any of several perennial plants (genera Astragalus and Oxytropis) of the pea family, which are common in W North America and cause the loco disease of cattle, sheep, and, esp., horses
See locoweed in American Heritage Dictionary 4
(lōˈkō-wēdˌ)
noun
Any of several plants of the genera Oxytropis and Astragalus in the pea family, which are widespread in the western and central United States and cause severe poisoning when eaten by livestock. Also called crazyweed, loco1.