Hibberson’s Trillium (Trillium hibbersonii): COSEWIC assessment and status report 2023

Official title: COSEWIC assessment and status report on the Hibberson’s Trillium (Trillium hibbersonii) in Canada

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

Threatened

2023

COSEWIC assessment summary

Assessment summary – May 2023

Common name: Hibberson’s Trillium

Scientific name:Trillium hibbersonii

Status: Threatened

Reason for designation: This Canadian endemic perennial plant is globally restricted to a small area on the west coast of Vancouver Island in British Columbia. It is distributed in seven subpopulations, most with less than a few hundred individuals, on rocky outcrops and cliffs with seasonal seepages near ocean, river, and lake shorelines. It is threatened by the continuing decline of its habitat from landslides, severity of storms and flooding due to climate change and, indirectly, from forest-harvesting activities increasing erosion and altering seepage patterns. The limited population size and number of subpopulations makes the species vulnerable to these stochastic events.

Occurrence: British Columbia

Status history: Designated Threatened in December 2023.

COSEWIC executive summary

Hibberson’s Trillium

Trillium hibbersonii

Wildlife species description and significance

Hibberson’s Trillium is a small perennial herb with three broadly ovate leaves. The flowers grow on a short pedicel and have three pink petals that are offset with three green, fully divided sepals.

Hibberson’s Trillium is endemic to the west coast of Canada. Its showy flowers and diminutive stature have made it a sought-after horticultural species.

Aboriginal (indigenous) knowledge

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

Distribution

Hibberson’s Trillium occurs only in British Columbia and is known from seven subpopulations on the west coast of Vancouver Island, in the vicinity of Kyuquot Sound, Hesquiat Lake and Sydney Inlet.

Habitat

Hibberson’s Trillium is found in the Coastal Western Hemlock biogeoclimatic zone. Most subpopulations occur at low elevations in thin, poorly developed soils next to the ocean or a lake. Six of the subpopulations are found in thick layers of moss and lichen on open rocky ledges, outcrops, and cliffs with seasonal seepage. The seventh subpopulation occurs in small mossy clefts in rock in a riparian area that is inundated during peak flows.

Biology

Hibberson’s Trillium has been grown from offsets, and has flowered in three or four years from seed sown in pots; reproduction in the wild has not been studied. In a garden setting, Hibberson’s Trillium can persist for at least 35 years. The stems emerge annually from a rhizome in the spring and bloom in early April. Pollinators of other Trillium species include flies, bees and beetles. Dispersal agents of other Trillium species include ants, wasps, ground beetles and banana slugs, which are attracted to a lipid-rich attachment on the seeds and help to disperse the seeds. Plants are eaten by bears and deer, which may also act as seed dispersers. Seeds and seedlings may also be dispersed by water.

Population sizes and trends

A summation of the most recent survey data (2014 to 2023) for all seven subpopulations provides an estimated total of 1,220 to 1,370 mature flowering Hibberson’s Trillium individuals. The number of flowering plants per subpopulation ranges from approximately 20 plants to 400 to 450 plants. No monitoring or population modelling data are available for determining fluctuations and trends.

Hibberson’s Trillium has persisted in four subpopulations, which have had repeat visits since they were first documented in 1938, 1958, 1981 and 2001. The three other subpopulations were discovered in 2019, and two of these were re-surveyed in 2023. Ongoing habitat loss is occurring in unprotected areas, which may contain undocumented subpopulations.

Threats and limiting factors

The overall threat impact for Hibberson’s Trillium is considered Medium - Low. Timber harvesting in both Hibberson’s Trillium habitat and upslope areas may alter seepage patterns, cause erosion and result in landslides. Storms and flooding associated with extreme precipitation events may trigger landslides. Climatic shifts may cause the premature drying of seepage areas, extreme weather events and sea-level rise, all of which could impact the species.

Protection, status, and recovery activities

Hibberson’s Trillium is ranked S3 (Vulnerable) provincially, N3 (Vulnerable) nationally, and G3 (Vulnerable) globally. The species does not currently benefit from legal protection and is not listed under the Species at Risk Act; nor is it listed under the Convention on International Trade in Endangered Species (CITES).

The International Union for Conservation of Nature (IUCN) currently considers Hibberson’s Trillium to be a sub-taxon of Western Trillium (listed as Least Concern on the Red List), but has recognized that Hibberson’s Trillium requires designation as a full species. As a separate species, Hibberson’s Trillium will likely be categorized as Vulnerable under category D1 (very small or restricted population), but data were lacking at the time of assessment.

Four of the known Hibberson’s Trillium subpopulations are in B.C. provincial parks, and the remaining three are on provincial Crown land.

Technical summary

Trillium hibbersonii

Hibberson’s Trillium

Trille de Hibberson

Range of occurrence in Canada: British Columbia

Demographic information

Generation time (usually average age of parents in the population)

10 to 20 years

Based on inferred average age of parents

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

Yes

Inferred continuing decline based on ongoing threats

[Observed, estimated, or projected] percent of continuing decline in total number of mature individuals within 3 years [or 1 generation; whichever is longer up to a maximum of 100 years]

Unknown

Unknown

Observed, estimated, or projected] 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]

Unknown

Unknown

[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]

Unknown

No long-term surveys have been done to determine population trends, and there have been no consistent re-counts of known subpopulations.

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

Unknown

Unknown

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

Unknown

Unknown

Are the causes of the decline clearly reversible?

Unknown

Unknown

Are the causes of the decline clearly understood?

Unknown

Unknown

Are the causes of the decline clearly ceased?

Unknown

Unknown

Are there extreme fluctuations in number of mature individuals

Unknown

Inferred generation time and observed persistence of plants in four subpopulations that have been revisited suggest relative stability, but it is unknown if fluctuations occur.

Extent and occupancy information

Estimated extent of occurrence (EOO)

448 km²

Calculated based on minimum convex polygon around all known occurrences

Index of area of occupancy (IAO), reported as 2x2 km grid value

40 km²

Based on data collected in 2014 to 2023

Is the population “severely fragmented”, that is, is >50% of individuals or >50% of the total area “occupied” (as a proxy for number of individuals) in habitat patches that are both (a) smaller than required to support a viable subpopulation, and (b) separated from other habitat patches by a distance larger than the species can be expected to disperse?

1. No
2. Yes

The persistence of plants in four subpopulations since they were first recorded suggests these habitat patches are of sufficient size to support viable subpopulations.

Subpopulations are widely separated from other habitat patches by a distance larger than the species can be expected to disperse.

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

7

Based on threats, each subpopulation is a single location.

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

No

Inferred based on persistence of all known subpopulations

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

No

Inferred based on persistence of all known subpopulations

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

No

Inferred based on persistence of all known subpopulations since first recorded

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

No

Inferred based on persistence of all known locations/subpopulations since first recorded

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

Yes

All known subpopulations have persisted, but there is an inferred decline due to ongoing logging in areas outside of protected areas, impacting the quality and area of habitat.

Are there extreme fluctuations in number of subpopulations?

No

Inferred based on persistence of all known subpopulations

Are there extreme fluctuations in number of “locations”?

No

Inferred based on persistence of all known locations/subpopulations

Are there extreme fluctuations in extent of occurrence?

No

Inferred based on persistence of all known subpopulations

Are there extreme fluctuations in index of area of occupancy?

No

Inferred based on persistence of all known subpopulations

Number of mature individuals (by subpopulation)

Numbers correspond to latest count of flowering plants listed in Table 1

Quantitative analysis

Is the probability of extinction in the wild at least 20% within 20 years [or 5 generations], or 10% within 100 years]

Unknown

Analysis not conducted

Threats

Was a threats calculator completed for this species?

