Species Profile

Slender Mouse-ear-cress

Scientific Name: Halimolobos virgata
Taxonomy Group: Vascular Plants
COSEWIC Range: Alberta, Saskatchewan
COSEWIC Assessment Date and Status Change: May 2000
COSEWIC Status: Threatened
COSEWIC Status Criteria: D2
COSEWIC Reason for Designation: A biennial species known from fewer than ten sites in very localized areas of southeastern Alberta and southwestern Saskatchewan. There its populations vary considerably in size, from place to place, and yearly, depending on rainfall.
COSEWIC History of Status Designation: Designated Endangered in April 1992. Status re-examined and designated Threatened in May 2000.
SARA Status: Schedule 1, Threatened
Date of Listing (yyyy-mm-dd): 2003-06-05

Please note that this information is provided for general information purposes only. For the most up to date and accurate list of species listed under the Species at Risk Act, please see the Justice Laws Website.

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Quick Links: | Photo | Description | Distribution and Population | Habitat | Biology | Threats | Protection | Recovery Initiatives | Recovery Team | National Recovery Program | Documents

Image of Slender Mouse-ear-cress

Slender Mouse-ear-cress Photo 1



The Slender Mouse-ear-cress is a biennial plant that grows from 10 to 35 cm high. It can have one or several simple or branched greyish stems that are covered with hairs. Leaves form a basal rosette (dense, radiating cluster of leaves) and also occur along the stems, each of which ends in several flowers. Each flower has 4-mm white petals with prominent pink or lavender veins and six stamens. The elongated, flattened seed capsules contain many seeds.


Distribution and Population

The Slender Mouse-ear-cress is endemic to (found only in) western North America from southern California east to Utah and north to southern Canada. In Canada, it occurs at the northern limit of its range in disjunct populations restricted to a very small area in southeastern Alberta and southwestern Saskatchewan. It is known to have occurred at five sites in Alberta, but now exists at only three of these, and the population numbers have decreased form a total of about 1000 plants in 1997 to several hundred individuals in 1999. In Saskatchewan, the species has been extirpated from one site, and a few plants occur at another. Because the Canadian population size can fluctuate dramatically, reliable population estimates are unavailable and the long-term population trend is unknown.



The Slender Mouse-ear-cress grows in open, short- to mid-grass prairie in sandy, alkaline soil that is dry for most of the year but may be moist in spring. It grows on flat areas or in low prairie depressions, but is inexplicably absent from great stretches of similar suitable habitat.



Very little is known about the general biology of the Slender Mouse-ear-cress. It may flower in its first year, but usually is an ephemeral biennial that is subject to large and inexplicable population shifts from year to year. It may occur in the hundreds, but usually grows as several to a couple of dozen plants in small patches within a wide expanse of suitable habitat. It may be short and single-stemmed one year and robust, tall and well-branched the next. The factors responsible for these variations are largely unknown.



The species is at the northern edge of its range where it is limited by climate. The main threat to the Canadian populations of Slender Mouse-ear-cress is loss of habitat as a result of urban and industrial development and agriculture. It appears to be unable to grow on previously turned soil. Other limiting factors include invasion of its habitat by non-native species and trampling by ATVs and other human activities (e.g., campgrounds).



Federal Protection

The Slender Mouse-ear-cress is protected under the federal Species at Risk Act (SARA). More information about SARA, including how it protects individual species, is available in the Species at Risk Act: A Guide.

The Slender Mouse-ear-cress occurs within Suffield National Wildlife Area which is federal land protected under SARA. It is also protected by the Saskatchewan Wildlife Act. Under this Act, it is prohibited to kill, harass, or harm this species.

Provincial and Territorial Protection

To know if this species is protected by provincial or territorial laws, consult the provinces' and territories' websites.


Recovery Initiatives

Status of Recovery Planning

Recovery Strategies :

Name Recovery Strategy for the Slender Mouse-ear-cress (Halimolobos virgata) in Canada
Status Final posting on SAR registry


Recovery Team

Prairie Plant Species at Risk Recovery Team

  • Candace Neufeld - Chair/Contact - Environment Canada
    Phone: 306-975-4101  Send Email



PLEASE NOTE: Not all COSEWIC reports are currently available on the SARA Public Registry. Most of the reports not yet available are status reports for species assessed by COSEWIC prior to May 2002. Other COSEWIC reports not yet available may include those species assessed as Extinct, Data Deficient or Not at Risk. In the meantime, they are available on request from the COSEWIC Secretariat.

4 record(s) found.

Recovery Strategies

  • Recovery Strategy for the Slender Mouse-ear-cress (Halimolobos virgata) in Canada (2012-11-30)

    The Species at Risk Act (SARA, Section 37) requires the competent minister to prepare recovery strategies for listed extirpated, endangered or threatened species. Slender Mouse-ear-cress was listed as Threatened under SARA in June 2003. Environment Canada led the development of this recovery strategy. This recovery strategy was developed in cooperation or consultation with provincial jurisdictions in which the species occurs – Saskatchewan, Alberta; industry stakeholders, the Department of National Defence and Agriculture and Agri-Food Canada.

Permits and Related Agreements

Residence Description

Critical Habitat Descriptions in the Canada Gazette

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