Locoweed Astragalus and Oxytropis spp. The plant Astragalus and Oxytropis are leguminous perennials found in large concentrations in western North America. Many species of Astragalus are not poisonous and are good rangeland forage plants. However, within the same species, concentrations of toxicants can vary widely from plant to plant so all locoweeds and milk vetches should be approached with caution and assumed potentially dangerous to livestock. Their leaves are alternate and pinnately compound.
Flowers are leguminous and the fruit is a legume pod with kidney shaped seeds.
The pod is often conspicuously enlarged causing the seeds to rattle in it when ripe, hence the common names, rattlebox and rattleweed, that are often assigned to it. The keel petal of Oxytropis tends to be long and pointed whereas that of Astragalus tends to be blunter. Note that these two closely related genuses also carry many of the same toxins.