Vascular – Exotic
Dicotyledonous Herbs - Composites
The National Vegetation Survey (NVS) Databank is a physical archive and electronic databank containing records of over 94,000 vegetation survey plots - including data from over 19,000 permanent plots. NVS maintains a standard set of species code abbreviations that correspond to standard scientific plant names from the Ngä Tipu o Aotearoa - New Zealand Plants database.
Tall upright annual, up to 2 m tall, with deeply divided leaves, yellow button-like flowers and characteristic flat black seeds with two barbed teeth easily attaching to clothing and hair.
Locally abundant in northern and eastern North island, scattered elsewhere in the North Island and northern South Island as far south as Westland and Christchurch.
Water body margins, swamps, damp waste places and low-lying areas.
Erect, glabrous or almost glabrous annual, 20-200 cm tall. Stems angled, branched above to form infl., and sometimes from base. Lvs petiolate, 1-pinnate, with 1-2 pairs of leaflets and a slightly larger terminal leaflet; leaflets sessile or shortly petiolulate, narrow-ovate to lanceolate, coarsely or unevenly serrate, acuminate, (1)-2-13 cm long. Upper cauline lvs becoming smaller, shortly petiolate, and often simple and not lobed or 3-lobed. Capitula 10-20 mm diam. Outer involucral bracts 4-9, foliaceous, usually ciliate at least at base, sometimes glabrous, linear to narrowly oblong-obovate, (10)-15-30 mm long; inner bracts many, membranous, triangular to subulate, 6-10 mm long, with dark lined centre and pale margins. Receptacular scales similar to inner bracts but narrower. Florets usually all ☿, tubular, yellow-orange, rarely a few orange ray florets present. Achenes flattened, ovate-cuneate with 1 slender rib on each face, dark brown, ciliate, and otherwise glabrous to sparsely hairy, 6-10 mm long; awns 2, 2.5-4.5 mm long.
Non-flowering plants are superficially similar to cannabis. Differs from the two other Bidens species by the two toothed seed (3 or more in B. tripartita and B. pilosa) also having larger flower heads.
November to April
Animal dispersed seed.
Reason for introduction
Probably a seed or soil contaminant.
Can be controlled manually, mechanically or herbicidally depending on situation.
bidens: From the Latin bi- ‘two’ and dens ‘teeth;, the seed having two tooth-like projections
Prepared by Paul Champion and Deborah Hofstra (NIWA). Features description from Webb et al., (1998).
References and further reading
Webb, C.J.; Sykes, W.R.; Garnock-Jones, P.J. (1988). Flora of New Zealand Volume 4: Naturalised pteridophytes, gymnosperms, dicotyledons. Botany Division, DSIR, Christchurch.
Popay et al (2010). An illustrated guide to common weeds of New Zealand, third edition. NZ Plant Protection Society Inc, 416pp.
Johnson PN, Brooke PA (1989). Wetland plants in New Zealand. DSIR Field Guide, DSIR Publishing, Wellington. 319pp.