4. Bidens bipinnata L. (Spanish needles)
Pl. 274 i, j;
Map 1152
Plants annual,
terrestrial, usually with taproots. Stems 15–60(–150) cm, erect or ascending,
glabrous or sparsely to moderately pubescent with minute, more or less
spreading hairs. Leaves all more or less similar, short- to long-petiolate,
opposite, the blade 3–20 cm long, lanceolate to ovate in outline, all except
rarely those of the uppermost leaves 2 or 3 times pinnately lobed, divided,
and/or compound into 7 to numerous ultimate lobes or segments, these lanceolate
to obovate, mostly angled or tapered at the base, without a stalklike base,
tapered to a sharply pointed tip, the margins otherwise entire or coarsely
few-toothed, sometimes minutely hairy, the surfaces glabrous or the
undersurface sparsely and minutely hairy along the main veins. Inflorescences
of solitary terminal heads or appearing in loose, open clusters, the heads discoid
or appearing discoid, not nodding at fruiting. Involucre with 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. Ray florets absent or 1–5, the corolla inconspicuous, 2–4 mm long, yellow.
Disc florets 12–27, the corollas 1–2 mm long, yellow. Pappus of 2–4 awns 1–4 mm
long, these with downward-pointed barbs, erect to slightly spreading at
fruiting. Fruits 10–18 mm long, linear, strongly 4-angled (more or less square
in cross-section), 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. 2n=24,
72. August–October.
Scattered,
mostly south of the Missouri River (eastern U.S. west to Nebraska and Arizona;
Canada, Mexico, Central America, South America, Asia, Madagascar, Malesia,
Australia). Upland prairies, glades, openings of mesic to dry upland forests,
bottomland forests, and banks of streams and rivers; also ditches, pastures,
fallow fields, gardens, railroads, roadsides, and open, disturbed areas.
The natural
range of this species is not well understood as it long ago became established
as a weed in many parts of the world. Sherff (1955) speculated that the native
range prior to the period of European expansionism was in the eastern United
States and eastern Asia. The distributional summary above does not attempt to
discriminate native vs. adventive components of the overall range of the
species.