Yes (see Appendix 1)

Overall assigned threat impact: Medium - Low (2023)

Key threats were identified as:

1. Biological Resource Use: Logging and Wood Harvesting (IUCN 5.3) – Medium - Low
2. Geological Events: Avalanches/Landslides (IUCN 10.3) – Medium - Low
3. Climate Change and Severe Weather: Storms and Flooding (IUCN 11.4) – Low

What limiting factors are relevant?

• Restricted habitat
• Low fecundity
• Limited dispersal

Rescue effect (from outside Canada)

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

N/A

Does not occur outside of Canada

Is immigration known or possible?

No

Does not occur outside of Canada

Would immigrants be adapted to survive in Canada?

N/A

Does not occur outside of Canada

Is there sufficient habitat for immigrants in Canada?

N/A

Does not occur outside of Canada

Are conditions deteriorating in Canada?

Yes

Habitat is limited, and logging occurs in areas that may have undocumented subpopulations outside of protected areas.

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

N/A

No outside source population

Is the Canadian population considered to be a sink?

N/A

Does not occur outside of Canada

Is rescue from outside Canada likely, such that it could lead to a change in status?

N/A

Does not occur outside of Canada

Wildlife species with sensitive occurrence data (general caution for consideration)

Could release of certain occurrence data result in increased harm to the Wildlife Species or its habitat?

No

Sites are remote and challenging to access; maps are not at a scale that identifies specific sites.

Status history

COSEWIC: Designated Threatened in December 2023.

Status and reasons for designation

Status: Threatened

Alpha-numeric codes: B1ab(iii)+2ab(iii); C2a(i)

Reason for change in status: Not applicable

Reasons for designation: This Canadian endemic perennial plant is globally restricted to a small area on the west coast of Vancouver Island in British Columbia. It is distributed in seven subpopulations, most with less than a few hundred individuals, on rocky outcrops and cliffs with seasonal seepages near ocean, river, and lake shorelines. It is threatened by the continuing decline of its habitat from landslides, severity of storms and flooding due to climate change and, indirectly, from forest-harvesting activities increasing erosion and altering seepage patterns. The limited population size and number of subpopulations makes the species vulnerable to these stochastic events.

Applicability of criteria

A: Decline in total number of mature individuals:

Not applicable.

Insufficient data to reliably infer, project or suspect population trends

B: Small range and decline or fluctuation

Meets Threatened, B1ab(iii)+2ab(iii).

The EOO of 448 km² and the IAO of 40 km² are below the threshold for Endangered but the population occurs at > 5 locations, is not severely fragmented and does not undergo extreme fluctuations. However, it meets the criteria for Threatened because there is an inferred continuing decline in the extent of habitat, and it occurs at only seven locations.

C: Small and declining number of mature individuals

Meets Threatened, C2a(i).

The population of mature individuals (1,220 to 1,370+) is below the threshold for Endangered, however other sub-criteria are not met. All subpopulations are well below 1,000 mature individuals, and there is an inferred continuing decline in mature individuals due to habitat loss.

D: Very small or restricted population

Not applicable.

The population of 1,220 to 1,370+ mature individuals is above the threshold for Threatened (criterion D1). The IAO of 40 km² exceeds the guideline of 20 km² for Threatened (criterion D2) and, with the occurrence at seven locations, the susceptibility to effects of stochastic storm events impacting the population significantly within a very short time is reduced.

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

(2023)

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

Current classification:

Trillium hibbersonii (T.M.C. Taylor and Szczawinski) D. O’Neill and S.B. Farmer

Class: Liliopsida

Order: Liliales

Family: Melanthiaceae

Genus: Trillium L.

Species: Trillium hibbersonii

Subspecies in Canada: none

Common names:

English: Hibberson’s Trillium, Dwarf Trillium, Dwarf Western Trillium (VASCAN 2022)

French: Trille de Hibberson (VASCAN 2022)

Synonyms and notes:

Trillium ovatum var. hibbersonii (T.M.C. Taylor and Szczawinski) G.W. Douglas and Pojar

Trillium ovatum forma hibbersonii (Hibberson 1938) (Holotype UBC: V73131)

Hibberson’s Trillium was first collected from Boat Basin (Rae Lake subpopulation) in 1938 by Jack Arthur Hibberson (Holotype UBC 73131). In 1968, it was published as Trillium hibbersonii in Rare Wild Flowers of North America (Wiley 1968), but the name was declared to be an invalid nomen nudum by Taylor and Szczawinski (1974), because it did not include a Latin description and did not cite a nomenclatural type (Taylor and Szczawinski 1974; O’Neill 1995; O’Neill et al. 2020). In 1975, Taylor and Szczawinski (1974) reviewed the taxonomic status and published the taxon as Trillium ovatum forma hibbersonii, believing that it forms an intergrading complex with Western Trillium (Trillium ovatum) (Taylor and Szczawinski 1974). The name T. ovatum var. hibbersonii was subsequently proposed by Douglas and Pojar (2001), who also considered it a dwarf variant of T. ovatum.

A review of cytology and morphology and a flavonoid analysis of wild and cultivated plants indicated that Hibberson’s Trillium should be raised to specific status (O’Neill 1995). According to O’Neill et al. (2020), the data obtained by Lampley et al. (unpublished in O’Neill et al. 2020) suggest that this is not only a full species, but a member of a different Trillium clade than T. ovatum. Further verification is required to confirm the relational status to other Trillium species (Allen pers. comm. 2023).

Hibberson’s Trillium maintains its short stature when planted in gardens, regardless of nutrient and soil conditions (Guppy 1968; O’Neill 1995; Douglas and Pojar 2001); gardeners have long believed it to be a distinct species (Guppy 1968; Ware 2014). Plants grown from seed collected from a single whitish flowering specimen collected at Sydney Inlet resulted in plants with pale pink flowers, and there were no colour forms that were transitional to Western Trillium (Roemer 2015). Morphological intermediates with Western Trillium have not been observed at the University of British Columbia native plant garden, despite the spatial proximity of the two species for 19 years; furthermore, crosses between Western and Hibberson’s Trillium do not produce viable offspring (O’Neill 1995). However, morphological intermediates exist in the wild, with some plants reaching a larger stature (Batten pers. obs. 2014).

Description of wildlife species

Hibberson’s Trillium is a small (10 to 27 cm) perennial herb that grows from a stout, fleshy rhizome (Figure 1) (Douglas et al. 2001, 2002; O’Neill 1995). Mature individuals bear three stem leaves in a whorl below the flower. Leaves are broadly ovate, unstalked and with smooth margins. Leaf blades are 3.3 to 5.3 cm long and 1.3 to 2.5 cm wide (O’Neill 1995; Lomer pers. comm. 2019 in Penny 2019). There are no basal leaves. The terminal flowers are borne on a short pedicel and have three pink petals (rarely white with pale pink tinge, but darkening to pink when dried) (Figures 2 and 3) that are offset with three green, fully divided sepals. The seeds develop in an egg-shaped capsule (O’Neill 1995; Douglas et al. 2001, 2002).

Figure 1. Illustration of Hibberson’s Trillium (reprinted with permission from Douglas et al. 2002).

Figure 2. Hibberson’s Trillium with scale bar in cm. Photo: C. Maslovat (April 9, 2022, Clanninick Creek).

Figure 3. Flowering Hibberson’s Trillium showing pink venation on petals. Photo: R. Batten (April 14, 2014, Rae Lake)

The only other Trillium species in British Columbia, Western Trillium, occurs from southern British Columbia (including Vancouver Island) south to California and east to Alberta, Montana, Wyoming and Colorado (CPNWH 2022; NatureServe 2022). In British Columbia, Western Trillium is larger (20 to 45 cm tall) than Hibberson’s Trillium and has flowers that are white when they open, often becoming pink as they age (Douglas et al. 2001; Douglas and Pojar 2001). Western Trillium is found in rich soils in moist, shady sites under the forest canopy (Douglas et al. 2001; Douglas and Pojar 2001), while Hibberson’s Trillium occurs in seasonally wet seepage areas on rocky slopes—and, in one locality, in a creek bed—and is restricted to the northern and central portions of the west coast of Vancouver Island (Douglas and Pojar 2001; O’Neill et al. 2020).

