Introduced annual forb to 1.3m tall. Leaves basal and alternating up the stems, to 15cm long, flat, hairy or hairless, lobed and toothed, upper leaves with toothed, occasionally entire, edges. Flowers sometimes small (less than 3mm across), yellow, with 4 petals, in groups at the tops of the stems, which elongate as the fruiting bodies mature.
Description and photo in G.M. Cunningham, WE Mulham, PL Milthorpe and J H Leigh (1981 and later printings) Plants of Western New South Wales page 333. Differences between species of Sisymbrium are detailed under Sisymbrium altissimum page 333.