Swamp beggars’ ticks
Vascular – Exotic
Dicotyledonous Herbs - Composites
Tall upright annual, up to 80 cm tall, with divided leaves, small yellow button-like flowers and characteristic flat black seeds usually with three barbed teeth easily attaching to clothing and hair.
Naturalised. South Island, West Coast from Karamea to Hokitika.
Water body margins and swamps.
Erect, glabrous or almost glabrous annual, 10-80 cm tall. Stems angled, branched above to form infl. Leaves 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 hermaphrodite;, 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.
Differs from the two other Bidens species found in New Zealand (B. frondosa, B. pilosa) by the lower simple lower cauline leaves rather than lower cauline leaves which are lobed or 1-pinnatisect; by the capitula being 4-10 mm diameter, and by the achenes which have 3-4 awns
Animal dispersed seed.
Reason for introduction
Probably a seed or soil contaminan.
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
Fact Sheet prepared by Paul Champion and Deborah Hofstra (NIWA). Description from Webb et al. (1988)
References and further reading
Clapham, A.R.; Tutin, T.G.; Warburg, E.F. 1962: Flora of the British Isles. Cambridge University Press, Second Edition. 1269pp.
Johnson P.N.; Brooke P.A. 1989: Wetland plants in New Zealand. DSIR Field Guide, DSIR Publishing, Wellington. 319pp.
Popay et al (2010). An illustrated guide to common weeds of New Zealand, third edition. NZ Plant Protection Society Inc, 416pp.