Bidens vulgata Greene
CC = 1
CW = 0
MOC = 22
Family - Asteraceae/Heliantheae
Habit - Taprooted annual forb.
Stem - Ascending to erect, to 1.5 m, glabrous or inconspicuously pubescent with sparse, cobwebby hairs, mostly at the nodes.
Leaves - Opposite, all similar, short- to more commonly long-petiolate, the blade 3-15 cm long, broadly ovate-triangular in outline, all except rarely those of the uppermost leaves 1 time ternately or pinnately divided or compound with 3-5 segments or discrete leaflets. Leaflets lanceolate to narrowly ovate, tapered at the base, each with a well-developed stalk (this sometimes narrowly winged), tapered to a sharply pointed tip, the margins usually sharply toothed, sometimes minutely hairy, the surfaces glabrous or the undersurface sparsely to moderately pubescent with minute, fine hairs.
Heads - Inflorescences of solitary terminal heads or appearing in loose, open clusters. Heads discoid, rarely nodding at fruiting. Involucre with the outer series of 10-21 bracts 10-20 mm long, ascending to spreading, leaflike, linear to narrowly oblanceolate, the margins entire but with short, spreading hairs, at least toward the base, the outer surface glabrous or sparsely to moderately pubescent with minute, fine hairs, especially toward the base; the inner series of 8-14 bracts strongly ascending, 5-9 mm long, oblong to narrowly ovate or ovate, glabrous. Chaffy bracts narrowly oblong to oblong-lanceolate, with narrow to broad, yellowish margins but sometimes purplish-tinged at the tip.
Florets - Ray florets absent or 1-5, the corolla inconspicuous, 2-4 mm long, yellow. Disc florets 40-100(-150), the corollas 2.5-4.0 mm long, yellow. Pappus of 2 awns 3-7 mm long, these with downward-pointed barbs, erect to somewhat spreading at fruiting.
Fruits - Achenes 5-12 mm long, wedge-shaped to oblong-obovate, awned, 1 or both faces sometimes with a fine longitudinal nerve or ridge, the angles with minute, stiff, usually ascending hairs, the faces dark brown to black, glabrous or sparsely pubescent with fine, appressed hairs.
Flowering - August - October.
Habitat - Streambanks, pond margins, sloughs, ditches, moist open disturbed areas.
Origin - Native to the U.S.
Lookalikes - Bidens frondosa, also B. tripartita, B. discoidea.
Other info. - This is one of the less common species of Bidens in Missouri, though by no means rare. The flowers lack showy ray florets and are easily overlooked. It occurs in scattered locations in the state, primarily in or near floodplain regions of the large rivers. Its U.S. distribution is concentrated in the upper Midwest and New England, with some populations also found in the northwest.
Photographs taken at Shaw Nature Reserve, Franklin County, MO, 8-31-2007, Frontier County Park, St. Charles County, MO, 10-7-2013, and Creve Coeur Lake Park, St. Louis County, MO, 9-17-2019 (SRTurner).