Designatable units

There are no recognized subspecies/varieties or discrete/evolutionary significant populations to be recognized as designatable units for the Canadian population. Consequently, the occurrence of Hibberson’s Trillium in Canada is considered as one designatable unit.

Recognized subspecies or varieties in Canada: None

Designatable units (DUs): One

Special significance

Hibberson’s Trillium is endemic to Canada. The species’ large showy flowers and diminutive stature have inspired interest in it as a horticultural species for alpine rock gardens (Guppy 1968; Douglas and Pojar 2001; Clarke 2006; Whitehead 2009; Ware 2014). Offspring from plants collected in 1938 by Hibberson have been widely grown by gardeners (Guppy 1968; Taylor and Szczawinski 1974). Hibberson’s Trillium can be propagated ex situ from seed and offsets (Guppy 1968), but trilliums are difficult to propagate, so supplying sufficient plants to meet the horticultural demand may be challenging (Case and Case 1997 in Chauhan et al. 2019; Klest 2002). Fraser’s Thimble Farms on Saltspring Island, B.C., has offered Hibberson’s Trillium for sale in the past, but it is not currently available (Fraser’s Thimble Farms 2022).

Species in the Trillium genus are rich in bioactive phytochemicals and are used extensively in traditional medicine (Rahman et al. 2017; Chauhan et al. 2018, 2019; Rathore et al. 2020). Over 40 secondary metabolites have been isolated in the genus, including steroids, saponins and flavonoids that may have pharmacological applications due to their anti-cancer, anti-fungal, anti-inflammatory and analgesic properties (Rahman et al. 2017; Chauhan et al. 2019). The leaves of other Trillium species are eaten raw or cooked as a pot herb (Alternative Nature Online Herbal 2022; Deane 2022; Edible Wild Food 2022).

Trillium seeds have lipid-rich structures (elaiosomes) that are eaten by insects, gastropods and mammals, which help disperse the seeds (Mesler and Lu 1983; Ohara and Higashi 1987; Ohara 1989; Jules 1996; Kalisz et al. 1999; Miller and Kwit 2018). Deer eat the seed pods and may also disperse the seeds (Vellend et al. 2003).

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 occurrences. 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, Hibberson’s Trillium is important to Indigenous Peoples who recognize the interrelationships of all species within the ecosystem.

Distribution

Global range

Hibberson’s Trillium is endemic to British Columbia’s Vancouver Island (Figure 4).

Figure 4. Global distribution of Hibberson’s Trillium (map prepared by Alain Filion).

Canadian range

The entire global range of Hibberson’s Trillium is in Canada; it is known from seven subpopulations in the northern and central portions of the west coast of Vancouver Island (Figure 4). The most northerly subpopulation is along Clanninick Creek off Kyuquot Sound, while two subpopulations are near Hesquiat Lake, and four are located close to Sydney Inlet. Western Vancouver Island is extremely remote and difficult to access, and the survey coverage for this species has significant gaps, including vast areas that may contain suitable habitat.

Search effort has been extremely limited since the species was first recorded at Rae Lake by Hibberson in 1938. The Rae Lake subpopulation was re-surveyed in 1947 and more recently in 1981, 1997, 2001 and 2014, but detailed counts were not performed (Table 1).

The Clanninick Creek subpopulation was documented in 1958 by Taylor and Szczawinski. In the 1970s, a loose piece of turf containing a single Hibberson’s Trillium plant was found washed down to the estuary by William van Dieren; the plant was planted in a pot by Oluna Ceska (Roemer 2015). This subpopulation was re-confirmed in 2022 during the fieldwork prior to this status report (Table 1).

The Hesquiat Lake subpopulation was first documented by Adolf and Oluna Ceska in 1981. In 2001, a BC Parks officer discovered a new subpopulation at Sydney Inlet, which was confirmed by Hans Roemer, A. Ceska and O. Ceska the same year.

In 2019, Penny, Lomer, McClaren, Grandbois and Patterson documented three new subpopulations (two at Sydney Inlet and one at Pretty Girl Cove), and the subpopulations at Sydney Inlet and Hesquiat Lake were re-surveyed the same year (Penny 2019). The 2019 survey increased the number of known subpopulations by 63%, suggesting that more survey effort is required to determine the species’ full distribution and abundance (Penny 2019). During surveys in 2023, an additional eight sites were found within 1 km of the original Sydney Inlet subpopulation (Dunning et al. 2023). Owing to the large expanse of unsurveyed area, further search effort will likely find new subpopulations.

Population structure

For Hibberson’s Trillium, the COSEWIC term “subpopulation,” defined as “geographically or otherwise distinct groups in the population between which there is little demographic or genetic exchange” (COSEWIC 2019), corresponds well to an element occurrence as identified in NatureServe’s (2020) habitat-based plant element occurrence delimitation standards, which require a default separation distance of 1 km except in riparian corridors, dynamic landscape mosaics and continuous apparently suitable habitat. There has been no research on genetic structure within the population.

Extent of occurrence and area of occupancy

The Extent of Occurrence (EOO) and Index of Area of Occupancy (IAO) were estimated by the COSEWIC Secretariat based on all known records, as all subpopulations are extant.

Current EOO

The EOO in Canada is 448 km², calculated using a minimum convex polygon that encompasses the known records during the 2014 to 2022 period.

Current IAO

The IAO in Canada is 40 km², calculated using a 2 km x 2 km grid drawn over known records during the 2014 to 2022 period. Although it seems likely that additional sites will be found, the upper range for IAO is not known but is certainly less than 2,000 km², based on our knowledge of the range and the habitat.

Fluctuations and trends in distribution

No long-term monitoring has been carried out, and reliable repeat counts of the number of mature individuals have not been performed at any of the known subpopulations; therefore, the available data are not sufficient to infer trends in distribution. All the previously documented subpopulations are still extant, so there have been no observed declines in EOO or IAO. A recent increase in the number of known subpopulations is the result of an expanded search effort, and does not reflect a genuine increase in population size.

Biology and habitat use

Life cycle and reproduction

Information on the biology and ecology of Hibberson’s Trillium is limited. The information presented below has been compiled primarily from research on related species, the small number of studies on Hibberson’s Trillium, grey literature and the report writers’ personal observations.

Trilliums reach maturity in 4 to 20 years depending on the species and growing conditions; the age of the plant can be determined by counting the annual rhizome scars (Ohara 1989; Hanzawa and Kalisz 1993; Case and Case 1997 in NatureServe 2022). In the wild, the average reproductive age of White Trillium (T. grandiflorum) was 23 years, with a minimum reproductive age of 17 years (Hanzawa and Kalisz 1993). In a garden setting, Hibberson’s Trillium flowered three and four years after being sown in pots (Carolyn 2015), but age to maturity in the wild is not known. Other Trillium species can reproduce both vegetatively through rhizomes and sexually, although asexual reproduction is uncommon or absent in many species (Ohara 1989; Hanzawa and Kalisz 1993; Chauhan et al. 2019). Horticulturally, Hibberson’s Trillium has been grown from offsets (Guppy 1968; Miskelly pers. comm. 2023), but it is not known if asexual reproduction occurs in the wild.

A member of a rock garden forum suggested that, in a garden setting, Hibberson’s Trillium can live for at least 35 years (Whitehead 2009), but it is possible that plants are persisting in the same locality from offsets. The average age of parents in the population (generation time) for Hibberson’s Trillium is estimated to be 10 to 20 years, which is greater than the minimum of three years to maturity and less than the maximum suggested age of 35 years.

