Description

Key Characters:

Growth Form: Annual herbs.

Stems: Stems 3–15 dm long, loosely branched above, usually hirsute toward base, the hairs simple.

Roots:

Leaves: Leaves simple. Alternate or rarely opposite. Lower blades pinnately lobed, the lobes oblong and dentate, gradually changing upward on the plant to leaves with linear to filiform, entire segments. Margins detate (lower leaves) to entire (upper leaves). Petioles1–10(–15) cm long. Stipules absent.

Flowers: Flowers usually bractless, in dense racemes elongating in fruit. Flowers bisexual (perfect), actinomorphic or rarely slightly irregular. Calyx of 4 sepals, deciduous, erect, usually oblong, sometimes the inner 2 with gibbous bases that hold the nectar, often yellow–tinged, 3.5–5 mm long. Corolla of 4 petals, pale yellow, fading white, 6–9 mm long, entire to emarginate, rarely lobed or fimbriate, usually with an elongate claw. Stamens (2–4)6(–16), tetradynamous, the inner 4 usually in pairs, sometimes connate at base in pairs; anthers dithecal, opening by longitudinal slits. Ovary superior, 2(4?)-carpellate, usually 2-celled by means of a false, but usually complete septum, rarely 1-celled, sessile or rarely stipitate; ovules 1 to numerous, borne on parietal placentas on replum margin at periphery of ovary wall, campylotropous or occasionally anatropous; style 1 or occasionally absent; stigma capitate or rarely decurrent, entire or 2-lobed.

Fruit: Capsules divided into 2 cells by the usually thin and membranous septum; elongate (at least 3 times as long as wide) and referred to as a silique; linear; terete (cylindrical); straight; 5–10 cm long; nearly equalling the pedicels in diameter; glabrous; dehiscent from the base upward; exposing the septum; sometimes fruit indehiscent or dehiscent and jointed between the seeds; ± breaking up at maturity. Seeds 1 to numerous; oblong; ca. 1 mm long; wingless; often becoming mucilaginous when wet; endosperm essentially absent.

Ploidy: 2n = 14

Habitat: Naturalized and apparently relatively uncommon in dry; disturbed sites.

Elevation Range: 15–3,050 m.