Dwarf woolly-heads, specific populations, COSEWIC assessment status report: chapter 2

• Previous page
• Table of contents
• Next page

COSEWIC Executive Summary

Species information

Dwarf woolly-heads (Psilocarphus brevissimus) is a low, woolly annual herb with short, opposite leaves. The heads lack whorls of bracts that form an involucre that surrounds the heads of most members of the aster family; they also lack rays or any showy structures and are copiously woolly and inconspicuous like the rest of the plant. Each head is lobed and each lobe contains a few central male flowers surrounded by anywhere between 8 and 80 female flowers. The female flowers are each partially enclosed by a minute, woolly, sack-like receptacular bract that has a lateral, translucent appendage. The style, near the tip of the achene, is offset.

Distribution

In Canada, Psilocarphus brevissimus occurs in south central British Columbia and in southeast Alberta/southwest Saskatchewan. The two groups of populations, referred to as the Southern Mountain Population and Prairie Population respectively, appear to function as separate evolutionary units because they are not united by a continuous distribution of populations to the south. The species’ global range extends through central and eastern Oregon south along both sides of the Sierra Nevada Mountains to Baja California as well as in Argentina and Chile.

Habitat

Psilocarphus brevissimus occurs in vernal pools, temporarily flooded depressions and drawdown areas along lakes and ponds. Some of the potential habitat has been lost over the past century due to agricultural development and invasion by exotic grasses and shrubs. The amount of suitable habitat fluctuates greatly depending on the degree of spring flooding.

Biology

Psilocarphus brevissimus is an annual that flowers and fruits in mid- to late summer. Its floral structure is strongly adapted to favour self-pollination. The seeds are dispersed in the late fall. The seeds are enveloped by a woolly receptacular bract and lack structures to aid long-distance dispersal. The seeds germinate during the early summer but the plant continues to develop even as the surrounding uplands become droughty. The ability to tolerate high moisture levels in the winter and very low moisture levels in the summer allows it to grow where many other plants would succumb to environmental stress.

Population sizes and trends

Populations fluctuate greatly among years, depending on rainfall and flooding. The Southern Mountain Population may have as few as 700 mature individuals in ‘trough’ years and perhaps as many as 2,000,000 in ‘peak’ years. The Prairie Population may have as many as 27,000 individuals in ‘peak’ years but many sub-populations disappear completely during trough years, when the aggregate population may be as low as 2,000 individuals.

Limiting factors and threats

The Southern Mountain Population is highly susceptible to extirpation because there are very few localities and they are restricted to small areas of suitable habitat. The primary threats to this population in Canada come from habitat alteration due to changes in hydrology and grazing practices. Other threats include the use of herbicides to control invasive species on the surrounding rangelands and all-terrain vehicle use.

The Prairie Population is threatened by agricultural development, oil and gas exploration, range management practices and weed control measures.

Special significance of the species

The Canadian populations may be remnants of a broader distribution during the warm, dry Hypsithermal Interval.

Existing protection or other status designations

Dwarf Woolly-heads (Psilocarphus brevissimus) was first assessed by COSEWIC as Endangered in Canada in 2003. However, because the original status report failed to note the presence of the Prairie Population, which is present at numerous sites in southeastern Alberta and southwestern Saskatchewan, COSEWIC requested that a new update report be prepared for re-evaluation of the species' conservation status. Psilocarphus brevissimus has no species-specific protection in Canada or elsewhere. Only 2 of the 41 Prairie Population sites are known to occur in protected areas and all three of the Southern Mountain Population sites occur on private land.

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^th 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 (2006)

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)^Footnotea

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)^Footnoteb

A wildlife species that has been evaluated and found to be not at risk of extinction given the current circumstances.

Data Deficient (DD)^Footnotec

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.