Hibberson’s Trillium blooms in early April. Pollinators are discussed in Interspecific interactions. It is unknown how many seeds are produced per plant, and there have been no studies on juvenile and adult survival rates or recruitment. White Trillium seedlings develop roots in the first growing season, with the cotyledon emerging in the second growing season and a single leaf emerging in the third growing season (Hanzawa and Kalisz 1993), while, in other species, seedlings emerge within the year (Case and Case 1997 in Chauhan et al. 2019). It is likely that Hibberson’s Trillium emerges after a single year, because only a single cold period is required; in contrast, Western Trillium exhibits double dormancy, requiring two winters and one summer for germination (O’Neill 1995). When planted in pots, Hibberson’s Trillium seeds germinated the first spring after sowing and produced linear cotyledons (Leena 2019).

Trillium stems emerge annually from the rhizome in the spring, with usually only one stem produced per year (Hanzawa and Kalisz 1993; Case and Case 1997 in Chauhan et al. 2019). Following the cotyledon stage, there are three stages in the Trillium life cycle: one-leaf vegetative, three-leaf vegetative and three-leaf reproductive. A minimum size and/or age must be attained for flowering to occur (Ohara 1989; Hanzawa and Kalisz 1993; Chauhan et al. 2018). Not all plants above the size threshold for reproduction flower each year (Hanzawa and Kalisz 1993).

Hibberson’s Trillium is diploid (2n = 10) (O’Neill 1995). In other Trillium species, seeds are more likely to be produced from cross-fertilization, whereas self-fertilized seeds may exhibit poor germination, establishment and growth (Kalisz et al. 1999; Irwin 2000).

Habitat requirements

Hibberson’s Trillium occurs in the Coastal Western Hemlock zone (CWH), in the very wet hypermaritime biogeoclimatic subzone (CWHvh) and nearby very wet maritime biogeoclimatic subzone (CWHvm) (habitat description in Table 2; Figures 5 to 7). Most subpopulations are found at low elevations (as low as 3 m; Specimen UBC V250699), next to the ocean or a lake, but plants have been discovered at elevations as great as 340 m (Penny 2019; BC CDC 2022). Soils are thin and poorly developed (Penny 2019; O’Neill et al. 2020; Dunning et al. 2022; Maslovat and Batten 2022), sometimes occurring over talus (Specimen UBC V250698).

^a Life Stage: Stage of the life cycle of the species (for example, seed, egg, seedling, juvenile, larva, pupa, adult)

^b Habitat function: How the habitat supports a life-cycle process of the species (for example, habitat that supports spawning, breeding, denning, nursery, rearing, feeding/foraging, migration, flowering, fruiting, seed dispersing, germinating, seedling development)

^c Habitat: The structural or biological features of the area or type of site needed for a species to carry out its life processes

^d Habitat details: Detailed information such as measurable properties or characteristics of the habitat

Figure 5. Hibberson’s Trillium habitat at Rae Lake. Photo: R. Batten (April 14, 2014, Rae Lake).

Figure 6. Aerial view of Rae Lake, showing the limited rock outcrop habitat in the landscape. Photo: R. Batten (April 14, 2014, Rae Lake).

Figure 7. Hibberson’s Trillium habitat at Sydney Inlet. Photo: E. McClaren (April 16, 2019, Sydney Inlet).

For six of the subpopulations, the habitat ranges from east to southwest facing, from full sun to semi-shade. Sites include open rocky ledges, outcrops and cliffs, crevices of rock walls and partly exposed rocks with seasonal seepage (Penny 2019). Seepages range from moist to fully saturated by falling water in April (Dunning et al. 2023). At Sydney Inlet Provincial Park, plants growing in semi-shade were less vigorous than plants growing in full sun (Dunning et al. 2023).

The Clanninick Creek subpopulation is found in a riparian area next to the creek, in areas that are inundated during peak flows. The plants grow in small clefts in the rock with soil deposits, on mossy banks or steep cliffs on the side of the creek or on boulders in the centre of the creek (Dunning et al. 2022; Maslovat and Batten 2022). Sand deposits are 2.5 to 4 cm deep and are overgrown by moss, primarily Streamside Moss (Scouleria aquatica) (Dunning et al. 2022; Maslovat and Batten 2022). The sites are shaded by dense Sitka Spruce (Picea sitchensis) and Western Red Cedar (Thuja plicata) stands and by deep canyon walls, with plants receiving direct sunlight only at midday (Dunning et al. 2022; Maslovat and Batten 2022). In 2022, one of the sites that did not receive direct sunlight had no flowering plants (Dunning et al. 2022).

Movements, migration, and dispersal

Hibberson’s Trillium seeds have an elaiosome (O’Neill 1995), a lipid-rich attachment that attracts animals and serves as a dispersal mechanism. In other Trillium species, ants (Ohara and Higashi 1987; Kalisz et al. 1999; Miller and Kwit 2018) and wasps (Jules 1996) carry the seeds to their nests, eat the elaiosomes and discard the seeds. Ground beetles (Carabidae) (Ohara and Higashi 1987; Ohara 1989) and the Pacific Banana Slug (Ariolimax columbianus) (Mesler and Lu 1983) also eat the elaisomes, facilitating short-distance seed transportation. Trillium seeds are also eaten by deer, and remain viable in the animals’ digestive tracts, possibly enabling long-distance dispersal (Vellend et al. 2003).

Studies of dispersal in Western Trillium show dispersal over limited distances, with 67% of recruitment occurring within 1 m of a potential parent (Kahmen and Jules 2005). Experimental studies have observed ants carrying the seeds of other Trillium species up to 10 m from the parent plant, with the average dispersal distance ranging from 0.5 m to 2.4 m (Kalisz et al. 1999), while yellow jackets (Vespula spp.) carried seed an average of 1.4 m (Zettler et al. 2001). Hibberson’s Trillium could also be gravity dispersed, in the case of plants on ledges and cliff faces. It is unknown if Trillium seeds are buoyant and if dispersal occurs by water.

Interspecific interactions

Predators and competitors

Instances of herbivory on Hibberson’s Trillium occur, possibly by the American Black Bear (Ursus americanus); in 2014, many freshly grazed plants were observed in the Rae Lake population (Roemer pers. comm. 2018 in BC CDC 2018). Trilliums are a preferred food of deer, which eat both the leaves and flowers, leaving an unproductive stem that does not re-sprout until the following year (Jules 1998; Knight 2003; Leege et al. 2010). Herbivory can result in regression to a vegetative stage in the next season and decreased reproductive success (Knight 2003; Leege et al. 2010). Deer are not hyper-abundant on the west coast and do not impact Hibberson’s Trillium beyond typical natural levels.

Other interactions

No studies have been carried out on the pollinators of Hibberson’s Trillium, but pollinators of other Trillium species include flies, bees and beetles (Case and Case 1997 in Chauhan et al. 2019; Jules 1998; Irwin 2000). A beetle in the family Chrysomelidae was observed on Hibberson’s Trillium plants at the University of British Columbia Botanical Garden (O’Neill 1995), and several species of Diptera were observed pollinating Hibberson’s Trillium at Clanninick Creek (Figure 8; Dunning et al. 2022).

Ants, wasps, ground beetles, Pacific Banana Slug and deer are known dispersal agents for seeds of other Trillium species (read Movements, Migration, and Dispersal).

Figure 8. Pollinator on Hibberson’s Trillium at Clanninick Creek. Photo: J. Dunning (April 16, 2022, Clanninick Creek).

Physiological, behavioural, and other adaptations

Hibberson’s Trillium has high levels of anthocyanin, which may provide protection from ultraviolet radiation (O’Neill 1995). Numerous secondary metabolites are found in other Trillium species (Rahman et al. 2017; Chauhan et al. 2019; Rathore et al. 2020). The physiological adaptations and potential adaptive advantages for the plants are not known.

