Astragalus bisulcatus (Hook.) A. Gray

Astragalus bisulcatus, commonly called two-grooved milkvetch or silver-leafed milkvetch, is a leafy perennial with pea-like flowers. It is native to central and western North America,^[1] and typically grows on selenium-rich soils. It accumulates selenium within its tissues, and when livestock consume it, the selenium can be toxic.^[2]

Description

Astragalus bisulcatus is a herbaceous perennial with a thick woody root-stock, growing 30 to 100 cm tall.^[3] It has numerous simple stems and long pinnate leaves. The flowers are produced in narrow elongated racemes. The flowers are white or purple in color^[4] and bloom in late spring and early summer. The seed pods characteristically are two grooved on the upper surface. The fruits ripen and release their seeds in July and August.^[5] The seeds are dark brown or black, reniform in shape, 4 mm long and 2 mm wide.^[3][6]

Selenium toxicity

Astragalus bisulcatus accumulates large quantities of selenium when grown on soils that have selenium, the plant produces amino acids where sulfur is replaced by selenium.^[7] Most animals avoid Astragalus bisulcatus because of the musky odor of the dimethyl selenium compounds contained in the plants tissues.^[8] Yet, sheep and cattle have indulged in eating the plant, becoming victims of selenium toxicity. Sheep can die in thirty minutes from eating a half a pound of Astragalus bisulcatus, and in 1907 and 1908, approximately 15,000 sheep in Wyoming died with symptoms of either alkali disease or the blind staggers; both of which were outcomes of digesting a large amount of selenium from Astragalus bisulcatus.^[9]

References