Common name. Shepherds Purses. Family Brassicaceae.
Habit and leaf form. Herbs. Annual, or biennial. Leaves basal and cauline. Plants with a basal concentration of leaves. Stem internodes solid. To 0.08–0.4 m high. Mesophytic, or xerophytic. Leaves small to medium-sized; alternate; spiral; ‘herbaceous’; petiolate (basal leaves), or subsessile to sessile (cauline leaves); sheathing to non-sheathing; without marked odour; simple; epulvinate. Leaf blades dissected, or entire; when dissected, lobed or lyrate pinnatifid; pinnately veined; cross-venulate; auriculate at the base (basal leaves). Leaves without stipules. Leaf blade margins entire, or serrate, or dentate. Leaves without a persistent basal meristem. Leaf anatomy. Hairs present; glandular hairs absent; complex hairs present. Branched hairs present, or absent. Complex hairs 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 (slender, erect). The terminal inflorescence unit racemose. Flowers pedicellate; ebracteate; ebracteolate; minute to small; regular; 2 merous; cyclic. Floral receptacle with neither androphore nor gynophore. Free hypanthium absent. Hypogynous disk present; of separate members. Nectariferous glands 4. Perianth with distinct calyx and corolla; 4 (rarely), or 8; 3 -whorled (usually, K 2+2, C 4), or 2 -whorled. Calyx present; 4; 2 -whorled; polysepalous; erect; decussate; regular. Corolla present, or absent (rarely); when present, 4; 1 -whorled; alternating with the calyx; polypetalous; imbricate, or contorted; regular; white. Petals obovate (or narrow); when present, clawed. 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 (2 outer, 4 inner); tetradynamous; all more or less similar in shape; hypogynous, on receptacle, outer stamens lateral. 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; 1 - lobed (capitate); capitate. Placentation parietal. Ovules 3–10 per locule (several); with ventral raphe; non-arillate; anatropous.
Fruit and seed features. Fruit 6–9 mm long; non-fleshy; dehiscent; a silicula. Capsules valvular. Fruit 2 celled; 10–30 seeded. Seeds 5–15 per locule. Seed rows per locule 2. Seeds scantily endospermic, or non-endospermic; not mucous; compressed; small to medium sized; wingless. Embryo well differentiated. Cotyledons 2; flat; accumbent (rarely), 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; narrow. Fruit bilaterally compressed (usually obcordate); compressed at right angles to 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 keeled. Fruit apically notched.
Etymology. From the Latin for "box, satchel" and the diminutive -ell-; refers to the compressed pod.