Habit and leaf form. Herbs. Plants unarmed. Annual. Leaves cauline. Plants with neither basal nor terminal concentrations of leaves; to 0.2–0.4 m high. Mesophytic. Leaves small to medium-sized; alternate; spiral; not decurrent on the stems; ‘herbaceous’, or fleshy; not imbricate; petiolate. Petioles wingless. Leaves non-sheathing; simple; epulvinate. Leaf blades deeply dissected; flat, or folded; pinnatifid, or much-divided (pinnati- or bipinnatisect); pinnately veined. Mature leaf blades glabrous; adaxially glabrous. Leaves without stipules. Leaf anatomy. Hairs present, or absent; glandular hairs absent; complex hairs absent. Branched hairs absent.
Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Floral nectaries present.
Inflorescence and flower features. Flowers aggregated in ‘inflorescences’; not in pairs subtended by a common bract; in racemes. Inflorescences simple. The terminal inflorescence unit racemose. Inflorescences terminal; ascending. Flowers pedicellate; ebracteate; ebracteolate; small; regular; 2 merous. Floral receptacle with neither androphore nor gynophore. Free hypanthium absent. Hypogynous disk present. Perianth with distinct calyx and corolla; 8; 3 -whorled; isomerous. Calyx present; 4; 2 -whorled; polysepalous; erect; decussate; exceeded by the corolla; non-fleshy; non-accrescent. Corolla present; 4; 1 -whorled; polypetalous; imbricate, or contorted; regular; yellow; non-accrescent. Petals clawed. Androecium present. Fertile stamens present. Androecial members definite in number. Androecium 6. Androecial members branched; free of the perianth; markedly unequal; free of one another; 2 -whorled. Androecium exclusively of fertile stamens. Stamens 6; tetradynamous; oppositisepalous; filantherous. Filaments not appendiculate. Anthers basifixed; non-versatile; dehiscing via longitudinal slits; introrse; unilocular, or bilocular; tetrasporangiate; unappendaged. Gynoecium 2 carpelled. The pistil 2 celled. Gynoecium syncarpous; eu-syncarpous; superior. Ovary plurilocular; 2 locular. Locules secondarily divided by ‘false septa’. Gynoecium transverse; stylate. Styles 1; simple; apical; persistent. Stigmas 1; commissural. Placentation parietal. Ovules 1 per locule.
Fruit and seed features. Fruit aerial; about 20 mm long; non-fleshy; spinose; dehiscent; a silicula. Capsules valvular. Fruit 2 celled. Dispersal unit the seed. Fruit 2 seeded. Seeds 1 per locule. Seeds not compressed (globose). Cotyledons 2; folded; conduplicate.
Physiology, biochemistry. Mustard-oils present.
Special features. Fruit body distinctly differentiated into valve and beak regions. Beak seedless. Replum present and complete; broad. Petals not peculiarly elongated as in Stenopetalum. Nectariferous glands lateral and median. Fruit not apically notched.
Geography, cytology, number of species. Holarctic. World distribution: Mediterranean. Adventive. Australian states and territories: Western Australia. 1 species in Western Australia; S. balearica (L.) Medicus.