This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol3", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Bidens cernua L. Sp. Pl. 832. 1753. Coreopsis Bidens L. loc. cit. 908. 1753.
Annual; stems glabrous, or hispid, usually erect, branched, 3'-3° high. Leaves sessile and commonly somewhat connate-perfoliate at the base, lanceolate to oblong-lanceolate, usually coarsely and sharply serrate, glabrous, acuminate, 3'-6' long, 1/4'-1' wide; heads numerous, globose, short-peduncled, 1/2'-1' broad, nodding after or during flowering; rays 6-10, short (3"-6"), or none; involucre depressed-hemispheric, its outer bracts commonly ciliate, often large, foliaceous and much exceeding the broad, yellowish-margined membranous inner ones: achenes cuneate, 2" long, retrorsely hispid on the margins; pappus of 2-4 (usually 4), downwardly barbed awns, about half as long as the achene.
In wet soil, Nova Scotia to Hudson Bay and British Columbia, North Carolina, Missouri and California. Also in Europe and Asia. Consists of many races, differing in size. Water-agrimony. Double-tooth. Pitchforks. July-Oct.
Bidens Eatoni Fernald, known only from brackish soil, along the Merrimac River, Mass., has narrower heads and smaller achenes with awns either upwardly or downwardly barbed.
A plant, with all the leaves pinnately divided, growing in the vicinity of Minneapolis, Minn., described as Bidens connata pinnata S. Wats., may be a hybrid with B. aristosa.
Annual; glabrous throughout; stem erect, usually branched, 6'-8° high, purple. Leaves peti-oled, lanceolate or oblong-lanceolate, sharply and coarsely serrate, thin, 2'-5' long, 1/4'-1' wide, apex acuminate, base tapering, the uppermost sometimes sessile, nearly entire and acutish, the lower sometimes with a pair of basal lobes, decurrent on the petiole; heads several or numerous, pe-duncled, 1/2'-1 1/2' broad; involucre campanulate or hemispheric, the outer bracts somewhat exceeding the ovate-oblong, inner ones; rays none, or 1-5 and inconspicuous; disk-flowers orange; achenes cuneate or obovate, hairy and tubercled, or nearly glabrous, keeled, or angled, 2"-3" long, the margins with either erect or retrorse hairs, or both, the 2-4 pappus awns downwardly barbed, half as long as the achene.
In swamps or moist soil, Rhode Island to Ontario, Minnesota, Delaware, Georgia, Kentucky, Missouri and Nebraska. Introduced into Europe. Cuckold. Harvest-lice. Pitchforks. Aug.-Oct.
Annual, glabrous; stem erect, branched, 6'-41/2° high, straw-colored. Leaves short-petioled, or sub-sessile, lanceolate to elliptic-lanceolate, coarsely serrate with mostly smaller teeth than in B. connata, tapering to each end, the petioles broadly margined; heads several or numerous, 1/2"-1 1/2" broad; outer bracts of the involucre linear, spatulate or lanceolate, foliaceous, erect or spreading, often toothed, 2-4 times as long as the head; rays none; corollas mostly 4-lobed, pale greenish yellow; stamens and style included; achenes larger, 31/2"-5 1/2" long, evenly cuneate, very flat; pappus awns commonly 3, downwardly barbed, somewhat shorter than the achene.
In wet soil, Massachusetts to Illinois, North Dakota, New Jersey, West Virginia, Kentucky and Kansas. Leaves thicker and paler than in B. connata. Aug.-Oct.