Limiting factors

Limiting factors are generally not human-induced and include intrinsic characteristics that make the species less likely to respond to conservation efforts. Limiting factors may become threats if they result in population decline. The main limiting factors for Hibberson’s Trillium are the scarcity of suitable habitat and its distribution in isolated patches, low fecundity rates and limited mechanisms for long-distance dispersal. Other Trillium species are susceptible to climate-change-related impacts because they have low fecundity and limited recruitment (Chauhan et al. 2019). There have been no studies on Hibberson’s Trillium fecundity and recruitment.

Population sizes and trends

Data sources, methodologies, and uncertainties

The population size was calculated by summing the most recent count data for all subpopulations. Five of the seven subpopulations were surveyed in 2019 during fieldwork conducted by biologists from the B.C. Conservation Data Centre and BC Parks, as well as a biological consultant. The number of flowering mature plants was estimated in the five subpopulations, and two of the subpopulations were re-surveyed in 2023. The Rae Lake subpopulation was not surveyed, but its size was estimated by biologists on an unpaid excursion (so the survey may have been incomplete). In the Clanninick Creek subpopulation, two different surveys were conducted within days of each other, survey routes were compared, and the highest count number was used for population estimates. None of the subpopulations has had consistent monitoring or systematic recounts, so no data are available for estimating or inferring population trends.

Abundance

Hibberson’s Trillium has probably always been rare because of the limited availability of habitat in its range. It is known from seven subpopulations collectively supporting an estimated total of 1,220 to 1,370 mature flowering individuals (Table 1). It is possible some of the non-flowering plants were mature, but did not flower in the survey year; however, this is impossible to determine without excavation, so the number of flowering plants is presumed to be the number of mature individuals. The estimated number of plants per subpopulation ranges from 20 to 400 to 450 flowering plants, plus non-flowering plants. Although some additional sites will likely be found, the total number of mature individuals is expected to be well below 10,000.

Fluctuations and trends

No monitoring or population modelling data are available in order to determine fluctuations and trends. Hibberson’s Trillium is a long-lived species and, in the absence of habitat destruction, subpopulation numbers are expected to remain relatively stable over time. The presence of plants at Rae Lake since 1938 and at Clanninick Creek since 1958 suggests that the subpopulations are viable and persistent over the long term. Subpopulations have also persisted at Hesquiat Lake since 1981 and at Sydney Inlet since 2001.

Continuing decline^{Footnote 2} in number of mature individuals

Although there is no direct evidence of a continuing decline in the number of mature individuals due to the lack of consistent surveys, this continuing decline is likely as a result of the ongoing threats of logging and landslides. It is also possible that subpopulations have been lost due to these activities before these subpopulations were documented.

Evidence for past decline (3 generations or 10 years, whichever is longer) that has either ceased or is continuing (specify)

There is no evidence for a past decline in the number of mature individuals, due to the lack of consistent surveys.

Evidence for projected or suspected future decline (next 3 generations or 10 years, whichever is longer, up to a maximum of 100 years)

There is no evidence for a projected future decline in the number of mature individuals, due to the lack of consistent surveys. Future decline is suspected as a result of ongoing threats.

Long-term trends

There are no data on long-term trends due to a lack of repeated surveys. Habitat destruction associated with logging is ongoing on Vancouver Island, and it is inferred from these habitat trends that subpopulations may be destroyed before they are recorded.

Population fluctuations, including extreme fluctuations

There is no evidence of fluctuations in numbers of mature individuals or subpopulations due to the lack of consistent surveys. The recent increase in the number of known subpopulations results from a greater search effort rather than a genuine increase in population size. It is inferred that extreme fluctuations in the number of plants are unlikely, because individuals are presumed to be long-lived and all known subpopulations have persisted since they were first observed.

Severe fragmentation

Although there is a lack of long-term monitoring for this species, all known subpopulations have persisted since they were first recorded, suggesting that habitat patches are of sufficient size to support viable subpopulations. Rock outcrops or cliffs with seepage and creek habitats are naturally rare in the landscape and are isolated in dense coniferous forests (Figure 6). Separation distances between habitat patches are greater than the species’ dispersal potential, given its limited dispersal mechanisms (primarily insects and gastropods).

Rescue effect

There is no possibility of rescue because Hibberson’s Trillium is endemic to Canada and restricted to Vancouver Island, British Columbia.

Threats

Historical, long-term, and continuing habitat trends

The survey coverage and the data available are insufficient to assess habitat trends. Habitat extent and quality are believed to have declined due to ongoing logging, which may have destroyed suitable habitat and possibly undocumented subpopulations. On Vancouver Island, 243,000 ha of forest was logged between 2004 and 2015, of which 100,000 ha was old growth (Wieting 2016). All known subpopulations occur in riparian areas or on rocky ledges, outcrops or cliff habitat that would not be directly impacted by logging; however, timber harvesting and road building in adjacent areas may indirectly cause habitat destruction through landslides or altered hydrology.

Current and projected future threats

Hibberson’s Trillium is vulnerable to the cumulative effects of various threats. The nature, scope, and severity of these threats are assessed in Appendix 1, following the IUCN-CMP (International Union for the Conservation of Nature – Conservation Measures Partnership) unified threats classification system (see Salafsky et al. 2008 for definitions and Master et al. 2012 for guidelines). The threat assessment process consists of assessing the impacts of each of 11 main categories of threats and their subcategories, based on the scope (proportion of population exposed to the threat over the next 10‑year period), severity (predicted population decline within the scope during the next 10 years or 3 generations, whichever is longer, up to ~100 years) and timing of each threat. The overall threat impact is calculated by taking into account the separate impacts of all threat categories, and can be adjusted by the species experts participating in the threats evaluation.

The overall threat impact for Hibberson’s Trillium is considered Medium - Low, corresponding to an anticipated further decline of between 1% and 30% (Low indicates a range of 1 to 10% and Medium, of 3 to 30%) over the next three generations (30 – 60 years). These values are to be interpreted with caution, as they may be based on subjective information such as expert opinion, although efforts have been made to corroborate the scores with the available studies and quantitative data.

The primary threats to Hibberson’s Trillium are 

Biological resource use: logging and wood harvesting (IUCN 5.3; overall threat impact medium - low)

All known Hibberson’s Trillium subpopulations occur on open rocky ledges, outcrops or cliff habitat or in riparian areas, and are not likely to be directly impacted by timber harvesting. However, timber harvesting or access road construction in adjacent areas may alter seepage patterns, cause erosion, or inadvertently destroy all or part of a subpopulation. Wood harvesting activities are known to increase landslide frequency, especially in association with extreme precipitation events; this is evaluated under threat 10.3 Avalanches/Landslides.

Four of the seven subpopulations occur in B.C.’s provincial parks, which are protected from wood harvesting but could be impacted by logging on upslope Crown land. The remaining three subpopulations (53% of the total population) occur on provincial Crown land, which could be directly impacted by wood harvesting.

The Clanninick Creek subpopulation may be vulnerable to erosion associated with logging, because the plants are next to a creek and are submerged during high water events. However, the plants have persisted at this site for over 60 years and appear to be able to survive under water after heavy spring rains. They grow in the compacted sand in boulder crevices, where they are anchored by long roots, so they are unlikely to be washed away. Clanninick Creek Ecological Reserve is upslope of the subpopulation and is protected from logging.

There is no information on the possible timing of harvesting. However, it is unlikely that harvesting would occur in all three unprotected subpopulations at the same time and, even if harvesting or habitat destruction related to harvesting activities occurred, some plants would likely survive. It is possible that other undocumented subpopulations exist in the suitable forest habitat in the region.

