Wood-poppy (Stylophorum diphyllum) recovery strategy: chapter 3



3.1.1   Description of the species

Stylophorum diphyllum is a perennial herbaceous species up to about 40 cm tall, with a stout rhizome. The leaves are pale beneath and mostly basal, with long stalks.  They are deeply divided, almost to the mid-vein, into five to seven lobed and toothed segments. The flowering stalk has two or sometimes three leaves that are more-or-less opposite about half way up the stem. Stems, sepals, and sometimes leaves have few to many stout, multi-cellular hairs. Flowers are in few-flowered clusters at the end of the flowering stalk.  Flowers have four petals that are 2-5 cm long and bright, rich yellow.  The two sepals are hairy and slightly fleshy. The ovary is densely hairy, more or less elliptical in shape and narrowed to a long style that is persistent in the fruit.  The fruit is a nodding, greyish-green, hairy, slightly fleshy, capsule that splits into three to four segments. All parts of the plant have a yellow to orange, bitter-tasting sap.  A technical description of the species is given in Gleason and Cronquist (1963).

In spring, the large, bright yellow flowers of this species are distinctive.  The leaves are strikingly similar to those of Chelidonium majus (celandine), a common Old World weed.  In Chelidonium the leaves are all alternate in contrast to the basal and opposite or whorled leaves of Stylophorum.  The flowers of Chelidonium are paler and much smaller, with narrow petals about 1cm long, and the sepals and fruit are hairless.

3.1.2      Populations and distributions

Wood-poppy is represented in Canada by only three known populations, near London, Ontario (Figure 1), where it is at the northern limit of its range.  Although it is relatively common in scattered populations at the centre of its distribution in Virginia, Kentucky and southern Illinois, Wood-poppy has always been rare in Canada. All historic populations were from along the Thames River east of London.  It was considered extirpated (Keddy, 1984) until it was rediscovered and reported in 1987 from a woodland along the Thames River in London.   Since then 2 other populations have been found. 

Wood-poppy is ranked S1 in Ontario (NHIC 2005), and all Ontario occurrences probably represent less than 1% of the species’ global population (COSEWIC 2000).

Figure 1: Map of southwestern Ontario showing location of Wood-poppy sites

Figure 1: Map of southwestern Ontario showing location of Wood-poppy sites
The table below summarizes land ownership, population size and habitat notes for all three
Popn. Ownership Number
Date originally discovered Description and notes
A Conservation Authority c. 24 1973 About 5-8 individuals in one clump on a wooded river valley slope, all of which have since died and been replaced by more dispersed recruitment.  Twenty-four plants were counted in 2006.
B Private c.250 1987 Plants in one main patch with scattered outliers in a wooded ravine that was open pasture with clumps of trees in 1946. Contained about 800 individuals in 1993, but was subjected to logging and burial by fill later that year.
C Private c.150 1970’s At the edge of a commercial sugar bush next to a municipal drain.  Rediscovered in 1998. Most plants in a patch with scattered outliers.

3.2    Description of the species’ needs

3.2.1   Ecological role, biological needs and limiting factors

Stylophorum diphyllum is typically a plant of rich deciduous forests, forested ravines and slopes, woodland streams, ravine bottoms and the base of bluffs. Soils generally are somewhat calcareous.  Although wild populations tend to be found under closed canopy forest, garden plants of Stylophorum diphyllum can do well in partial shade or full sun.  The Ontario populations of Stylophorum diphyllum represent the northern limit of its natural range. It appears to be adversely affected in years of cold winters and late springs.

Seeds have an oil-rich elaiosome2 and are dispersed by ants. Ants are attracted to the elaiosome and carry off the seed, but may remove the elaiosome and discard the seed, which then germinates (Gates, 1943, Nordhagen, 1959).  The species of ants involved are unknown.  Seeds have a deep dormancy, but germination rates are high following cold stratification.  There is a high rate of seed predation by mice in Ontario populations.

Seedling establishment is most successful on open or slightly disturbed micro-sites with bare soil.  Plants are capable of flowering in their first year, but usually do not flower in the wild until their second or third year.  Plants have indeterminate flowering that can continue until the fall, but the great majority of flowers are produced over a short period in spring.  Seed set is more successful on early flowers.  The flowers appear to be constructed for insect pollination, but visits by insects are not commonly observed.  Plants are capable of self-pollination.  Once established, plants can survive at least 10 and possibly 20 years or more.  Most adult mortality appears to be due to crown rot.  Late spring frosts can kill plants that have not hardened-off because they have been buried by a snow bank.

