Broad-keeled Milkvetch - Astragalus platytropis
MNPS Threat Rank
Broad-keeled milkvetch is a small perennial herb without prolonged stems; all leaves are clustered at the base of the plant on short branches of the rootcrown clothed with old leaf stalks. Pinnately compound leaves, 1-9 cm long, have 7-15 oblong to elliptic, often blunt-tipped leaflets. Foliage is sparsely covered with gray or silver hairs. Spreading flower stalks arise from amongst the leaves and bear 3-9 flowers near the tip. Whitish, pea-like flowers are 6-9 mm long with an upper petal that is barely reflexed and nearly the same length as the others. The calyx is 3-5 mm long and sparsely covered with white or black hairs. Inflated, egg-shaped fruits are papery, purple-mottled, and 15-33 mm (ca. 1 in) long. Fruits that resemble small Chinese lanterns are usually found on the ground near the base of the plant.
Flowering in April and May, fruiting in June
It resembles the widespread Astragalus miser var. hylophilus in vegetative condition, except that it has leaves with petioles that are usuallly much longer than the blade, and typically has a trailing growth form. The only other species of milkvetch in Montana with inflated pods that lie along the ground is Astragalus crassicarpus, but it differs in having a papery pod with a mottled pattern rather than a very fleshy green or red pod. papery, purple-mottled fruit are diagnostic.
Montana and central Idaho, southward through Nevada to eastern California, and at the edge of its range in western Wyoming.
Observations in Montana Natural Heritage Program Database
Number of Observations:
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(Observations spanning multiple months or years are excluded from time charts)
Limestone- or crystalline-derived soils in open grasslands and sagebrush steppe in the valleys and montane zone.
- Additional ReferencesLegend: View Online Publication
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- Heidel, B.L. and J. Vanderhorst. 1996. Sensitive plant species surveys in the Butte District, Beaverhead and Madison Counties. Unpublished report to the Bureau of Land Management. Montana Natural Heritage Program, Helena, Montana.
- Lesica, P. 1992. Sensitive plant inventory of the Birch Creek Grazing Allotment, BeaverheadCounty. Uunpublished report to the Bureau of Land Management. Montana Natural Heritage Program, Helena. 3 pp.
- Lesica, P. 1994. Sensitive plant survey of BLM lands along the Big Hole River and in the Whitehall Valley. Montana Natural Heritage Program, Helena, MT. 13 pp.
- Lesica, P., M. T. Lavin, and P. F. Stickney. 2012. Manual of Montana Vascular Plants. Fort Worth, TX: BRIT Press. viii + 771 p.
- Schassberger, L.A. 1989. [Field surveys of the Pioneer Mountains, 6-9 June (Arabis fecunda).]