This tall annual is widespread in temperate regions of North America. It is generally known as "giant ragweed" but the old common name "buffalo-weed" (F) suggests a prehistoric association with ungulates. It is often browsed by deer (Atwood 1941, Sickels & Simpson 1985; and pers. obs.),and it can provide nutritious forage for livestock (Bassett & Crompton 1982). In 1914 Gm called it "horse-weed... often cut for horses, and said to be a remedy for slobbering... sometimes cured and ground for feed... being rich in nitrogenous material." There is also evidence that seeds were eaten, cultivated and even selected for larger size by native people in some regions (as cited by Y); see also Ford (1985). However, trifida is a major source of allergenic pollen for humans (Bassett & Crompton 1982, White & Bernstein 2003). It is one of tallest herbaceous plants, at least in North America. It is often 3-4 m and the local record may be ca. 6 m in Hamilton Co., Ohio (D. Boone, pers. comm.). One has been measured at 6.41 m in Texas (Mims 2010); see also notes under Helianthus annuus, Cannabis sativa and Lactuca biennis. Varieties have been described, but the species is considered relatively uniform (2n = 24) and hybrids have not been documented in Ky. Var. integrifolia (Muhl.) Torr. & Gray was reported from BALL by Anderson (1947; check Iowa State Univ.). Var. texana Scheele could be expected as an adventive from the southwest, but the only Ky. report appears to have been erroneous (M).