Annual, usually unbranched, herb to 2 m. Stems aculeate with small, rather sparse, prickles usually pointing upwards, otherwise nearly glabrous or with a longitudinal line of crisped pubescence. Leaves: petiole up to 22 cm; lamina up to 15 × 15 cm, usually subcircular in outline, 3-7-palmately lobed, the segments usually narrowly elliptic to linear (occasionally broader), scaberulous or almost glabrous with a few minute prickles on the nerves, usually with a prominent gland on the under surface near the base of the midrib; margin serrate or dentate. Flowers up to 10 cm in diameter, white, greyish or pale yellow, with dark purple centre. Epicalyx of 7-8 bracts; each up to 18 mm, linear. Calyx up to 25 mm, setose, 10-nerved; lobes acuminate or long-acuminate; gland on midrib of calyx lobe conspicuous, usually at least 1.5 mm in diameter (rarely 0). Capsule up to 20 × 15 mm. Seeds minutely faveolate.