Habit and leaf form. Herbs. Annual. Leaves basal and cauline. Plants with a basal concentration of leaves, or with neither basal nor terminal concentrations of leaves. Stem internodes solid. To 0.05–0.3 m high (or prostrate). Mesophytic and xerophytic. Leaves small to medium-sized; alternate; spiral; ‘herbaceous’; petiolate (in W.A. species), or subsessile to sessile; non-sheathing; foetid, or without marked odour; simple; epulvinate. Leaf blades dissected to entire; when dissected, pinnatifid; one-veined, or pinnately veined; cross-venulate. Leaves without stipules. Leaf blade margins entire. Leaves without a persistent basal meristem. Leaf anatomy. Hairs present, or absent; glandular hairs absent; complex hairs absent. Branched hairs absent. 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, or in corymbs. The terminal inflorescence unit racemose. Flowers pedicellate; ebracteate; ebracteolate; minute to medium-sized; 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 (decussate pairs in 2 whorls); 2 -whorled; polysepalous; decussate; regular. Corolla present; 4; 1 -whorled; alternating with the calyx; polypetalous; imbricate, or contorted; regular; white, or cream, or yellow, or pink (or mauve in W.A. species). 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 (the outer pair shorter); 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; unappendaged. Pollen shed as single grains. Gynoecium 2 carpelled. The pistil 1 celled (the septum reduced or absent). Gynoecium syncarpous; eu-syncarpous; superior. Ovary unilocular to plurilocular; 1–2 locular. Locules secondarily divided by ‘false septa’ to without ‘false septa’. Gynoecium transverse. Ovary sessile. Gynoecium stylate. Styles 1; apical. Stigmas 1; commissural; 1 - lobed, or 2 - lobed; more or less capitate. Placentation parietal. Ovules in the single cavity 20–100 (many); 20–50 per locule (many); with ventral raphe; non-arillate; anatropous.
Fruit and seed features. Fruit 3–10 mm long; non-fleshy; dehiscent; a siliqua. Capsules valvular. Fruit 1 celled (the septum reduced or absent); 20–100 seeded (numerous). Seeds scantily endospermic, or non-endospermic; not mucous; small to medium sized; wingless. Embryo well differentiated. Cotyledons 2; incumbent. Embryo bent.
Physiology, biochemistry. Mustard-oils present.
Special features. Fruit body with no clear differentiation into valve and beak regions. Replum incomplete or absent. Fruit bilaterally compressed to terete. The inner (lateral) pair of sepals saccate basally for nectar storage, or not noticeably saccate. Petals not peculiarly elongated as in Stenopetalum. Nectariferous glands lateral only.
Etymology. After Carl Theodor Menke (1791–1861), German botanist and physician.