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Annuals.  Stems are often branching from near plant base.  Typical height is 2 to 3 feet.

Inflorescences consist of a few flower heads located at the summits of stems or at ends of branches.

Flower heads are typically discoid, or less often radiate with a few small, yellow rays (4-8 mm long); erect (not nodding).  Ray florets, when present, are neuterDisc florets are bisexual and fertile, the corollas yellow, gradually widened toward the summit; strongly attached to the cypselae.   Involucral bracts are in two series: an inner series - short, yellowish, petal-like, and an outer series -  longer, narrower, green, leaf-like.

Basal leaves are usually absent at flowering.    Stem leaves are opposite, lanceolate or oblanceolate, lacking petioles or gradually tapered to winged petioles; not divided into leaflets, coarsely toothed and/or irregularly lobed.

Cypselae are dark brown to black, compressed, weakly 4-angled,  flat or concave at the summit, narrowed toward the base, the faces lacking minute tubercules.  The pappus is of minutely barbed awns (2-3 mm long).

Plants of pond and stream shores, edges of marshes, wet meadows.  Flowers late August to late September.  Native.

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Similar species:  Bidens connata, B. frondosa, B. cernua.

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Note:  Some researchers consider B. connata and B. tripartita to be the same species.  Haines (2011) makes a convincing argument that both taxa should be recognized as different species, based on subtle differences in floral and fruit morphology; such as whether the disc corollas become abruptly widened or gradually widened apically; whether disc corollas are pale yellow or yellow-orange; whether faces of the cypselae are tuberculate or not; whether the disc corollas are persistent in fruit or not.  (As noted above.)  Also, B. tripartita tends to have larger heads with more disc florets per head (20-60 on avg.) compared with 20-40 on avg. for B. connata.

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