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Recovery Strategy for the Contorted-pod Evening-primrose (Camissonia contorta) in Canada

1. COSEWIC Species Assessment Information

Date of Assessment: April 2006

Common Name (population): Contorted-pod Evening-primrose

Scientific Name: Camissonia contorta

COSEWIC Status: Endangered

Reason for Designation: An annual herb restricted to several dry, open and sandy coastal habitats of very small size. The small fragmented populations are impacted by ongoing habitat loss, high recreational use and competition with several invasive exotic plants.

Canadian Occurrence: British Columbia

COSEWIC Status History: Designated Endangered in April 2006.

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2. Species Status Information

Contorted-pod Evening-primrose is ranked globally secure (G5; NatureServe 1988), but critically imperiled in Canada (N1; NatureServe 1988) and in British Columbia (S1; B.C. Conservation Data Centre 2011). Its status in Washington, Oregon, California, Nevada and Idaho has not been ranked (NatureServe 1988). It was ranked critically-imperiled in Vermont but this was based on a misidentification and should be rejected as the species does not occur in that jurisdiction (NatureServe 1988). There is no estimate of global abundance, but the Province of British Columbia considers the species to have less than 10% of its global abundance in the province (B.C. Conservation Framework 2010).

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3. Species Information

3.1 Species Description

Contorted-pod Evening-primrose (Figure 1) is a slender, annual herb, occasionally growing to 40 cm long, arising from a slender taproot. Its stem is wiry, usually branched, peeling below and often sprawling. Its leaves are linear to narrowly elliptic, 5-30 mm long and entirely to remotely toothed. The flowers are borne on a short stalk or are unstalked. Each flower consists of four sepals and four petals. The petals are 3-5 mm long and yellow, fading to red. The stems, leaves and capsules are often deep red, particularly in unshaded environments.

Figure 1. Illustration of Contorted-pod Evening-primrose (from Vascular Plants of the Pacific Northwest, by L.C. Hitchcock, A. Cronquist and M. Ownbey, with illustration by J.R. Janish), published by the University of Washington Press (1969); and photo by Matt Fairbarns. Both images used with permission.

Illustration and photo of Contorted-pod Evening-primrose
© Illustration - University of Washington Press (1969); and photo - Matt Fairbarns

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3.2 Population and Distribution

Contorted-pod Evening-primrose ranges from British Columbia (B.C.) to California, east to Idaho and western Nevada (see COSEWIC 2006 for additional details). In Canada, it is at the northern edge of its global range (Natureserve 1988).

In Canada, populations of Contorted-pod Evening-primrose occur in an approximately 750 km2 extent of occurrence near the coast on southeast Vancouver Island and the Gulf Islands of B.C. (Figure 2). There are records of nine populations in Canada (Figure 2, Table 1), one of which has been extirpated (Population 9 was last observed in 1893). Due to loss and degradation of sandy habitats on the coast of B.C., the historical number of populations might have been higher than nine. Thirty sites with sandy habitats that appear suitable for this species were surveyed between 2004 and 2006 to confirm that no undetected populations were present in the region (COSEWIC 2006).

Figure 2. Distribution of Contorted-pod Evening-primrose in Canada (from COSEWIC 2006). Extant populations are shown by solid stars and the one extirpated population is shown by a solid square. Due to the scale used for this map, Northern Gulf Island Populations 3 and 4 are shown as a single symbol. The open star shows location of nearest U.S. population.

Distribution of Contorted-pod Evening-primrose in Canada
© Matt Fairbarns

In the status report (COSEWIC 2006), the Canadian population was estimated at 3,500 – 4,500 individuals with an area of occupancy of 7.84 ha (surveys conducted in 2004). In 2005, Population 7 expanded slightly into areas unoccupied in 2004 and increased in abundance. Surveys in 2006 (after the last status assessment by COSEWIC) revealed that all plants at Population 6 had been destroyed during a land development project, but in 2007 a small number of plants were observed in or near the original location (Table 1). The exact location of these plants is not known, and it is not clear if they were in the same location as the extirpated population or at a different location nearby. Similarly, as described in COSEWIC (2006) Population 8 was destroyed by off road vehicle use, but that threat has been at least partially mitigated through the use of barriers and the population has since naturally re-colonized the site (Table 1).

Revising population totals since the field work was completed for the COSEWIC assessment, the total Canadian population was estimated to have declined overall from 2004 to 2006 to about 2,250-2,850 individuals (due primarily to destruction at one site), occupying about 38.1 ha. This constitutes an estimated decline in total population size of approximately 36% (following COSEWIC standard of using the lowest population numbers when provided with a range of values), with a possible range from 19-50%. The reason why the area of occupancy has risen while population numbers have fallen is because a small number of new plants have been discovered over a relatively large area, so this small discovery of individuals has greatly expanded the known area of occupancy. Thus, area of occupancy is currently a poor measure of overall population trend for this species.

