By some classifications, the genus Cannabis comprises a single species, hemp (Cannabis sativa), a stout, aromatic, erect annual herb that originated in Central Asia and is now cultivated worldwide. A tall canelike variety is raised for the production of hemp fibre, while the female plants of a short branchier variety are prized as the more abundant source of the psychoactive substance tetrahydrocannabinol (THC), the active ingredient of marijuana. See also medical cannabis.