On a ridge above Lower Hat Creek (Shasta County CA) I found a patch of wooly locoweed (Astragalus purshii). The genus, containing a large number of species, not all of which are poisonous, is found in the Western United States and Western Canada. A. purshii, also commonly called woolypod milkvetch or Pursh’s sheeppod, is a legume belonging to the pea family. It is found mostly in open, dry areas with rocky, thin soils (lithosols).
Many locoweeds are difficult to distinguish and are easily confused with vetches. However, the wooly locoweed is quite distinctive. The perennial plant forms a low mat or cushion that rarely grows more than six inches in height. Depending on location the pea-like flowers can be pink, rose, purple or white. The gray-green leaves are pinnately compound. The entire plant is covered in dense white hairs which makes it look silvery. The hairy legume, or seed pod, resembles a small rabbit’s foot. When ripe, the seed pod contains small black seeds which are wooly locoweed’s main method of propagation.
Wooly locoweed (“loco” from the Spanish for “crazy”) is poisonous because it contains an alkaloid, swainsonine, that affects livestock. The effects of swainsonine are cumulative and many plants must be eaten over many days before the symptoms appear. Once symptoms are noticed animals rarely recover completely. Locoweed ingestion causes a lack of coordination and muscle control, a slow swaggering gait (particularly in horses), distorted vision and unpredictable behavior, especially when aroused or excited. Livestock usually avoid eating locoweed, but once they do eat it they become “hooked” and continue to addictively eat locoweed.
Because of its poisonous nature wooly locoweed is not used for culinary or medicinal purposes. The Thompson Indians of British Columbia did make a decoction of A. purshii for use as a body and hair wash. I assume they did not drink it but only used the locoweed externally.
Wooly locoweed is a pretty little plant that I always enjoy finding.