Table 1. Summary of Populations of Contorted-pod Evening-primrose in Canada.
Population number and name[1]StatusRecent recordsLand Tenure
Last year observedLast population census (year)
1. MetchosinExtant2006253 (2004)Capital Regional District Park
2. Saanich AExtant2006500-1,000 (2004)Capital Regional District Park
3. Savary Island AExtant2006190 (2004)B.C. Ministry of Transportation and Infrastructure
4. Savary Island BExtant2004700 (2010)Private
5. Saanich BExtant2006500-600 (2004)Private (James Island)
6. Saanich CExtant2007100 (2007)Private (James Island)
7. Saanich DExtant2005114 (2005)Gulf Islands National Park Reserve and Canadian Coast Guard
8. Saanich EExtant2007200-250 (2007)Cordova Spit Municipal Park
9. Cedar HillExtirpated18930 (2005)Exact location unknown

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3.3 Needs of the Contorted-pod Evening-primrose

For a detailed description of the biology of the species, see COSEWIC (2006). Contorted-pod Evening-primrose does not reproduce asexually (i.e., from cuttings or pieces of the plant). Thus, reproduction and dispersal of the species is dependent on seeds. It is an annual species so populations are replenished either by recruitment from a local seed bank and/or by dispersal from other populations. It is not known if Contorted-pod Evening-primrose is capable of banking dormant seeds in the substrate for two or more years and there are no studies on its population processes that might advise on its ability to bank seeds. Dispersal between populations is probably an uncommon event.

In Canada, Contorted-pod Evening-primrose inhabits sandy backshore[1] habitats in the Southern Gulf Islands and Strait of Georgia Ecosections, where it occurs in the Coastal Douglas-fir Biogeoclimatic Zone (B.C. Ministry of Environment n.d., B.C. Ministry of Forests 2003). Key site characteristics are listed in Table 2.

Table 2. Key habitat attributes of sites where Contorted-pod Evening-primrose is found in Canada.
Elevation (m)0-20
Aspect (degrees)Various, usually 145-270 if slope > 5%
Slope Angle (%)0-50
Meso-slope PositionLower slope or level
ExposureModerately exposed to wind and salt spray
DrainageVery rapidly
Mineral Soil TextureSandy
Surface Organic Horizon< 0.5 cm
Root-restricting LayerNone
Coarse Fragments< 1%
Terrainsandy aeolian blanket or thick veneer

Contorted-pod Evening-primrose appears to tolerate light levels of sand erosion and deposition and may require such disturbances in order to escape competition (Fairbarns, pers. obs.). In Canada, it is absent from more active areas of sand dunes and other sites with unvegetated sand. In the nearby San Juan Islands of Washington State, however, it sometimes occurs in slightly more active dune blow-outs, where individual plants may develop a spreading patch up to one metre in diameter.

Contorted-pod Evening-primrose is restricted to sites that have negligible tree or shrub cover, although the non-native and invasive Scotch Broom (Cytisus scoparius) sometimes grows nearby. Herbs, mosses and lichens tend to be sparse. The cover of herbaceous plants usually varies from 1-20% but may be as high as 50%. Native herbaceous species such as Tall Pepper-grass (Lepidium virginicum), Native Red Fescue (Festuca rubra), Sea-blush (Plectritis congesta) and Blue-eyed Mary (Collinsia parviflora) are often present. Contorted-pod Evening-primrose often grows with mosses (primarily Roadside Rock Moss, Racomitrium canescens, and Awned Haircap Moss, Polytrichum piliferum) but it is usually absent from microsites where the moss cover exceeds 30%.

Demographic collapse constitutes a probable, moderate and ongoing issue because all populations of Contorted-pod Evening-primrose are threatened simply by their small size. Annual species, such as Contorted-pod Evening-primrose, that do not produce offshoots and which survive because they can tolerate levels of stress too high for most species tend to be particularly prone to extirpation and thus have comparatively high Minimum Viable Population (MVP) sizes (Pavlik 1996, Traill et al. 2007). Pavlik (1996) reviewed three studies and reported that a reasonable working definition of MVP size for plant reintroduction projects would range from about 50–2500 individuals, depending on the life history of the species in question. Based on a review of 22 papers, Traill et al. (2007) reports for plants (annual and perennial) a median MVP size of about 4,824 individuals. For Contorted-pod Evening-primrose, several life history traits would predispose it to having a relatively large MVP compared to most plants (e.g., annual, herbaceous, occurring in habitat with high environmental variation, etc), so MVP likely will fall at the higher end of the range for plants (i.e., towards 5,000 individuals). The specific MVP size for Contorted-pod Evening-primrose has not been determined, but determining it is a recommended action for research (see Table 4).

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1 Defined as the coastal zone lying between the beach berm and the backshore slope, affected by waves only during severe storms.