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Astragalus microcystis Gray

Least Bladdery Milkvetch

Fabaceae (Pea family)

General Description: Tap-rooted perennial with numerous spreading or ascending stems 10-50 cm long and purplish at the base. The compound leaves have 9-15 elliptic to oblanceolate leaflets, 5-15 mm in size. The stems commonly have appressed hairs. The leaves have a more loose pubescence. Racemes are loosely 5-12 flowered. Flowers are 6-9 mm long, early declining, and pink or pale lavender to magenta-purple in color. The calyx is densely pubescent with whitish to blackish appressed hairs. Pods are sessile, bladdery inflated, 5-12 mm long, and have short white and sometimes a few black hairs.

Illustration.

Field Identification Tips: The loosely tufted or trailing habit, relatively small flowers, and the small, swollen fruits often broadest a little above the middle help distinguish this species from other Astragali. Plants from lower elevations and from lake shores tend to have longer stems, wider leaflets, more numerous flowers and larger pods than those from stony habitats in the mountains.

Phenology: Flowers late April to August.

Similar Species: Related to A. vexilliflexus which can look quite similar. However, this species does not occur in northern Idaho.

Habitat: Rangewide it is known from rocky and grassy hillsides, gravelly flats, open woods, and sandy or stony lake and river shores.

Global Distribution: Southern British Columbia, western Montana, northern Idaho, and northeastern Washington. It is also disjunct in the eastern Olympic Mountains in western Washington.

Idaho Distribution: The handful of Idaho collections are all from around Lake Pend Oreille in Bonner and northern Kootenai counties. This species has not been collected in Idaho since 1958, and most if not all of these earlier collections may have been taken from lake shore areas. This is habitat that has been lost or altered due to frequent dam-induced fluctuations in the lake's water level.

References:

Barneby, R. C. 1964. Atlas of North American Astragalus. Memoirs of the New York Botanical Garden Vol. 13. The New York Botanical Garden, Bronx, NY. 1188 pp.

Straley, G. B., R. L. Taylor, and G. W. Douglas. 1985. The rare vascular plants of British Columbia. Syllogeus No. 59. National Museum of Natural Sciences, National Museums of Canada, Ottawa, Canada. 165 pp.

Washington Natural Heritage Program. 1999. Field guide to Washington's Rare Plants. Cooperative Challenge Cost-share Project, Spokane District, USDI Bureau of Land Management and Washington Natural Heritage Program, Washington State Department of Natural Resources.