Bidens bipinnata L.
CW = 3
MOC = 58
Family - Asteraceae/Heliantheae
Habit - Annual forb, usually taprooted.
Stems - Ascending to erect, to 60 cm, glabrous, 4-angled, dichotomously branching.
Leaves - Opposite, petiolate, deeply 2-3x pinnatifid or pinnate, glabrous or with a few sparse hairs, to 20 cm long, 12 cm broad. Petiole to 10 cm long, slightly winged. Ultimate divisions acute to acuminate.
Inflorescence - Solitary terminal heads or loose clusters of heads. Peduncles elongating in fruit to 10 cm long, glabrous or sparsely pubescent.
Heads - Discoid or sometimes with a few ray florets. Involucre 5 mm long, the outer series of 7-10 bracts 3-5 mm long, ascending to more commonly spreading, mostly not leaflike, linear to narrowly oblong-oblanceolate, the margins entire but usually with minute, ascending hairs, the outer surface glabrous; the inner series of 8-12 bracts 4-9 mm long, narrowly lanceolate to linear, glabrous. Chaffy bracts narrowly oblong to linear (elongating somewhat as the fruits mature), usually with a minute fringe of white hairs at the otherwise greenish tip. Receptacle flat.
Flowers - Ray florets 1-5 per head, sterile, sometimes entirely absent. Ligule yellow, inconspicuous, 2-4 mm long, 2 mm broad, rounded at apex, glabrous. Disk florets 12-27 per head, fertile, the corollas 1-2 mm long, yellow. Corolla tube 3 mm long, 5-lobed, glabrous, orange. Lobes acute, 0.5 mm long, glabrous. Stamens 5, adnate near base of corolla tube. Anthers connate around style, included, reddish, 1.1 mm long. Style bifurcate, barely exserted, yellow. Pappus of 2-4 awns 1-4 mm long, these with retrorse barbs, erect to slightly spreading at fruiting.
Fruits - Achenes 10-18 mm long, linear, strongly 4-angled (more or less square in cross-section), awned with persistent pappus, the angles glabrous or with a few minute, stiff, ascending hairs (these denser in immature fruits), the faces each with a pair of slender longitudinal grooves, dark brown to black, often somewhat mottled, glabrous.
Flowering - August - October.
Habitat - Open woods, glades, pastures, open rocky ground, thickets, waste ground, roadsides, railroads.
Origin - Native to the U.S., and tropical regions around the globe.
Lookalikes - The leaves can appear similar to some ferns (e.g. Cystopteris); however, all ferns lack flowers. B. bipinnata is also typically much taller than Cystopteris.
Other info. - This plant is reasonably common in Missouri, most often found south of the Missouri River. It occurs throughout the southeastern half of the U.S. and ranges into Canada as well. It tolerates a wide range of moisture regimes, occurring in habitats from bottomlands to dry glades. The flowering heads are inconspicuous, having ray florets which are small and often missing entirely. The genus name Bidens means "two teeth", referring to the awns of the pappus and fruit (other species only have two awns). Because of the awns, the fruits will cling to most anything, including fur as well as socks and other clothing, thus distributing the plant quickly to new locations. The plant is not stout and becomes droopy and wilted-looking in direct sun.
Photographs taken at the Parkville Nature Sanctuary, Platte County, MO., 8-12-00, and in the Ozark Scenic Riverways, Shannon County, MO., 8-17-03 (DETenaglia); also at Klondike County Park, St. Charles County, MO, 8-17-2008, along the Katy Trail near Augusta, St. Charles County, MO, 8-3-2015, along the Katy Trail near Dutzow, Warren County, MO, 7-10-2018 and 8-16-2020, and along the Katy Trail near Marthasville, Warren County, MO, 9-5-2019 (SRTurner).