Small populations are vulnerable to stochastic events that may cause local extinction, and may suffer inbreeding depression.  One population of Wood-poppy (A) had only a few mature plants, in one small clump.  Although the clump appeared to be about the same size in 1993 that it was in 1973 (Dufton personal communication), several plants have died over the last four or five years.  Since 2004 some new plants have established beyond the main clump.  The largest population (B) lost about 600 plants (80% of the population) in 1993, as a result of fill placement and logging, but now the number of mature individuals appears to be more or less stable.  The third population (C) has not been monitored long enough to determine trends. There is little evidence to date that Wood-poppy in Canada is suffering from inbreeding depression.  Plants out-cross and self-pollinate easily and produce viable and healthy progeny.

Recruitment at Population A has been observed in only one year in 10 years of observation. Seeds at this site are almost all predated by mice (unpublished data).  Seeds collected and planted at the site failed to germinate, although seeds planted under cultivation have germinated and the progeny thrived.  Predation and unknown factors limiting germination appear to be major limiting factors at this site.  No seed removal by ants has been detected at Population A.  It is possible that a suitable ant fauna is missing.

At other sites recruitment of seedlings is sporadic and varies year to year.  Some recruitment does occur, but so far there has not been enough demographic monitoring to determine if it is sufficient to allow the populations to increase.  Spread to nearby sites is generally very low, even though the habitat appears suitable.

Stylophorum diphyllum in Canada is represented by three small populations, separated by several kilometers and at the periphery of the range.  The nearest US populations are several hundred kilometers away, in southwest Michigan. It is unlikely that genetic exchange between the Canadian populations occurs.  Seed dispersal is primarily by ants and is not generally long-distance.  The three sites are too far apart for there to be any possibility of natural rescue effect or re-establishment after a local extinction event. 

3.2.2   Habitat needs

Existing populations of Wood-poppy in Canada are all in mid-aged forest communities dominated by Sugar Maple.  Other associated canopy trees include Bitternut Hickory, American Beech, American Elm, White Ash, Hackberry and Basswood.  Canopy cover ranges from about 65 to 90%.  The most common shrub layer species at Wood-poppy sites include Sugar Maple, Choke Cherry, Alternate-leaved Dogwood, White Ash, Basswood, Wild Red Raspberry, Staghorn Sumac and American Beech.  Shrub cover ranges from more than 75% to less than 5% at different parts of the habitat. All sites have a rich assemblage of woodland ground flora, but it is not identical across sites. 

Nearest neighbours to Wood-poppy plants are most commonly other Wood Poppies.  At Population A the most common associated ground layer species are Garlic Mustard and Jack-in-the-Pulpit.  At Population B and C common associates include Wild Ginger, Virginia Waterleaf, Zig-zag Goldenrod, Blue Cohosh, Wild Geranium and Jack-in-the-Pulpit.  Soils at all sites are mesic glacial deposits that range from sandy loam to clay loam.  Germination sites are often on bare soil that has been disturbed for example by animal activity, falling debris or slumping.  Performance following human disturbances (fill, drainage activities) in and adjacent to the habitat demonstrates that plants can colonize disturbed and/or weedy sites. The species does not normally occupy the entire habitat that is apparently suitable adjacent to where it grows. Limits to Wood-poppy spread are not understood and it is unknown why the species occupies the sites it does and not apparently similar sites in the same area. Under cultivation it grows well in sun or shade and can be quite weedy.

3.3    Threats

The main threats to Wood-poppy populations in Canada have been identified as follows, and are listed in decreasing order of importance: 

3.3.1   Small Population and poor recruitment 

The small isolated populations and poor recruitment rates described above may be limiting the recovery potential of the species and make it more vulnerable to human threats such as recreation, forest management and encroachment from adjacent land use.

3.3.2   Erosion and Fill 

Part of the ravine at Population B was destroyed by filling in 1993.  Additional fill with topsoil and road-building adjacent to the site caused erosion of the ravine in 1997.  At least 5 mature plants have been lost to erosion since then.  Most plants are in less disturbed locations at the site.  A municipal drain runs adjacent to Population C.  Some outlying plants grow in the soil heaps along the drain.  Further drainage operations, would impact these plants.

3.3.3   Change in adjacent Land Use 

Population B is located right at the edge of an Environmentally Sensitive Area within the City of London and has already been affected by activities on and adjacent to the site (see Erosion and Fill).  Current land use adjacent to the site includes agriculture and an industrial plant.  Although the site is outside the current 30-year growth boundary of the City of London Official Plan, new development is taking place on neighboring lots.  It likely that land adjacent to Population B will be zoned for development in the future.  Although The City of London Official Plan and the Provincial Policy Statement provide protection of the site itself, adjacent development would probably increase recreation pressure, and raise the level of disturbance to Population B.

