Bidens polylepis Blake

Bidens polylepis plant

Family - Asteraceae

Stems - To +2m tall, erect, branching, multiple from base, herbaceous, rooting at lower nodes, often purplish or mottled, 4-angled, (the angles rounded), fluted, glabrous to sparse antrorse pubescent, from fibrous roots.

Bidens polylepis stemStem at a node.

Leaves - Opposite, petiolate. Petioles to +/-3cm long, with an adaxial groove (the groove sparsely pubescent). Blades pinnately divided. Ultimate divisions serrate, lanceolate to linear-lanceolate, the terminal division being the largest, to 10cm long, 1.5cm broad, deep dull green and very sparse antrorse pubescent above, light green and antrorse pubescent below. Leaves reduced upward.

Bidens polylepis leaves

Inflorescence - Loose cymose arrangement of flower heads.

Involucre - Flat, to 2.3cm broad. Bracts biseriate. Outer phyllaries +/-15, with fimbriate margins, linear, acute, often twisted, to +1cm long, 1.2-1.4mm broad, pubescent externally, often with revolute margins. Inner phyllaries yellowish, with dark purple apices, ovate-lanceolate, entire, glabrous, 6-7mm long, 2-3mm broad, erect in fruit.

Bidens polylepis involucreInvolucre.

Ray flowers - +/-8 per flower head, sterile. Ligule to 3cm long, +/-1cm broad, yellow, glabrous, the apex blunt to very shallowly 2-3 notched. Corolla tube antrorse pubescent. Achene reduced, compressed, with barbed margins, 1mm long, rectangular.

Disk flowers - Corolla yellowish, 5-lobed. Corolla tube constricted in lower 1/2, funnelform in upper 1/2, glabrous, to 4mm long. Corolla lobes acute, spreading to erect, .7mm long. Stamens 5, adnate at apex of corolla tube constriction. Filaments to 1.2mm long, glabrous, pale yellow. Anthers connate around style, purplish-brown, exserted, to 2.1mm long. Style typically not exserted beyond anthers, bifurcate, yellow in apical portion (stigma). Achenes (in flower) white, compressed, 3-sided, antrorse pubescent, with barbed margins, becoming obovate in fruit, dark greenish, +/-4mm long, 3mm broad. Pappus of two rounded shallow awns. Chaff compressed, to 7mm long, 1mm broad, translucent but yellowish in upper 1/2 and with a purple tip, glabrous, subacute.

Bidens polylepis flowers

Flowering - August to October.

Habitat - Wet prairies and meadows, swampy woods, ditches, waste ground, roadsides, railroads.

Origin - Native to U.S.

Other info. - This species is common throughout Missouri. It can be seen growing along many roads and highways. The ligules in the first picture above appear to be two-toned but are really solid yellow when seen in nature. This is a weedy species which is locally abundant but is also very striking and visited by many flying insects.
Steyermark lists two varieties for the plant based on awn barb direction. Variety polylepis has antrorse awn barbs. Variety retrorsa Sherff has, you guessed it, retrorse awn barbs.

Photographs taken off Hwy C, Carter County, MO., 8-31-03.


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