Bidens bipinnata L.

Spanish Needles

Bidens bipinnata plant

Family - Asteraceae

Habit - Annual forb, usually taprooted.

Stems - Ascending to erect, to 60 cm, glabrous, 4-angled, dichotomously branching.

Bidens bipinnata flowerStem.

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.

Bidens bipinnata leaf1Leaf adaxial.

Bidens bipinnata leaf2Leaf abaxial.

Bidens bipinnata leavesLeaves.

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.

Bidens bipinnata involucreInvolucre.

Ray flowers - Absent or 1-5 per head, sterile. Ligule yellow, inconspicuous, 2-4 mm long, 2 mm broad, rounded at apex, glabrous.

Disk flowers - 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.

Bidens bipinnata flowerFlowering head.

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.

Bidens bipinnata fruitsFruiting head.

Bidens bipinnata fruit3Mature fruits.

Flowering - August - October.

Habitat - Open woods, glades, pastures, open rocky ground, thickets, waste ground, roadsides, railroads.

Origin - Native to 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.

The species is used in traditional Chinese medicine, and in that context is called nianshencao ("stick to the body weed").

Leaves of Bidens species have a distinctive tertiary venation pattern which can be described as disjointed and looping. The appearance has been roughly likened to hieroglyphics.

Bidens bipinnata leavesLeaf venation.

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 along the Katy Trail near Dutzow, Warren County, MO, 8-3-2015 and 7-10-2018 (SRTurner).