Willowleaf aster (Symphyotrichum praealtum) COSEWIC status assessment and status report chapter 2

Executive Summary

Willowleaf Aster
Symphyotrichum praealtum

Species Information

Willowleaf aster is an herbaceous, rhizomatous, upright perennial with a relatively smooth and waxy stem growing to 1.5 m tall. The upper stem leaves are generally narrow, linear, with a few small teeth along the margins and lack leaf stalks; the lowermost leaves have usually shriveled and fallen off at the time of flowering. The inflorescence consists of a series of leafy flower clusters with the lowermost branches generally being the longest. The stalks of the flowering heads are moderately to densely hairy. The hairless, leaf-like bracts (phyllaries) surrounding the flower heads are borne in 4-6 strongly graduated series; each has a small, green, diamond-shaped zone towards the tip. The flower heads have 20-35 outer florets with pale blue-violet rays; the central yellow disc florets number 20-30 and become purple with age.

Distribution

Southwestern Ontario is the northeastern range limit of this species. It is found in Lambton, Essex and Middlesex Counties and the Municipality of Chatham-Kent.

Habitat

Over its total range, this aster is found in thickets, meadows and prairies, as well as in oak savannahs as found in the Windsor area and on Walpole Island.

Biology

Throughout its range in North America, the species comprises several varieties with varying numbers of chromosomes. The entity that is present in Ontario (var. praealtum) has double the normal set of chromosomes (2n = 32). Like other asters, var. praealtum is a facultative out-breeder. Self-fertilization is possible but typically occurs only at a low level. Thus, large colonies consisting of a single clone will only set a few seeds even though thousands of heads may have been in bloom during the season. This has a significant consequence for the long-term adaptability of the species in sites consisting of single clone populations.

Population Sizes and Trends

About 12 extant populations are known. The species is clonal and actual numbers of individuals are difficult to determine, but clone sizes range from one shoot to over 100 shoots. Three populations are known only from reports in the 1960s. At least one population has been extirpated. No trend information is available.

Limiting Factors and Threats

Most populations consist of scattered clones at the edge of woods, in woodland openings or along the banks of streams and ditches. Habitat loss due to construction or agriculture is the main threat to this species in Canada.

Special Significance of the Species

The species has no known unique economic or biological significance. In part, perhaps, due to its similarity to another more widespread aster of southern Ontario, no specific Aboriginal use has been found in the literature.

Existing Protection or Other Status Designations

A number of clonal populations occur in Ojibway Nature Center, Ojibway Prairie Provincial Nature Reserves and Tall-grass Heritage Park in the City of Windsor; these are protected. Other populations are on private property with no formal protection at all.

Summary of Status Report

Willowleaf aster is a highly localized species occurring in southwestern Ontario mainly in two areas of concentration around Windsor and Walpole Island. About 13 localities are known for this clonal species with perhaps a total of several thousand flowering stems. Risks to the species are posed by the nearness of some of its clones to roadsides and agricultural areas with potential impact from human activities.

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)Footnote1
A species of special concern because of characteristics that make it particularly sensitive to human activities or natural events.

Not at Risk (NAR)Footnote2
A species that has been evaluated and found to be not at risk.

Data Deficient (DD)Footnote3
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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