Geological events: avalanches/landslides (IUCN 10.3; overall threat impact medium - low)

Tsunamis and landslides associated with geological events could affect this species, but the impact is difficult to determine (Penny 2019). Landslides do occur naturally on the west coast of Vancouver Island, and their frequency increases with forest harvesting. A landslide in Sydney Inlet Provincial Park from natural causes opened up a large tract of land and exposed new cliff faces (Dunning et al. 2023). Landslides occur very infrequently in natural situations and only affect small areas; however, if one occurred in the vicinity of Hibberson’s Trillium, it could have a serious impact.

In the nearby Artlish River watershed, the natural rate of landslides appears to be about one per year. The average rate post-logging is 3.25 landslides per year, or about a threefold increase in frequency (Guthrie 2002). Landslides have occurred on the slopes above Hesquiat Lake and, in 2018, seven major slides occurred on Mount Seghers, filling the lake with woody debris; it is unclear if the slides were caused by logging 40 years prior (Titian 2018). At Hesquiat Lake, Hibberson’s Trillium grows on rock outcrops close to the lake and could be dislodged by woody debris and slide events in areas across from and north of the previous landslides (Penny 2019).

Landslides may also increase in frequency and size with the increasing severity and frequency of storms associated with climate change.

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

This threat category applies to subpopulations in protected areas that are not subject to increased landslide activity due to logging, but that could be affected by the impacts of increasingly frequent storms and flooding associated with climate change, including storm surges along the seashore.

Most subpopulations occur in areas with steep terrain that is vulnerable to erosion from storms and flooding associated with extreme precipitation events. The west coast of Vancouver Island is subject to naturally occurring, variable, high precipitation events; however, these extreme events appear to be increasing in frequency and intensity along with climate change.

The sea-level rise associated with storms may also be a concern for some subpopulations that are at low elevations (Penny 2019).

Number of threat locations

There are seven element occurrences, as defined by the B.C. Conservation Data Centre using the default minimum separation distance of 1 km (NatureServe 2020), corresponding to the seven subpopulations presented in this status report. Based on the threat evaluation, each of these represents a geographically distinct location where a single threatening event, such as a landslide, can rapidly affect all individuals present (Table 3). The number of clumps of plants in each location ranges from one to ten, and it is not possible to consider multiple threat locations in any subpopulation due to the spatial separation of threats. There is no information on trends or fluctuations in the number of locations.

Protection, status, and recovery activities

Legal protection and status

Hibberson’s Trillium currently has no legal protection or status, and is not listed under the Species at Risk Act. Although Western Trillium is protected under the Dogwood, Rhododendron and Trillium Protection Act, Hibberson’s Trillium is not, even after it was elevated to specific status (King’s Printer 1998).

The species is not listed under the Convention on International Trade in Endangered Species (CITES 2022). The International Union for Conservation of Nature currently considers Hibberson’s Trillium to be a sub-taxon of Western Trillium, which is designated as Least Concern on the Red List (Meredith et al. 2020, 2022). Following the elevation of Hibberson’s Trillium to the species level, it will likely be categorized as Vulnerable under criterion D1 (very small or restricted population) (Meredith et al. 2022). The Red List assessment was carried out prior to the findings of the 2019 fieldwork.

Non-legal status and ranks

Provincially, Hibberson’s Trillium is ranked S3 (Vulnerable) by the B.C. Conservation Data Centre and is ranked N3 (Vulnerable) nationally (NatureServe 2022). In 2019, it was globally ranked G3 (Vulnerable) based on the NatureServe rank calculator (NatureServe 2022).

Land tenure and ownership

Four of the known Hibberson’s Trillium subpopulations are protected from development due to their location in B.C. provincial parks; however, the remaining three subpopulations are on unsurveyed provincial Crown land (Table 3).

Information sources

References cited

Allen, G., pers. comm. 2023. In-person conversation with R. Batten. February 2023. Professor, Biology, University of Victoria, Victoria, B.C.

Alternative Nature Online Herbal. 2022. Trilliums, Birthroot, Beth Root. Website: https://altnature.com/gallery/trilliums.htm [accessed August 2022].

Batten, R., pers. obs. 2014. Botanist, B.C. Conservation Data Centre, Ecosystems Branch, B.C. Ministry of Environment and Climate Change Strategy. Victoria, B.C.

B.C. Conservation Data Centre (BC CDC). 2018. Occurrence Report Summary, Shape ID 42822, Hibberson’s Trillium. B.C. Ministry of Environment. Website: http://maps.gov.bc.ca/ess/hm/cdc [accessed August 2022].

B.C. Conservation Data Centre (BC CDC). 2022. BC Species and Ecosystems Explorer. Website: https://a100.gov.bc.ca/pub/eswp/search.do [accessed August 2022].

Carolyn. 2015. Re: Trillium 2015. Post on Scottish Rock Garden Club Forum. April 12, 2015. Website: https://www.srgc.org.uk/forum/ [accessed August 2022].

Case, F.W., and R.B. Case. 1997. Trilliums. Timber Press, Portland, Oregon. 285 pp.

Chauhan, H.K., A.K. Bisht, I.D. Bhatt, A. Bhatt, and D. Gallacher. 2019. Trillium – toward sustainable utilization of a biologically distinct genus valued for traditional medicine. The Botanical Review 85:252-272

Chauhan, H.K., A.K. Bisht, I.D. Bhatt, A. Bhatt, D. Gallacher, and A. Santo. 2018. Population change of Trillium govanianum (Melanthiacea) amid altered Indigenous harvesting practices in the Indian Himalayas. Journal of Ethnopharmacology 213:302-310.

Clarke, G. 2006. Trillium. Horticulture Week; Teddington: 18-19. August 10, 2006.

Consortium of Pacific Northwest Herbaria Specimen Database (CPNWH). 2022. Website: https://www.pnwherbaria.org [accessed July 2022].

Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). 2022. Website: https://www.speciesplus.net [accessed July 2022].

Deane, G. 2022. Trillium trifecta. Eat the weeds and other things too. Website: https://www.eattheweeds.com/trillium-trifecta/ [accessed August 2022].

Douglas, G.W., D.V. Meidinger, and J. Pojar (eds.). 2001. Illustrated Flora of British Columbia, Volume 6: Monocotyledons (Acoraceae Through Najadaceae). B.C. Ministry of Environment, Lands and Parks and B.C. Ministry of Forests, Victoria, British Columbia. 361 pp.

Douglas, G.W., D.V. Meidinger, and J. Pojar (eds.). 2002. Illustrated Flora of British Columbia, Volume 8: General Summary, Maps and Keys. B.C. Ministry of Sustainable Resource Management and B.C. Ministry of Forests, Victoria, British Columbia. 457 pp.

Douglas, G.W., and J. Pojar. 2001. Trillium ovatum Pursh variety hibbersonii (Taylor et Szczawinski) Douglas et Pojar, variety nova. Canadian Field-Naturalist 115:353.

Dunning, J., S. Johnson, C. Kreutzenstein, and I. Cruickshank. 2023. Expanding the range of Trillium hibbersonii in Sydney Inlet, B.C. Unpublished report.

Dunning, J., P. Spriggs, S. Johnson, and C. Kreutzenstein. 2022. Clanninick Creek Field Trip Report: Searching for Trillium hibbersonii. Unpublished report.

Edible Wild Food. 2022. Red Trillium Trillium erecta. Website: https://www.ediblewildfood.com/red-trillium.aspx [accessed August 2022].

Farmer, S.B. 2006. Phylogenetic analyses and biogeography of Trilliaceae. Aliso: A Journal of Systematic and Floristic Botany: 22(1):Article 45. Website: https://scholarship.claremont.edu/aliso/vol22/iss1/45 [accessed July 2022].

Fraser’s Thimble Farms. 2022. Catalogue. Website: http://www.thimblefarms.com [accessed July 2022].

