

Overall threat comments:

Estimated generation time: 10 to 30 yrs (for an ascospore to land and grow into a lichen producing fruit bodies that release spores). Therefore, the severity and temporal range is 30 to 90 years into the future. Southern ON, QC, and recent (from 2022) NB (fig 2, pdf), but assessed as single DU because of its continuous distribution and no obvious disjunctions. It is an indicator of high-quality, rich, humid, mature hardwood forest stands, sites close to water, most likely due to humidity; primarily (74%) ash trees; approximately 98% of 476 thalli (in 34 subpopulations) in ON, 2% in QC (1 subpopulation), <1% NB (1 subpopulation). Of the total, 24% (102 individuals) on dead/downed trees and are not expected to survive. Known subpopulations have been lost. There is a 78% loss of entire Canadian population projected due to EAB and recent storm events. There are 13 subpopulations in provincial parks or privately managed lands for conservation; 18 subpopulations occur on “unprotected” lands. Scores for scope below are based on individuals, not subpopulations.

Classification of Threats adopted from IUCN-CMP, Salafsky et al. (2008).