Ambrosia cheiranthifolia is a rare species of flowering plant known by the common names South Texas ambrosia and Rio Grande ragweed. It is native to the coast of South Texas and the Mexican states of Tamaulipas and Coahuila. It occurs in coastal prairie, grassland, and mesquite shrubland habitat. It has declined because its native habitat has been cleared for development, with remaining open savanna invaded by non-native grasses such as buffelgrass (Cenchrus ciliaris). Today there are perhaps 20 populations remaining, but some of these may have very few genetic individuals because the species is clonal, with many cloned plants attached by one rhizome. It is not certain that the plant still exists in Mexico. This is a federally listed endangered species of the United States.