Astragalus and Related Genera—Ecological Considerations
This chapter reviews of literature and a summary of the experiences and observations of the authors on the ecology of species in the Astragalus and Oxytropis genera and three toxicoses associated with the genera. Those toxicoses are swainsonine, nitro toxins, and selenium. Astragalus is distributed mainly in arctic and temperate portions of the Northern Hemisphere but extends south into both the Paleotropics and Neotropics. Soils occupied by plants of Astragalus vary texturally from silts and clays through sands, gravels, and boulders. Astragalus species are seldom dominants or codominants in a vegetative type. Nitro-containirig species of Astragalus are indigenous throughout the temperate and subalpine regions of the Northern Hemisphere and from Ecuador southward to Argentina in South America. Nitro compounds are found primarily in the green leaves of nitro-containing species of Astragalus. The selenium content of accumulator species of Astragalus is influenced by climatic conditions, selenium content of the soil, and stage of growth.