3.3.4   Recreation pressure and trespassing 

Increasing numbers of mountain bikers trespass on the property at two Wood-poppy sites.  At Population A, in a site managed by a Conservation Authority, a combination of signage and moving the trail further from the Wood-poppy population appears to have been effective in reducing the threats.  On the privately owned site at Population B new trails have been formed and marked without the knowledge or consent of the landowner.  The trespassing is very aggressive, including damaged and removed signs, opening closed trails and cutting fences.  Public awareness of the presence of Wood-poppy in London is quite widespread and the location of Population B is quite well known. It is not known how many people have visited the site, or how frequent those visits have been, but the landowners have complained about the numbers of trespassers.   Because the slopes on which the Wood-poppy grows are so steep, they are very vulnerable to damage by trampling.

3.3.5  Forest Management

Logging degraded the habitat of Population B in 1993.  The habitat is regenerating, but some edge trees are still dying.  Shading by understory growth may become a problem. Population C is in a sugar bush.  Management (logging, trails, trampling) could impact the population, but it has apparently survived next to a sugar bush operation for at least 30 years.  The threat at this site does not seem to be imminent.

3.3.6   Invasive species

Garlic Mustard (Alliaria petiolata) is a direct competitor of Wood-poppy at all sites, but especially at Population A.  Garlic Mustard plants immediately adjacent to Wood Poppies are removed each year.  Disturbance from pulling Garlic Mustard here may have created germination sites for Wood-poppy seedlings. Japanese Knotweed (Polygonum cuspidatum) at Population B has been treated to prevent its becoming a problem, but it is not yet eradicated.  Herb Robert (Geranium robertianum) is also of concern at Population B because large numbers of seedlings have been noted under and around mature Wood-poppy plants.  Such plants could be in competition with Wood-poppy seedlings.

3.3.7   Wildflower gardening 

Stylophorum diphyllum is prized by wildflower gardeners and is available for sale as a garden plant.  It can be a prolific, almost weedy, garden plant in southern Ontario, growing well in rich soil in shade or partial sun.  The origin of most garden stock is unknown and is almost certainly not Canadian.  Garden plants have little value for conservation purposes. Extensive cultivation of species of very rare plants is likely to be detrimental to conservation efforts.  Individuals from garden stock may escape into the wild. Adventive plants not only make assessment of natural populations impossible or very difficult, but they may genetically contaminate local stock and may also disrupt the natural community dynamics of the sites where they establish.

3.3.8   Climate 

Stylophorum diphyllum is at the northern limit of its range in Canada and may be temperature limited.  Populations have flourished in the last decade when temperatures have been amongst the warmest on record.  It has been observed that late frosts kill unhardened plants and cool springs adversely affect flowering.  The species may do well under global warming, but other effects of climate change, such as drought and unpredictable conditions may be detrimental.

3.4    Critical Habitat

3.4.1      Identification of the critical habitatof Wood-poppy 

Critical habitat for Wood-poppy is being identified in the Recovery Strategy for all three extant populations, to the extent possible, with further delineation to be completed at the Action plan stage, following the completion of the Schedule of Studies.  Critical habitat includes the current area that the populations occupy plus the surrounding polygon of the same Ecological Land Classification (ELC) vegetation type (Lee et al., 1993). Occasional outliers found away from the main populations indicate that the plants are capable of spreading into adjacent areas within the same polygon.  Critical habitat at Populations B and C should also include adjacent disturbed areas (fill and soil piles) into which there is occasional recruitment.  At Population B where plants grow very close to the edge of the woodland, critical habitat may include portions of the adjacent agricultural land required to protect the habitat from the impending development. 

Critical Habitat applies to the three extant populations and may be updated periodically, as new information becomes available.  

3.4.2      Examples of activities that are likely to result in destruction of the critical habitat 

Examples of activities that are likely to result in the destruction of the critical habitat of wood-poppy include, but are not limited to:

Recreation pressure: Increase in trail creation and use or increased access likely would be detrimental to Wood-poppy and its habitat.

Development: Development adjacent to the Wood-poppy sites would degrade the adjacent natural woodlands and lead to loss of habitat.

Fill, erosion and drainage: Additional filling of the ravine would further damage Wood-poppy habitat. Erosion of existing fill continues and further attempts at fill could damage more habitat.  Road repair or widening adjacent to the ravine could pose further problems.  Drainage operations adjacent to Population C could harm some plants.

Forestmanagement: Heavy logging that opened the canopy or caused damage to the steep-sided ravines would be detrimental.  Any logging would alter the habitat, but changes need not necessarily be detrimental to Woody Poppy populations.   Expansion of sugar bush operations at Population C could harm the Wood Poppies if trees were felled onto the population or the plants were trampled or soil was compacted.

