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The locoweed common name is used to describe any plant that produces swainsonine. In North America those include Oxytropis and Astragalus, both in the Pea family. Not all varieties are poisonous. Swainsonine is a toxin that causes losses in the livestock and equine industries. The term loco is from Spanish roots and generally means crazy in English. The signs of ”locoism” include aggression, hyperactivity, salivation, increasing miscoordination, seizures, and death.
Oxytropis is widely distributed mainly west of the Mississippi and throughout all of Canada and Alaska. The eastern US seems to have been spared so far. Some of the more dispersed varieties include; nodding locoweed, purple locoweed, field locoweed and showy locoweed. Oxytropis is a perennial herb native to North America that grows 6-12in. tall. Leaves are 2 to 8in. long and the stems produce many flowers each with many seeds. Flower color can be white, purple or yellow. It reproduces from seed and prefers well drained sandy loam in bright light.
Astragalus is a large genus of about 3000 species. It is mostly know as locoweed and milkvetch depending on the species. Not all varieties contain the toxin swainsonine and some are used as forage for livestock. Many of these herbs are used in Chinese medicines and are sold commercially as an antioxidant. It is 18-36in. tall perennial, has hairy stems with leafs made up of 12-18 pairs of leaflets. The flower color can be purple, white or yellow. The medicinal portion is the root and is usually harvested from 4 year old plants.