This common annual is widely cultivated (as the "sunflower"), but it also escapes and appears naturalized along disturbed rights-of-way and similar sites. Though probably originating in the southern Great Plains, annuus became domesticated for oil and other uses by native people in eastern states (C.B. Heiser in Ford 1985; Smith 2006). Selection has increased seed size and head size, especially during the past century or so, but within a few generations of naturalization cultivars revert to wilder types. Maximum heights are generally 2-3 m, but world records are reportedly 7.3 to 8.2 m (GuinessWorldRecords.com and Wikipedia). Varieties have not been recognized in recent treatments; but see notes on hybrids under petiolaris (2n = 34 in both) and with tuberosus.