Thlaspi arvense, pennycress

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Intermountain Flora
Annual or winter annual, 1.5-5 dm tall, from a taproot; herbage glabrous; stem erect, single, simple, or usually branched throughout; leaves basal and cauline, the basal ones not truly rosulate, early deciduous, the lower cauline leaves 2.5-4.5 (6) cm long, 0.5-1.5 cm wide, oblanceolate, irregularly dentate to sinuate, obtuse to rounded apically, the lowermost tapering into a winged petiole, the middle and upper ones sessile, sagittate-clasping; racemes elongating in fruit; sepals 1.4-2.5 mm long, oblong, broadly rounded; petals (2) 2.5-3.7 mm long, spatulate, white; anthers about 0.3 mm long; fruiting pedicels 7-13 mm long, slender, divaricately ascending; silicles erect, 10-15 mm long, 9-13 mm wide, broadly oboviod to suborbicular, apically emarginate with a deep, narrow u-shaped sinus, strongly flattened with wide wings, the body 7.5-10 mm long, 5.2-5.8 mm wide, oboviod; mature style short, 0.1-0.3 mm long, persistent, the stigma small, capitata; seeds 5-7 per locule, 1.7-2.2 mm long, broadly oval, with distinct circular ridges converging on the funicular attachment, dark reddish-brown, the cotyledons accumbent; 2n = 14.

Cronquist, A., Holmgren, N.H., and Holmgren, P.K. (2005) "Intermountain Flora" pg. 268-289, vol. 2 part B, The New York Botanical Garden New York.