Bidens tripartitaBidens tripartitaTaxonomy
Bidens tripartita L., Sp. Pl. 2:831. 1753Common name
Erect / trifid burr marigold, three lobe / three part beggarticks
Description
Propagule or dispersal unit is the fruit with pappus. Fertile part (4-)5.5-9 mm long, 1.5-2.6 mm wide, in side view widest in upper part (obovoid), +/- straight, the upper (apical) end suddenly cut off (truncate), in cross-section flattened, basal scar (carpopodium) inconspicuous and undifferentiated, central, beak (=thinner sterile stalk between seed and pappus) absent, wings absent, fruit surface dark brown or reddish to pink, smooth (except at cellular level), with no hairs (glabrous), thickened margin absent, longitudinal ribs present, 3-5, their surfaces smooth or toothed, serrated or scale-like, with no hairs (glabrous) or simple straight hairs.
Pappus type awns or spines, pappus elements all +/- similar, rarely clearly differentiated, up to 3-4 mm long, in one row, number of pappus elements two, rarely three to four, persistent, the individual awns serrated or barbed, +/- upright, +/- straight.
Note: Bidens tripartita is the most distinctive of the Bidens covered in this key because of its flattened fruits.
Ecology
Annual herb, seeds dispersed by sticking to fur or clothes. Temperate regions. Found on rich soils, often in moist to wet conditions such as near water bodies and in wet pastures.
Native range
Across the northern hemisphere, i.e. southern Canada, United States, most of Europe, Algeria, Asia from Caucasus to China, Japan, Taiwan
Introduced range
South-eastern Australia, New Zealand, Pacific Islands
