Northern Prairie Wildlife Research Center
The western 3/4ths of North Dakota is home to creamy poison-vetch. A true plains dweller, the plant is seldom found outside the band of grasslands that stretch from Saskatchewan to Texas and eastern New Mexico.
Creamy poison-vetch is perennial from a branched caudex (thickened stem base) atop a heavy taproot. Plants have a clumped appearance and are covered with tiny, appressed hairs. Leaves can be up to 6 inches long. Each bears 10-30 inch-long leaflets arranged pinnately (like two combs held back-to-back). Inch-long flowers occur in racemes at the ends of stalks about 2-3 inches long. Each raceme bears 20-70 yellowish-white flowers with purplish lines or tips. Flattish legumes (pods) are about an inch long and are filled with dark brown seeds.
Look for creamy poison-vetch in June on clayey soils in native prairie pastures that are lightly or moderately grazed. This plant is a notorious selenium-accumulator that seems to require this element in the soil in order to achieve proper growth. Such plants may cause blindness, hemorrhaging, or paralysis in livestock, but acute poisoning is rare and only caused by single, massive doses.
Creamy poison-vetch is a member of the economically important bean family (Fabaceae). Fab means "bean" in Latin. The generic name Astragalus is an old Greek name of some leguminous plant, and also of the ankle bone. Worldwide, there are about 1,500 species of Astragalus; most are found in the North Temperate and Arctic zones. The specific epithet racemosus means "racemose" in botanical Latin. A raceme is an elongated inflorescence with pedicillate flowers. Creamy poison-vetch was first described for science by the eminent German botanist Frederick Traugott Pursh (1774-1820) in his monumental Flora Americae Septentrionalis of 1814. Pursh was the first to publish on the many new plants collected by Lewis and Clark.