Guppy, A.G. 1968. The rare Trillium of Vancouver Island. American Rock Garden Society Bulletin 26:119-120.

Guthrie, R. 2002. Landslide frequency and logging on Vancouver Island: an analog showing varied yet significant changes. Pp. 70-79, in P. Jordan and J. Orban ( eds.). Terrain Stability and Forest Management in the Interior of British Columbia. Proceedings of Workshop, May 23-25, 2001, Nelson, B.C., B.C. Ministry of Forests, Research Branch. Technical Report 003.

Hanzawa, F.M., and S. Kalisz. 1993. The relationship between age, size, and reproduction in Trillium grandiflorum (Liliaceae). American Journal of Botany 80:405‑410.

International Union for Conservation of Nature (IUCN). 2022. The IUCN Red List of Threatened Species. Version 2021-3. Website: https://www.iucnredlist.org [accessed July 2022].

Irwin, R.E. 2000. Morphological variation and female reproductive success in two sympatric Trillium species: evidence for phenotypic selection in Trillium erectum and Trillium grandiflorum (Liliaceae). American Journal of Botany 87(2):205-214.

Jules, E.S. 1996. Yellow jackets (Vespula vulgaris) as a second seed disperser for the myrmecochorous plant, Trillium ovatum. The American Midland Naturalist 135:367‑‑369.

Jules, E.S. 1998. Habitat fragmentation and demographic change for a common plant: Trillium in old-growth forest. Ecology 79:1645-1656.

Kahmen, A., and E.S. Jules. 2005. Assessing the recovery of a long-lived herb following logging: Trillium ovatum across a 424-year chronosequence. Forest Ecology and Management 210:107-116.

Kalisz, S.,F.M. Hanzawa, S.J. Tonsor, D.A. Thiede, and S. Voigt. 1999. Ant-mediated seed dispersal alters pattern of relatedness in a population of Trillium grandiflorum. Ecology 80:2620-2634.

King’s Printer. 1998. Dogwood, Rhododendron and Trillium Protection Act. [RSBC 1996] Chapter 100. Website: https://www.bclaws.gov.bc.ca/civix/document/id/consol2/consol2/96100_01 [accessed March 2023].

Klest, S.M. 2002. Propagation protocol for Western Trilliums. Native Plants Journal 3:22-23.

Knight, T.M. 2003. Effects of herbivory and its timing across populations of Trillium grandiflorum (Liliaceae). American Journal of Botany 90:1207-1214.

Leege, L.M., J.S. Thompson, and D.J. Parris. 2010. The responses of rare and common Trilliums (Trillium reliquum, T. cuneatum, and T. maculatum) to deer herbivory and invasive honeysuckle removal. Castanea 75:433-443.

Leena. 2019. Re: Trillium 2019. Post on Scottish Rock Garden Club Forum. April 13, 2019. Website: https://www.srgc.org.uk/forum/ [accessed August 2022].

Maslovat, C., and R. Batten. 2022. Field Work Summary Report, Hibberson’s Trillium (Trillium hibbersonii). Unpublished report prepared for COSEWIC. 11 pp.

Master, L.L., D. Faber-Langendoen, R. Bittman, G.A. Hammerson, B. Heidel, L. Ramsay, K. Snow, A. Teucher, and A. Tomaino. 2012. NatureServe conservation status assessments: factors for evaluating species and ecosystems risk. NatureServe, Arlington, Virginia.

Meredith, C., A. Frances, A. Highland, L. Oliver, A. Floden, L.L. Gaddy, W. Knapp, D. Leaman, S. Leopold, T. Littlefield, R. Raguso, E.E. Schilling, A. Schotz, A. Walker, and K. Wayman. 2022. The Conservation Status of Trillium in North America. Mt. Cuba Center and New Mexico BioPark Society. Hockessin, Delaware, and Albuquerque, New Mexico. 86 pp.

Meredith, C.R., E. Schilling, and Trillium Working Group. 2020. Trillium ovatum. The IUCN Red List of Threatened Species 2020: e.

Mesler, M.R., and K.L. Lu. 1983. Seed dispersal of Trillium ovatum (Liliaceae) in second-growth redwood forests. American Journal of Botany 70:1460-1467.

Miller, C.N., and C. Kwit. 2018. Overall seed dispersal effectiveness is lower in endemic Trillium species than in their widespread congeners. American Journal of Botany 105:1847-1857.

Miskelly, K., pers. comm. 2023. Telephone conversation with C. Maslovat. April 2023. Owner, Satinflower Nursery, Victoria, British Columbia.

NatureServe. 2020. Biotics5: Habitat-based Plant Element Occurrence Delimitation Guidance. Version 1.0 published October 2004; Revised May 2020. Website: https://www.natureserve.org/sites/default/files/eo_specs-habitat-based_plant_delimitation_guidance_may2020.pdf [accessed July 2022].

NatureServe. 2022. NatureServe Network Biodiversity Location Data accessed through NatureServe Explorer [web application]. NatureServe, Arlington, Virginia. Website: https://www.natureserve.org [accessed July 2022].

Ohara, M. 1989. Life history evolution in the genus Trillium. Plant Species Biology 4:1‑28.

Ohara, M., and S. Higashi. 1987. Interference by ground beetles with the dispersal byants of seeds of Trillium species (Liliaceae). Journal of Ecology 75:1091-1098.

O’Neill, D. 1995. Taxonomic study of Trillium ovatum forma hibbersonii. M.Sc. thesis, University of British Columbia, Vancouver, British Columbia. 102 pp.

O’Neill, D.M., S.B. Farmer, A. Floden, J. Lampley, and E.E Schilling. 2020. Trillium hibbersonii (Melanthiaceae), a phylogenetically distinct species from western North America. Phytotaxa 436:193-195. https://doi.org/10.11646/phytotaxa.436.2.9

Penny, J. 2019. Hibberson’s Trillium surveys for BC Parks. Unpublished report prepared for BC Parks License Plate Program.

Rahman, S., M. Ismail, M. Khurram, I. Ullah, F. Rabbi, and M. Iriti. 2017. Bioactive steroids and saponins of the genus Trillium. Molecules 22:2156. https://doi.org/10.3390/molecules22122156

Rathore, S., S. Walia, R. Devi, and R. Kumar. 2020. Review of Trillium govanianum Wall. ex D. Don: a threatened medicinal plant from the Himalaya. Journal of Herbal Medicine 24:100395.

Roemer, H. 2015. Hibberson’s Trillium – extended chronology. Unpublished report.

Roemer, H., pers. comm. 2018. Email correspondence to BC CDC staff. Botanist, Victoria, British Columbia.

Salafsky, N., D. Salzer, A.J. Stattersfield, C. Hilton-Taylor, R. Neugarten, S.H.M. Butchart, B. Collen, N. Cox, L.L. Master, S. O’Connor, and D. Wilkie. 2008. A standard lexicon for biodiversity conservation: unified classifications of threats and actions. Conservation Biology 22:897-911.

Taylor, T.M.C. and A.F Szczawinski. 1974. Trillium ovatum Pursh forma hibbersonii Taylor et Szczawinski f. nov. Syesis 7:250.

Titian, D. 2018. Heavy November rains cause several landslides in Hesquiaht salmon-bearing lakes. Ha-shilth-Sa. Canada’s oldest First Nation newspaper. Website: https://hashilthsa.com/news/2018-11-27/heavy-November-rains-cause-several-landslides-hesquiaht-salmon-bearing-lakes [accessed August 2022]

VASCAN (Database of Vascular Plants of Canada). 2022. Trillium hibbersonii (T.M.C. Taylor and Szczawinski) D. O’Neill and S.B. Farmer. Website: https://data.canadensys.net/vascan/taxon/32302?lang=en [accessed July 2022].

