Sisymbrium altissimum, Jim Hill mustard

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Intermountain Flora
Annual, 2-7.5 (14) dm tall, from a taproot; herbage coarsely hispid-hirsute below with simple hairs, usually glabrous above; stem usually single, erect, stout, divaricately branched, often maturing into a rounded tumbleweed; leaves petiolate, the lower leaves 1-20 cm long (measurement includes the petiole), lanceolate or oblong in outline, runcinate to pinnatifid, the lobes oblong and dentate, gradually changing upwards into deeply pinnately divided leaves with narrowly linear to filiform segments; racemes dense in flower, elongating in fruit; sepals 3-5.5 mm long, lanceolate or narrowly oblong, the outer segments with a short horn at the apex, glabrous; petals 5.5-8.5 mm long, the blade oblanceolate, pale yellow, fading to whitish; anthers about 1.4 mm long; fruiting pedicels 5-10 mm long, divaricately ascending, stout, about as thick as the mature siliques; siliques divaricately ascending to erect, 5.5-8.5 cm long, 0.9-1.3 mm thick, narrowly linear, terete, rigid, the valves 3-nerved, the septum deeply convoluted around the seeds; stigma subsessile, bifid; seeds numerous and pakced into 1 row in each locule, surrounded by the convoluted septum, each seed 0.8-1.1 mm long, oblong, flattened, cream to yellow, slightly mucilaginous when wet, the cotyledons obliquely incumbent; 2n = 14.

Cronquist, A., Holmgren, N.H., and Holmgren, P.K. (2005) "Intermountain Flora" pg. 402, vol. 2 part B, The New York Botanical Garden New York.