Flora of New Zealand Series

black mustard

Annual herb with lax rosette. Stems erect, glabrous above, bristly below, ribbed, 0.6-1-(2) m tall. Lvs green, petiolate, sparsely bristly. Lower lvs lyrate-pinnatifid, to 16 cm long; margins dentate; terminal lobe large, 3-lobed to ovate; lateral lobes subacute, in 1-2 pairs. Upper stem lvs not lobed, becoming entire, lanceolate, 3-5 × 0.5-1 cm. Racemes to 40 cm long; buds overtopping or level with open fls. Sepals narrow-oblong, 3-4 × c. 1 mm. Petals bright yellow, 7-8 × 2-3 mm. All stamens erect. Silique quadrangular, glabrous, oblong, appressed to rachis, somewhat constricted between seeds, (6)-12-25 × 2 mm; gynophore 0; valves strongly keeled, with prominent median and weak lateral veins; beak slender, seedless, (1.5)-2-4 mm long. Seeds red-brown, c. 1 mm diam.

N.: Auckland (Waitemata Harbour); S.: Canterbury, Otago.

Europe, N. Africa, S.W. Asia 1870

A rare casual weed on waste land and among crops.

This sp. has also been referred to in N.Z. as B. sinapioides and as Sinapis nigra.