Habit and leaf form. Hoary herbs. Annual to biennial. Leaves basal and cauline. Plants with a basal concentration of leaves; to 0.3–1 m high. Mesophytic and xerophytic. Leaves medium-sized; alternate; spiral; not decurrent on the stems; ‘herbaceous’; petiolate to sessile (the lower stalked, the upper sessile); sheathing to non-sheathing; simple; epulvinate. Leaf blades deeply dissected (the lower), or entire (the upper, more or less); flat; rosette and lower stem leaves pinnatifid (deeply lobed and lyrate); pinnately veined; cross-venulate. Mature leaf blades adaxially grey with dense hairs (lower leaves), to more or less glabrous (upper leaves). Leaves without stipules. Leaf blade margins coarsely dentate (lower leaves), or entire (upper leaves). Leaves without a persistent basal meristem. Vegetative anatomy. Plants without silica bodies. Leaf anatomy. Hairs present; complex hairs absent. Branched hairs absent. Stem anatomy. Nodes unilacunar, or tri-lacunar, or multilacunar. Secondary thickening developing from a conventional cambial ring, or anomalous.
Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Floral nectaries present. Nectar secretion from the disk. Entomophilous.
Inflorescence and flower features. Flowers aggregated in ‘inflorescences’; in racemes, or in corymbs. The terminal inflorescence unit racemose. Inflorescences terminal. Flowers pedicellate; ebracteate; ebracteolate; small to medium-sized; odourless; more or less regular; 2 merous; cyclic; polycyclic. Floral receptacle with neither androphore nor gynophore. Free hypanthium absent. Hypogynous disk present, or absent; of separate members, or annular. Perianth with distinct calyx and corolla; 8; 3 -whorled (K 2+2, C4); anisomerous (i.e. K in two whorls of 2, C in one whorl of 4). Calyx present; 4; 2 -whorled; polysepalous; sub- erect; decussate; regular; somewhat dimorphic, with the lateral (inner) members basally slightly saccate; persistent, or not persistent. Corolla present; 4 (diagonal); 1 -whorled; polypetalous; imbricate, or contorted; regular; plain, or with contrasting markings (often with dark veins); white, or cream, or yellow; deciduous; non-accrescent. Petals shortly clawed. Androecial members definite in number. Androecium 6. Androecial members branched (the inner whorl of 4 representing 2 primordia); free of the perianth; markedly unequal; free of one another, or coherent; 2 -whorled (2+4). Androecium exclusively of fertile stamens. Stamens 6; tetradynamous; oppositisepalous. 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; ‘falsely’ 2 locular. Locules secondarily divided by ‘false septa’ (the replum being a ‘false septum’). Gynoecium transverse. Ovary sessile. Gynoecium non-stylate, or stylate. Styles 1 (more or less reduced); attenuate from the ovary; apical. Stigmas 1–2; commissural; 1 - lobed, or 2 - lobed; more or less capitate; dry type; papillate; Group II type. Placentation parietal. Ovules 3–10 per locule (one row per cell); pendulous, or horizontal; with ventral raphe; non-arillate; anatropous.
Fruit and seed features. Fruit about 8–15 mm long; non-fleshy; dehiscent; a siliqua. Capsules valvular (the valves falling or spreading upwards to reveal the replum). Seed rows per locule 1. Seeds scantily endospermic, or non-endospermic; mucous, or not mucous; ovoid or oblong; small. Embryo well differentiated. Cotyledons 2; longitudinally folded; incumbent; conduplicate. Embryo chlorophyllous; bent. Seedling. Germination phanerocotylar, or cryptocotylar.
Physiology, biochemistry. Mustard-oils present. Aluminium accumulation not found. Photosynthetic pathway: C3.
Special features. Fruit body distinctly differentiated into valve and beak regions (the beak about half as long as the valves in the mature fruit). Beak containing seeds to seedless (0–2 seeds). Replum present and complete; narrow. Fruit terete. The inner (lateral) pair of sepals somewhat saccate basally for nectar storage. Petals not peculiarly elongated as in Stenopetalum. Nectariferous glands lateral and median. Siliquae fusiform (adpressed to the axis); not moniliform. Valves of the fruit neither winged nor keeled; conspicuously longitudinally veined (when young), or without conspicuous longitudinal veins (when mature); longitudinally 3 veined. Fruit not apically notched.
Geography, cytology, number of species. Adventive. A genus of 2 species; 1 species in Western Australia.
Etymology. After K. L. Hirschfeld of Holstein who published a book on horticulture in 1755.