合欢草（学名：Desmanthus virgatus）为豆科合欢草属下的一个种。

Desmanthus virgatus is a species of flowering plant in the legume family that is known by many common names, including wild tantan, prostrate bundleflower, dwarf koa, desmanto, acacia courant, acacia savane, pompon blank, adormidera, brusca prieta, frijolillo, ground tamarind, guajillo, guashillo, huarangillo, langalet, petit acacia, petit cassie, petit mimosa, virgate mimosa, and slender mimosa, as well as simply desmanthus. It is native to the American tropics and subtropics but is present elsewhere as an introduced species. In some areas it is cultivated as a fodder and forage crop.