This thorny shrub has become a locally abundant invader across much of northern North America, but it remains virtually unknown in southern states (K, W, SE). In Ky. it has been planted in some residential areas since 1960 or earlier, but there has been little naturalization. There has been some confusion with the much more invasive davurica; see notes under that name (also W). R. cathartica can hybridize with some other introduced species of Rhamnus (Gil-Ad & Reznicek 1997). Rhamnus sensu stricto differs from Endotropis as follows (FNA 12, W): leaves usually opposite to subopposite (versus usually alternate); blades with 2-8 pairs of secondary veins (versus 4-11); plants usually up to 2-10 m tall (versus 0.5-3 m), and usually with thorny branches (versus not thorny). See also notes under Frangula caroliniana on concepts of these three closely related genera. .