Astragalus is a large genus of over 3,000 species of herbs and small shrubs, belonging to the legume family Fabaceae and the subfamily Faboideae. It is the largest genus of plants in terms of described species. The genus is native to temperate regions of the Northern Hemisphere. Common names include milkvetch, locoweed and goat's-thorn. Some pale-flowered vetches are similar in appearance, but they are more vine-like than Astragalus.

The inverted repeat-lacking clade (IRLC) is a monophyletic clade of the flowering plant subfamily Faboideae. Faboideae includes the majority of agriculturally-cultivated legumes. The name of this clade is informal and is not assumed to have any particular taxonomic rank like the names authorized by the ICBN or the ICPN. The clade is characterized by the loss of one of the two 25-kb inverted repeats in the plastid genome that are found in most land plants. It is consistently resolved in molecular phylogenies. The clade is predicted to have diverged from the other legume lineages 39.0±2.4 million years ago. It includes several large, temperate genera such as Astragalus, Hedysarum, Medicago, Oxytropis, Swainsona, and Trifolium.