Bidens tripartita L.
swamp beggars' ticks
Erect, glabrous or almost glabrous annual, 10-80 cm tall. Stems angled, branched above to form infl. Lvs petiolate, usually simple and not lobed, sometimes deeply 1-pinnatisect with 3-5 segments, 3-10-(20) cm long; lamina or segments narrowly ovate-elliptic to lanceolate, coarsely and often unevenly serrate, acuminate. Upper cauline lvs becoming smaller, shortly petiolate or apetiolate, not lobed and less distinctly serrate. Capitula 4-10 mm diam. Outer involucral bracts 3-4, foliaceous, glabrous, linear, 6-12 mm long; inner bracts many, membranous, ovate-elliptic to ovate-triangular, 5-8 mm long, with dark lined centre and pale margins. Receptacular scales similar to inner bracts but narrower. Florets all ⚥, tubular, yellow-orange. Achenes flattened, ovate-cuneate to obtriangular, with 1 slender to prominent rib on each face, dark brown, ciliate and otherwise glabrous to sparsely hairy, 5-8 mm long; awns 2-4, often unequal, 0.5-2.7 mm long.
S.: West Coast from vicinity of Karamea to vicinity of Hokitika.
Temperate regions 1975
Swamps, stream edges, damp waste places.
FL Feb-Mar.
The achenes of B. tripartita are similar to those of B. frondosa, illustrated in Fig. 21, but usually one or both facial ribs are extended into short awns. N.Z. material has previously been referred to B. connata Willd., but recent American Floras place B. connata in synonomy under B. tripartita. N.Z. material differs from typical N. American and European plants of B. tripartita in having smaller heads with fewer outer bracts. As in many other Bidens spp., both rayed and rayless variants occur in B. tripartita, but all N.Z. material I have seen lacks rays. Early references to B. tripartitus in N.Z. are the result of misidentification of B. frondosa.
