Bidens pilosa has been treated as a widespread variable species of warmer American regions (with 2n = 24, 36, 48 or 72), but a narrower concept may be warranted (Ballard 1986; FNA 21, W, Y). It is an annual or short-lived perennial with whitish rays, and sometimes has horticultural use. Plants of pilosa introduced to Africa (as "blackjack") and Asia (as the "soldier vegetable" in Vietnam) have become widely used for nutrition (with a resinous flavor) or for medicine (e.g. Silva et al. 2011). The only known coll. from Ky. appears to be a rare waif: J.W. Thieret, 3 Oct 1977, weed among low planted junipers, rest area of Interstate 75 between Berea & Richmond (KNK). This coll. is probably referable to B. alba var. radiata (Schultz-Bip.) Ballard ex T.E. Melchert. That taxon has more rays and phyllaries (2n = 48) and extends north more frequently than typical pilosa, which usually lacks rays (2n = 72).