Scouler's catchfly (Silene scouleri ssp. grandis): COSEWIC assessment and status report: chapter 2

COSEWIC Executive Summary

Coastal Scouler’s Catchfly
Silene scouleri ssp.grandis

Species Information

Silene scouleri ssp. grandis (coastal Scouler’s catchfly) is an erect, perennial forb growing in clumps from a taproot and a generally branched caudex. The plants have a rosette of basal leaves and paired opposite leaves on the stem. The leaves are hairy, entire and unstalked above. The inflorescence is a narrow spike of greenish-white to purple flowers. The calyx is prominently nerved and the petals have two lobes and two appendages. The fruit is a capsule containing numerous pimply seeds. This plant is distinct from other species within its habitat, even in vegetative form.

Distribution

In Canada, Silene scouleri ssp. grandis occurs on three small islands close to Victoria, British Columbia. Globally, it occurs along the Pacific coast from British Columbia to San Francisco Bay.

Habitat

Silene scouleri ssp. grandis occurs in grass-forb meadows close to sea level. It Is shade-intolerant and occurs on soils that are at or near saturation throughout the winter but become very dry during the summer. It was formerly known from one higher elevation site (over 200 m) but that population had low vigour and appears to have disappeared as a result of natural causes.

Biology

Little research has been done on Silene scouleri, even at the species level. Silene scouleri ssp. grandis probably germinates in the spring when soil moisture and temperature conditions are most favourable. In Canada, spring and summer growth is slow and flowering does not occur until late summer or early autumn. Flowers are probably protandrous (anthers develop and wither before styles elongate) and most pollination is probably effected by insects, although plants may be capable of limited selfing.

Population Sizes and Trends

At least seven populations have disappeared since 1897. Trends in the two remaining populations are uncertain because of the lack of data. The Trial Island sub-population is very small (5 individuals) and careful searches in 2000, 2001 and 2002 did not reveal any young plants. The nearby sub-population on Little Trial Island consists of 23 mature plants. The Alpha Islet population is larger (250-300 plants) and was not surveyed for evidence of young plants.

Limiting Factors and Threats

Populations have been lost through habitat destruction but the primary threats to the two remaining populations are habitat degradation due to invasion by exotic shrubs and grasses, altered fire regimes, trampling and marine pollution. Weak reproductive effort and limited powers of seed dispersal impede recovery of depleted populations.

Special Significance of the Species

Populations of Silene scouleri ssp. grandis are at the northern limit of its range and may represent a genetically distinct element important for the long-term survival of the species. Silene scouleri is an attractive garden plant commercially available from numerous sources. Essences of Silene scouleri are commercially available.

Existing Protection

There is no general protection for Silene scouleri ssp. grandis at the provincial or federal level. Both of the populations lie at least partly within ecological reserves where they are legally protected from collecting. Neither population is protected from trampling, competition from exotic weeds, ingrowth by native shrubs or marine oil pollution.

Summary of Status Report

Silene scouleri ssp. grandis occurs in Canada only on three small islands offshore of Victoria, British Columbia. The extent of occurrence is only 0.6 km² and the area of occupancy is only 0.0158 km² (1.58 ha). This distribution is severely fragmented and there is negligible opportunity for genetic interchange between the two populations.  There is little remaining suitable habitat and the quality of occupied and potential habitat continues to decline as introduced grasses and shrubs continue to invade suitable sites. Occupied sites are subject to trampling, mowing and occasional herbicide use. Both populations are at risk from marine oil pollution.

There are fewer than 350 plants in Canada. There is negligible opportunity for unassisted colonization of unoccupied sites due to natural limitations on seed production and dispersal.

COSEWIC Mandate

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) determines the national status of wild species, subspecies, varieties, and nationally significant populations that are considered to be at risk in Canada. Designations are made on all native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fish, lepidopterans, molluscs, vascular plants, lichens, and mosses.

COSEWIC Membership

COSEWIC comprises representatives from each provincial and territorial government wildlife agency, four federal agencies (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biosystematic Partnership), three nonjurisdictional members and the co-chairs of the species specialist groups. The committee meets to consider status reports on candidate species.

Definitions

Species
Any indigenous species, subspecies, variety, or geographically defined population of wild fauna and flora.

Extinct (X)
A species that no longer exists.

Extirpated (XT)
A species no longer existing in the wild in Canada, but occurring elsewhere.

Endangered (E)
A species facing imminent extirpation or extinction.

Threatened (T)
A species likely to become endangered if limiting factors are not reversed.

Special Concern (SC)Footnotea
A species of special concern because of characteristics that make it particularly sensitive to human activities or natural events.

Not at Risk (NAR)Footnoteb
A species that has been evaluated and found to be not at risk.

Data Deficient (DD)Footnotec
A species for which there is insufficient scientific information to support status designation.

 

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.

 

Canadian Wildlife Service

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

 

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