Habit and leaf form. Herbs. Annual. Leaves cauline. Plants with neither basal nor terminal concentrations of leaves. Stem internodes solid. To 0.2–0.8 m high. Mesophytic. Leaves small to medium-sized; alternate; spiral; ‘herbaceous’; petiolate to sessile (all sessile or winged-petiolate); sheathing to non-sheathing; foetid, or without marked odour; simple; epulvinate. Leaf blades dissected, or dissected to entire; narrowly oblong, or ovate; when dissected, sinuate pinnatifid; one-veined, or pinnately veined; cross-venulate; auriculate at the base. Leaves without stipules. Leaf blade margins entire (or sinuate), or dentate (denticulate). Leaves without a persistent basal meristem. Leaf anatomy. Hairs present; glandular hairs absent; complex hairs present, or absent. Branched hairs present. Complex hairs when present, stellate. Extra-floral nectaries absent.
Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite.
Inflorescence and flower features. Flowers aggregated in ‘inflorescences’; in racemes (dense, elongate). The terminal inflorescence unit racemose. Flowers pedicellate; ebracteate; ebracteolate; small; regular; 2 merous; cyclic. Floral receptacle with neither androphore nor gynophore. Free hypanthium absent. Hypogynous disk present; of separate members. Perianth with distinct calyx and corolla; 8; 3 -whorled (K 2+2, C 4). Calyx present; 4; 2 -whorled; polysepalous; spreading; decussate; regular. Corolla present; 4; 1 -whorled; alternating with the calyx; polypetalous; imbricate, or contorted; regular; yellow. Petals clawed. Corolla members entire. Androecial members definite in number. Androecium 6. Androecial members branched (in that the inner whorl of 4 is derived from only 2 primordia); free of the perianth; markedly unequal; free of one another; 2 -whorled (2+4). Androecium exclusively of fertile stamens. Stamens 6; tetradynamous; all more or less similar in shape; hypogynous, on receptacle. Filaments not appendiculate. Anthers basifixed; non-versatile; dehiscing via longitudinal slits; introrse; unilocular to bilocular; tetrasporangiate; appendaged, or unappendaged. Pollen shed as single grains. Gynoecium 2 carpelled. The pistil 2 celled. Gynoecium syncarpous; eu-syncarpous; superior. Ovary plurilocular; 2 locular. Locules secondarily divided by ‘false septa’. Gynoecium transverse. Ovary sessile. Gynoecium stylate. Styles 1; apical. Stigmas 1 (or 2); commissural; 1 - lobed, or 2 - lobed; capitate. Placentation parietal. Ovules (1–)3–50 per locule; with ventral raphe; non-arillate; anatropous.
Fruit and seed features. Fruit 6–12 mm long; non-fleshy; dehiscent; a silicula. Capsules valvular. Fruit 20–100 seeded (many). Seeds 10–50 per locule (many). Seed rows per locule 2. Seeds scantily endospermic, or non-endospermic; mucous; ovoid-angular, ellipsoidal or orbicular; small to medium sized; wingless. Embryo well differentiated. Cotyledons 2; accumbent, or incumbent. Embryo bent.
Physiology, biochemistry. Mustard-oils present.
Special features. Fruit body with no clear differentiation into valve and beak regions. Replum present and complete; broad. Fruit bilaterally compressed, or terete; compressed parallel with the septum. The inner (lateral) pair of sepals not noticeably saccate. Petals not peculiarly elongated as in Stenopetalum. Nectariferous glands lateral only. Valves of the fruit winged; conspicuously longitudinally veined (below); longitudinally 1 veined.
Etymology. From the Greek for "ground" and "flax"; alluding to its being a weed which suppresses the vigor of flax crops.