Latin bis — twice, dens — tooth, as the pappus often consists of two sharp, tooth-like bristles.
Mostly annual or perennial herbs, rarely shrubs. Stems procumbent, erect or ascending. Leaves along stems, mostly opposite, rarely whorled, entire, lobed or variously divided. Capitula radiate or diskoid, terminal, solitary or in corymbs or panicles, long-stalked; mostly summer. Involucral bracts in 2 rows, overlapping, unequal, outer leaf-like, inner with membranous margins. Receptacle with scales, pitted, flat to conical. Ray florets female or sterile, usually yellow. Disk florets usually bisexual, yellow or brownish. Achenes angled or compressed, sometimes winged. Pappus of 2-4 short, barbed bristles, sometimes absent.
Five species have become minor weeds in Australia, usually in moist disturbed areas. A few species have some horticultural value.
The following species have radiate capitula: B. bipinnata L. from S America, an almost glabrous annual herb to 1.5 m tall, with deeply divided leaves, small capitula (to about 1 cm across) and yellow ray florets; B. ferulifolia (Jacq.) DC. from N America, an almost glabrous annual or perennial herb to 1 m tall with deeply divided leaves, rather large capitula (to about 3 cm across) and golden yellow ray florets; B. pilosa L. from S America, an almost glabrous to densely hairy annual herb to 1m tall, which has usually 3-lobed leaves with toothed leaflets, small capitula (to about 1.5 cm across) and white ray florets; and B. subalternans DC. from S America, an almost glabrous annual herb to 1.5 m tall, with deeply divided leaves, small capitula (to about 1 cm across) and yellow ray florets.
Pappus of a few short, barbed bristles.
About 240 species, virtually cosmopolitan but mostly in N and S America.
Sherff (1937), Tadesse (1984).
Source: (2002). Asteraceae. In: . Horticultural Flora of South-eastern Australia. Volume 4. Flowering plants. Dicotyledons. Part 3. The identification of garden and cultivated plants. University of New South Wales Press.