Muhlenberg's centaury (Centaurium muehlenbergii COSEWIC assessment and status report: chapter 2

COSEWIC Executive Summary

Muhlenberg’s centaury
Centaurium muehlenbergii

Species information

Muhlenberg's centaury (Centaurium muehlenbergii) is a small annual herb in the gentian family. It has opposite leaves and pink or white tubular flowers with flaring lobes, and typically grows to 4-8 cm in its Canadian habitat.

Distribution

The range of the species extends from British Columbia south to Oregon, Idaho, Nevada and California. Only three extant populations are known in Canada, all on or near southeastern Vancouver Island. There is a single population in Greater Victoria, one on the Gulf Islands, and one near Nanaimo. The species’ Extent of Occurrence is 160 km² and its Area of Occupancy is <20 km². The actual total area of habitat occupied, however, is only about 110 .

Habitat

Muhlenberg's centaury is found in the Coastal Douglas-Fir Biogeoclimatic Zone, where it occurs in habitats ranging from vernal pools (water only present in the spring) and seeps to the margins of a coastal salt marsh. Increasing urbanization around Victoria, combined with the draining of wetlands for agricultural uses and development, has altered the ecology of the region to such an extent that the amount of area suitable for supporting this species is now significantly reduced compared with historical levels.

Biology

Muhlenberg's centaury is an annual species; it flowers in the summer and produces several small seeds that remain dormant through the winter and germinate the following year. Some seeds probably remain dormant for longer than a year, forming a persistent seedbank, but this has not been confirmed. Little else is known about the ecology of this species, including its germination requirements, survival and recruitment rates, dispersal mechanisms, and intrinsic vulnerabilities to disturbance.

Population sizes and trends

Total population size at the three extant sites is currently estimated to be between 500 and 1000 individuals. The majority of these occur at a single site. There is no evidence of population declines in the last 10 years, and populations appear to be more or less stable.

Limiting factors and threats

The ecological factors naturally limiting the abundance and distribution of this species are largely unknown. Aside from habitat loss due to urbanization, the primary threats to its persistence in Canada are: competition from introduced species, especially grasses; trampling by people, dogs, and bicycles; off-road vehicle traffic; hydrologic alterations; altered fire regimes; and disturbance from Canada geese.

Special significance of the species

Species in the genus Centaurium have long been held in regard for their medicinal properties, although Muhlenberg's centaury is not known to have any such uses in Canada.

Muhlenberg's centaury may be of special interest genetically, insofar as peripheral populations are often genetically distinct from those in the core of the range.The British Columbia population of Muhlenberg centaury is about 300 km disjunct from the northern extent of its main range in California and Oregon.

Existing protection or other status designations

Muhlenberg's centaury is Red-listed in British Columbia; it has a provincial conservation rank of S1 (critically imperilled) and a national heritage rank of N1. However, there is no legal protection in place either for it or its critical habitat in Canada. The species can be added to the list of species under the B.C. Wildlife Amendment Act (2004) by provincial cabinet if the species is listed as extirpated, endangered or threatened in B.C. on the basis of a detailed status assessment.

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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 (2008)

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 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 Canada, provides full administrative and financial support to the COSEWIC Secretariat.

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