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Volume IV (1988) - Flora of New Zealand Naturalised Pteridophytes, Gymnosperms, Dicotyledons
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Bidens L.

BIDENS L.

Annual or perennial herbs. Lvs opposite, simple and entire to pinnately or ternately dissected or compound. Capitula pedunculate, solitary or in loose cymes. Involucral bracts in 2 rows; outer row usually foliaceous; inner row membranous. Receptacle flat or slightly convex; scales present. Either outer florets ligulate, female or sterile, and white, yellow or pink, or all florets tubular and ⚥. Achenes all similar, square or flattened in section but not winged; pappus of (0)-2-5 awns usually with retrorse barbs.

Key

1
Achenes ± linear; outer foliaceous involucral bracts < to slightly > inner membranous bracts
2. *pilosa
Achenes ovate-cuneate to obtriangular; outer foliaceous bracts usually much > inner membranous bracts
2
2
Lower cauline lvs 1-pinnate; capitula 10-20 mm diam.; all achenes with 2 awns
1. *frondosa
Lower cauline lvs simple and not lobed or 1-pinnatisect; capitula 4-10 mm diam.; many achenes with 3-4 awns
3. *tripartita

Up to 230 spp., cosmopolitan. Naturalised spp. 3.

The genus has been monographed by Sherff, E. E., Field Mus. Nat. Hist. Chicago, Bot. 16 : 1-709 (1937), who accepted or described many spp. on characters which are variable within or among populations [Ganders, F. R. and Nagata, K. M., in Grant, W. F., Ed., Plant Biosystematics (1984)]. Recent American Floras place many of the spp. accepted by Sherff in synonomy, and this more conservative approach is followed here.

Fig. 21. Achenes of Bidens. A B. frondosa; B B. pilosa. © All rights reserved. [Image: 4X4D]
Fig. 21. Achenes of Bidens. A B. frondosa; B B. pilosa. © All rights reserved. [Image: 4X4D]
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