3.4.3   Existing and recommended approaches to habitat protection

Population A is in a Conservation Area and is managed as a natural area.  A trail that was close to the Wood-poppy population has been moved.  The site is monitored so that needs for vegetation management can be recognized and assessed.  Garlic Mustard is pulled annually from the immediate vicinity of the Wood-poppy plants. Shrubs may be thinned if it is appears that Wood-poppy plants are being affected by increasing cover.

Population B is privately owned. The main part of the Wood-poppy population has some protection as a Candidate Environmentally Significant Area  (ESA) under the City of London Official Plan, but the Wood-poppy population extends to the  boundary of the Candidate ESA.  A Comprehensive Community Plan, currently underway, is required to determine the boundary of the ESA and protect the site from future development.  Recreational use is still a current and potential threat.  Development of adjacent lands, currently under active agriculture, is a future threat.  The Recovery Team has assisted the landowner in attempts to control trespassing on the property where it threatens the Wood-poppy population.  The landowner has been informed about options for protection and stewardship of the ESA and adjacent lands.  A proposal to consider acquisition of portions of the land has been submitted to the Thames Talbot Land Trust that already owns another section of the ESA.

Population C is privately owned and lies between an active sugar bush and a municipal drain.  The landowners are aware of the Wood-poppy on site, allow access for monitoring by members of the Recovery Team and have agreed to inform the recovery team if any change in land use is proposed. It may be useful to inform these landowners about options such as easements for the long-term protection of the woodland.  Maintenance or alteration of the municipal drain would likely be detrimental to some Wood-poppy plants that grow on soil piles beside the drain.

3.4.4  Schedule of Studies

Description of Research Activity Start Date Recommended Completion Date
Detailed mapping of Wood-poppy populations onto airphotos using GPS where feasible. 2006 2008
Delineate and describe the nature and extent of the ELC polygons where the plants occur 2006 2008
Conduct habitat mapping 2006 2008

3.5    Actions already completed and underway

Wood-poppy recovery activities were started in 1997 with the formation of a Recovery Team and preparation of a Draft Recovery Plan (Bowles, 1997).  Recovery actions completed or ongoing include the following:

a)     Search for additional Wood-poppy sites.  One additional site that was known from the 1970’s, but not reported in the literature or supported by collections was rediscovered.  The number of mature individuals known increased to about 400 in three sites.

b)     Landowner contact and landowner involvement with the Recovery Team.

c)     Mapping of significant habitat by MNR for application of the Conservation Land Tax Incentive Program (CLTIP) and the Provincial Policy Statement (PPS) at two of the three sites.

d)     Regular monitoring of the existing populations.  Increased knowledge of survival, recruitment and fecundity for population viability analysis.

e)     Habitat protection and management at the two sites where control of public access, trail closure, signage, invasive plant control are needed. Some trail closures have been successful, but a systemic problem of trespassing exists at one site.  Invasive species control and control of public access will continue.

f)       Establishment of ex-situ populations of Wood-poppy at the Environmental Sciences Field Station at University of Western Ontario and the Royal Botanical Gardens. About 200 mature plants of 21 maternal lines survive at the two locations.  Populations will be maintained for study. Additional small ex situ populations are established at Thorndale and South Walsingham, Ontario from seed collected in 1993.

g)     Germination and seed dispersal experiments have been done.  These have helped determine causes of low recruitment rates.  Seed:ovule ratio is moderate, fecundity is high, germination rates are high, but seed survival in the wild is poor.  Many seeds (up to 100%) are predated after release from the capsule (Bowles, unpublished data).  Dispersal by ants does not appear to be taking place at the site with the smallest population, Population A (Bowles, unpublished data).

h)     Seed storage experiments have been done for Canadian populations.  Stored seeds (2-3 years) failed to germinate (personal observation).  Long-term viability of stored seeds may be poor. Viability of seeds in the main part of the range is unknown.

i)       Fifty seeds from Population A were planted in the fall of 2004, but failed to germinate.  Additional seeds will be planted in the fall of 2005, for germination in the spring of 2006.  Juvenile and young mature plants, if seeds germinate, will be planted into the wild in fall 2006.

j)       Material for genetic analysis has been collected from Canadian and US populations of Wood-poppy.  Search for primers for genetic analysis is underway.  The MNR forensic lab at Trent University is undertaking the work, but lack of funds precludes hiring a full time technician.

k)     Articles about Wood-poppy and the recovery actions have been published in naturalist magazines and regional media to raise awareness.

2 Elaiosome: structure on surface of some seeds that contains an oily substance that aids in seed dispersal by attracting certain organisms such as ants

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