Monographs Details: Bidens
Authority: Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Description:Genus Description - Heads radiate or discoid, the rays when present few, often 8, sterile, generally neutral, yellow or less often white or pink; invol bracts biseriate and dimorphic, the outer ± herbaceous, often very large, the inner membranous, often striate; receptacle flat or slightly convex, its bracts narrow, flat or nearly so; disk-fls perfect and fertile; style-branches flattened, with externally hairy, usually short appendage; achenes flattened parallel to the invol bracts, but not (or scarcely) winged, or sometimes almost regularly tetragonal, rarely subterete; pappus of (1)2–4(6) awns or teeth, commonly retrorsely barbed, but sometimes antrorsely barbed or even barbless, in a few spp. obsolete; herbs (ours) with opposite, simple to dissected lvs. 200, cosmop.
Thelesperma megapotamicum (Spreng.) Kuntze, of the Great Plains, has been reported as adventive in Ill. and Mo. It is a glabrous perennial with the lvs once or twice pinnatifid into slender segments; the discoid (or inconspicuously radiate) heads terminate long, naked peduncles; the outer invol bracts are very short, and the inner ones are connate to the middle or above; the wingless achenes have a pappus of 2 retrorsely barbed awn-scales. (T. gracile)