Field Milkvetch
Astragalus agrestis Dougl.
Family: Fabaceae, Pea
Genus: Astragalus
Synonyms: Astragalus dasyglottis
Other names: purple milkvetch
Nomenclature: agrestis = of a field, rustic
Nativity / Invasiveness: Montana native plant
Poisonous plant
No medicinal data
Description

General: low, short-flat-hairy perennial with long rootstocks from a buried crown. Stems numerous, slender, creeping to erect, 10-30 cm tall.

Leaves: alternate, 4-10 cm long, the 11-19 leaflets linear-lanceolate to oblong-lanceolate, often slightly notched at tips, 1-2 cm long. Stipules linear to ovate, blunt-tipped, usually joined around stem at the base.

Flowers: about 7-20 in head-like clusters, 1.5-2.5 cm broad and as long, from leaf axils. Main flower stalks shorter to longer than the leaves. Flowers erect, about 17 (13-19) mm long, the individual stalks thick, scarcely 0.5 mm long. Calyx about half the length of the corolla, with grayish to blackish, flat to spreading hairs, the teeth linear, somewhat shorter than the tube. Corolla usually purplish, or the wings whitish, the banner narrow, longer than the slender wings which are about 4 mm longer than the slightly pointed keel. June-August.

Fruits: pods, stalkless, erect, about 1 cm long, grayish- to blackish-stiff-hairy, ovoid, cordate in section, 2-celled by the deep groove of the lower seam.


Distribution

Moist spots in sagebrush plains and montane meadows to alpine slopes, in most parts of MT. Also from Yukon southward, on the e. side of the Cascades, from B.C. to n. CA, NM, e. to Manitoba, MN, IA, and KS, and in e. Asia.
Poisonous Properties

A large, diverse number of milkvetches endemic to North America are considered toxic to both livestock and wildlife, often producing behaviors in poisoned animals described as "crazy", hence the common name "locoweed" ("loco" is Spanish for "crazy") often given to many species. The poisonous species have been historically divided into three groups: those species that produce nitrotoxins, those that accumulate the element selenium, and those that produce alkaloids known as "locoine" or "swainsonine". Nitrotoxins, such as 3-nitro propanol, are produced by a large number of species in the western North America, but only a relatively few species have high enough concentrations to actually poison livestock grazing on them. The toxic nitro-containing compounds as well as their glycoside derivatives disrupt normal functions of the central nervous system, often leading to paralysis and death. Some 25 North American species of Astragalus have been identified as selenium accumulators. These species concentrate the element selenium (Se) in their tissues to toxic levels. The third type of poisoning and probably the most severe, called "locoweed poisoning" or "locoism", is caused by several species of Astragalus and a few species of Oxytropis which synthesize the alkaloid swainsonine. When eaten, swainsonine inhibits cellular enzymes (mannosidases) and produces an intoxicating, addictive response, ultimately leading to weight loss and impaired locomotor functions, resulting in ataxia and death.


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