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Flexile Milk-vetch
Astragalus flexuosus (Hook.) Dougl. ex G. Don
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Family: Fabaceae,
Pea
Genus: Astragalus
Description
General: perennial, short-flat-hairy, with a branched crown
and slender, erect to creeping-based stems 40-70 cm long.
 Leaves: alternate, 4-12 cm long, very short-stalked, the
15-21 leaflets linear-oblanceolate to oblong, 5-22 mm long,
often short-stalked at base, rounded to notched, finely
flat-hairy on the lower surface but usually hairless on the
upper, the axis often flexile. Lower stipules 2-4 mm long,
ovate-lanceolate, and slightly joined, the upper ones more
narrowly lanceolate, 3-5 mm long, and not joined.
 Flowers: about 10-30 in elongate loose clusters which in
fruit are usually at least equal to the 5-10 cm main stalks.
Individual flower stalks 1-3 mm long. Calyx grayish-flat-stiff-
hairy, 4-5 mm long, the slender teeth 1/4-1/3 as long as the
tube. Corolla nearly white and merely purplish-tinged to light
lavender-purple, 6-10 mm long, the rounded keel 5-7 mm
long, much shorter than the wings.
Flowering time: June-July.
 Fruits: pods, with a stalk-like support scarcely 1 mm
long and concealed by the calyx tube, the body narrowly
oblong, 12-21 mm long, 2-3.5 mm wide, pointed at each
end, almost straight and round in section.
Distribution
Plains and hills, often on rather strongly alkaline soil, in w.
and c. parts of MT. Also along the e. slope of the Rocky
Mts., from Alberta and Sask. to NM, MN, and KS.
 Possibly Toxic plant: see below.
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(click on image for full size)
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(click on images for full size)
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".
Aliphatic nitrotoxins, such as 3-nitro propanol, which 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.
Varieties:
Our specimen belong to var. flexuosus (Hook.) Dougl. ex G. Don. |
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