E-Flora BC: Electronic Atlas of the Flora of British Columbia

Astragalus americanus (Hook.) M.E. Jones
American milk-vetch (American milkvetch)
Fabaceae (Pea family)

Introduction to Vascular Plants

© Bryan Kelly-McArthur  Email the photographer   (Photo ID #74753)

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Distribution of Astragalus americanus
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Species Information

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Perennial herb from a woody stem-base, often somewhat rhizomatous; stems solitary to several, erect, 30-100 cm tall, often hollow, mostly unbranched, the lowermost nodes leafless, greenish, glabrous or with sparse, long, soft, unbranched hairs.
Alternate, pinnately compound, 9-17 cm long, short-stalked; leaflets 9 to 17, egg-shaped to elliptic-oblong, rounded at the tip, sparsely hairy below, glabrous above, 2-6 cm long; stipules 1-3 cm long, oblong, not joined, bent downwards.
Inflorescence a loose, axillary raceme of 10 to 25 (40) nodding, pea-like flowers, the racemes 2-9 cm long on stalks equalling or shorter than the leaves; corollas (8) 10-15 mm long, white or yellowish-white, the keel-tip often purplish, the banner slightly longer than the wings, which are shorter than the keel; calyces bell-shaped, 4-5 mm long, glabrous except for the long, fringing hairs of the very short, triangular teeth.
Pods, ellipsoid-inflated, drooping on long (5-10 mm) slender stalks, membranous, shiny, glabrous or nearly so, 2-3 cm long, 1-chambered.

Source: The Illustrated Flora of British Columbia

Habitat / Range

Moist to mesic meadows, streambanks, thickets and forest openings in the montane and steppe zones; frequent in BC east of the Coast-Cascade Mountains; N to AK, YT and NT, E to PQ and S to SD, MT and CO.

Source: The Illustrated Flora of British Columbia


Ecological Framework for Astragalus americanus

The table below shows the species-specific information calculated from
original data (BEC database) provided by the BC Ministry of Forests and Range.
(Updated August, 2013)

Site Information
Value / Class




Elevation (metres) 79 1065 2200
Slope Gradient (%) 0 13 80
Aspect (degrees)
[0 - N; 90 - E; 180 - S; 270 - W]
1 163 352
Soil Moisture Regime (SMR)
[0 - very xeric; 4 - mesic;
8 - hydric]
3 4 7
Modal Nutrient Regime
Number of field plots
 species was recorded in:
Modal BEC Zone Class
All BEC Zones (# of stations/zone) species was recorded in: BWBS(36), ESSF(9), ICH(1), IDF(6), MS(12), SBPS(3), SBS(2), SWB(3)


The climate type for this species, as reported in the: "British Columbia plant species codes and selected attributes. Version 6 Database" (Meidinger et al. 2008), is not evaluated, unknown or variable.

Synonyms and Alternate Names

Astragalus frigidus (L.) A. Gray p.p.
Astragalus frigidus var. americanus (Hook.) S. Watson
Astragalus frigidus var. gaspensis (Rouss.) Fernald
Phaca americana (Hook.) Rydb. ex Small

Taxonomic and Nomenclatural Links

Additional Photo Sources

General References