Descurainia pinnata, blue tansy mustard

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Intermountain Flora
Annual, 0.8-4 (7) dm tall, from a taproot; herbage sparsely to densely pubescent with minute branched hairs, sometimes glabrous above, eglandular, or in some stipitate-glandular above; stem simple, erect, usually branched; leaves basal and cauline, the basal withered by anthesis, the lower cauline leaves 1-10 cm long, ovate to lanceolate in outline, pinnate with pinnatifid or sometimes bipinnatifid pinnae, progressively reduced upwards and less divided with linear to filiform lobes with entire to dentate margins; racemes elongating in fruit , the rachis glabrous or sparsely stellate-pubescent or stipate-glandular; sepals 1-2 mm long, oblong, ovate, or lanceolate, erect, often scarious apically, glabrous or sometimes sparsely pubescent; petals 1.3-2.5 mm long, the blade oblanceolate, bright yellow or pale yellow to whitish, fruiting pedicels ascending, divaricately ascending, or widely spreading, (1.5) 2-15 mm long in ours; siliques ascending to erect, 4-15 mm long, 0.9-1.8 mm thick, clavate to broadly linear, acuminate to acute at the base and obtuse or rounded apically, straight to somewhat incurved, terete, the valves relatively prominently 1-nerved; mature style from obsolete to 0.15 mm long; seeds 5-20 in 2 rows in each locule or sometimes crowded into 1 row, 0.6-1.2 mm long, narrowly ellipsoid, brownish, reticulate, the cotyledons incumbent; 2n = 14, 28, 42.

Cronquist, A., Holmgren, N.H., and Holmgren, P.K. (2005) "Intermountain Flora" pg. 412, vol. 2 part B, The New York Botanical Garden New York.