White wood aster (Eurybia divaricata) COSEWIC assessment and status report: chapter 2

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Executive Summary

Species information 

Eurybia divaricata is a fall-flowering herbaceous perennial. Deeply serrated upper leaves and narrowly heart-shaped lower leaves characterize this species. Flat-topped clusters of small flower heads also distinguish it. The flower heads are yellow and purple in the center with white rays.

Distribution 

Eurybia divaricata occurs in Canada and the United States.  This species is generally common throughout its main range in the Appalachian Mountains, and from New England south to Georgia and Alabama. In Canada, Eurybia divaricata occurs in scattered populations in the Niagara Region of southern Ontario and in a few woodlots in southwestern Quebec. 

Habitat

This species inhabits dry to moist deciduous woodlands with well-drained soils and relatively open canopies.

Biology

Flowering occurs in early August to September.  Fruiting occurs in mid to late September.  This species spreads clonally through rhizomes.

Population sizes and trends

In Canada there has been an increase in the reported number of populations since 1995.  Number of reported locations and population sizes (number of stems) within the populations in Ontario have increased.  Populations in Quebec have not been monitored consistently, but it appears that although the number of reported locations has increased, the number of viable populations is low and may be decreasing.

Limiting factors and threats

The major threats to this species are habitat loss, grazing by deer and consumption by weevils, tramping and possibly invasive species.

Special significance of the species

This species is one of the least common in the Asteraceae and is at the northern edge of its range in Ontario and Quebec.  

Summary of status report

There are only 25 reported locations of Eurybia divaricata in Canada, 15 in Ontario and 10 in Quebec, many of which have not been monitored for several years.  Fewer than 10,000 plants have been documented. Of the populations that have been confirmed recently, all but two are threatened to some degree, either by habitat destruction and development, trampling, small population size or environmental factors such as competition with invasive species and deer browsing or weevil consumption.  Many of the sites in Ontario are located on public lands and do have some protection through management, but the majority of Quebec populations are on private lands where they are at risk.

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 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.

 

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)*

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

Not at Risk (NAR)**

A species that has been evaluated and found to be not at risk.

Data Deficient (DD)***

A species for which there is insufficient scientific information to support status designation.

 

 

*

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.

 

 

 

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.