Vellend, M., J. Myers, S. Gardescu, and P. Marks. 2003. Dispersal of Trillium seeds by deer: implications for long-distance migration of forest herbs. Ecology 84:1067-1072.

Ware, G. 2014. Trillium hibbersonii – the fugitive species of Vancouver Island. Alpine Garden Club of British Columbia Quarterly Bulletin 57(3):71-73.

Whitehead, D. 2009. Re: Trillium hibbersonii seeds wanted. Post on Scottish Rock Garden Club Forum. October 2, 2009. Website: https://www.srgc.org.uk/forum/ [accessed August 2022].

Wieting, J. 2016. Vancouver Island Old-growth Logging Rate Will Lead to Collapse. Sierra Club BC. https://sierraclub.bc.ca/vancouver-island-old-growth-collapse/

Wiley, L. 1968. Rare Wild Flowers of North America. Wiley, Portland, Oregon. 501 pp.

Zettler, J.A., T.P. Spira, and A.A. Craig. 2001. Yellow Jackets (Vespula spp.) disperse Trillium (spp.) seeds in eastern North America. American Midland Naturalist 146:444-446.

Collections examined

The following collections were examined and/or databases queried for the preparation of this report:

• Canadian Museum of Nature (CAN): No specimens
• Consortium of Pacific Northwest Herbaria Specimen Database (accessed online): Specimens listed under herbarium of origin
• Department of Agriculture, Ottawa (DAO): No specimens available
• Royal British Columbia Museum (V): V176607 (Ceska 1981); V190823 (Roemer 2001); V190824 (Roemer 2001)
• University of British Columbia (UBC): V73131 (Hibberson 1938-holotype); V250698 (Lomer 2019); V250699 (Lomer 2019)

Authorities contacted

• Allen, G. Professor, Biology. University of Victoria. Victoria, British Columbia
• Asencio, S. Collections Manager. National Collection of Vascular Plants (DAO). Ottawa, Ontario
• Batten, R. Botanist. B.C. Conservation Data Centre, Ecosystems Branch, B.C Ministry of Environment and Climate Change Strategy. Victoria, British Columbia
• Blackmun, B. Nootka Area Supervisor. BC Parks, Ministry of Environment and Climate Change Strategy. Campbell River, British Columbia
• de Forest, L. Species Conservation Specialist. Parks Canada Agency. Winnipeg, Manitoba
• Dmitriev, A. Natural Resource Specialist Supervisor. Ministry of Forests. Surrey, British Columbia
• Doubt, J. Curator, Botany. Canadian Museum of Nature. Ottawa, Ontario
• Dunlop, R. Mowachaht/Muchalaht Fisheries Coordinator. Gold River, British Columbia
• Filion, A. Scientific and GIS Project Officer. COSEWIC Science Support, Canadian Wildlife Service, Environment and Climate Change Canada. Gatineau, Quebec
• Govindarajulu, P. Unit Head. Species Conservation Unit, Conservation Science Section, Ecosystems Branch, Ministry of Environment and Climate Change Strategy. Victoria, British Columbia
• Jennings, L. Collections Curator. Beaty Biodiversity Museum, University of British Columbia. Vancouver, British Columbia
• Kroeker, N. Species Conservation Implementation Manager. Parks Canada. Victoria, British Columbia
• Lake, R. Head, Regulatory Affairs. Environment and Climate Change Canada. Nanaimo, British Columbia
• McClaren, E. Conservation Specialist. West Coast Region, BC Parks, Ministry of Environment and Climate Change Strategy. Black Creek, British Columbia
• Miskelly, K. Owner. Satinflower Nursery, Metchosin, British Columbia
• Nielson, J. Director of Lands and Resources. Ka:'yu:'k't'h'/Che:k'tles7et'h' First Nations. Victoria, British Columbia
• Penny, J. Program Botanist. B.C. Conservation Data Centre, Ecosystems Branch, B.C. Ministry of Environment and Climate Change Strategy. Victoria, British Columbia
• Renton, R. Conservation Data and Information Analyst. B.C. Conservation Data Centre, Ecosystems Branch, B.C. Ministry of Environment and Climate Change Strategy. Victoria, British Columbia
• Roemer, H. Botanist. Victoria, British Columbia
• Sadler, K. Head, Species at Risk Recovery. Environment and Climate Change Canada. Nanaimo, British Columbia
• Schnobb, S. Program Support Specialist. COSEWIC Secretariat. Gatineau, Quebec
• Shepherd, P. Species Conservation and Management Ecosystem Scientist III. Parks Canada. Sidney, British Columbia
• Wu, J. Scientific Project Officer. Environment and Climate Change Canada. Gatineau, Quebec

Acknowledgements

Funding for the preparation of this report was provided by Environment and Climate Change Canada.

The status report writers would like to thank Jeff Nielson for providing recommendations on access to fieldwork and Leo Jack and Roger Dunlop for boat transportation. Our gratitude goes to Jenifer Penny (B.C. Conservation Data Centre) for sharing the 2019 survey report; to Justin Dunning, Paul Spriggs, Shane Johnson and Chad Kreutzenstein for sharing their 2022 Clanninick Creek field report; and to Justin, Shane, Chad, and Ian Cruickshank for sharing their 2023 Sydney Inlet field report. Justin and Erica McClaren (BC Parks) generously shared their photographs. Thanks to Alain Filion for preparing the distribution map and calculating EOO and AOO for this report. Much appreciation to Dr. Gerry Allen for reviewing the draft report and clarifying the genetic work that has been done to date on this species and to Kristen Miskelly for providing information on Trillium propagation. Many thanks to Del Meidinger for his assistance in supporting this document through to completion.

Biographical summary of report writer(s)

Carrina Maslovat is a species-at-risk biologist, focused on botany in plant communities at risk. She has a master’s degree from the University of Victoria where she studied native grasses and Garry Oak ecosystem restoration. She has inventoried rare plants in regional, municipal, federal and provincial parks, finding new subpopulations of species at risk and monitoring rare plant populations’ abundance and vitality over time. She has developed management plans for nature reserves, formulated best management practices to minimize impacts to species at risk, and has designed ecological restoration projects to provide habitat for species at risk. She has written six COSEWIC status reports, four status report updates, and several recovery planning documents. She is the owner and lead biologist of Maslovat Consulting.

Ryan Batten is a botanist and plant ecologist with 15 years of experience, specializing in rare plants, wetlands and biodiversity inventories. He brings a broad floristic knowledge from conducting fieldwork in British Columbia, Alberta, Saskatchewan, Ontario and Nunavut. He is an active member of the B.C. Flora Update Committee and has been affiliated with the Royal BC Museum Herbarium for the last decade. In 2019, he prepared the status ranks for all of B.C.’s vascular plants for the federal government’s General Status of Wild Species in Canada program. Ryan frequently works with the B.C. Conservation Data Centre, where he spends the majority of his time drafting conservation status reports, mapping the ranges of rare species and providing training on the NatureServe methodology for status assessment. His current research interests include geospatial floristics, human-mediated dispersal, and traits of rarity.

Appendix 1. Threats assessment for Hibberson's Trillium

Threats assessment worksheet

Species or ecosystem scientific name: Hibberson's Trillium - Trillium hibbersonii

Element ID:

Elcode:

Date (Ctrl + ";" for today's date): 2022-12-02

Assessor(s): Del Meidinger (facilitator), (Co-chair) and Bruce Bennett (Co-chair); Carrina Maslovat (report writer); Jenifer Penny, Brenda Costanzo, Danna Leaman and David Mazzerole (SSC members); and Alyssa Pogson (COSEWIC Secretariat).

References:

Assigned overall threat impact: CD = Medium - Low

Impact adjustment reasons:

Overall, threat comments: Generation time 10 to 20 years; three generations 30 to 60 years; likely more sites exist between southern and northern subpopulations; although about 40% of population in parks now, new sites less likely to be.

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