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1 Leaves all basal; petals deeply bifid (about 1/2 way to base)
..2 Silique twisted; petals 5-6 mm long; styles conspicuous, 1.5-3 mm long; perennial from a caudex; flowers all chasmogamous, with anthers 0.5-0.6 mm long, and with petals; [on calcareous rock outcrops]
..2 Silique not twisted; petals 0-5 mm long; styles absent to inconspicuous, 0-0.25 mm long; winter-annuals; flowers of two types, the early ones chasmogamous, with anthers 0.2-0.4 mm long, and with petals, the later ones cleistogamous, with anthers ca. 0.05 mm long, and lacking petals; [mostly in open situations in sandy or clayey soils, sometimes on rocks, including limestone].
....3 Silique 1-6 mm long; leaves extending upward into the lower branches of the inflorescence; trichomes exclusively cruciform
....3 Silique 8-14 mm long; leaves low-cauline, not extending upward into the lower branches of the inflorescence; trichomes of 2 types, simple and 2-7-rayed