Lepidium L.

Scientific Description

Common name. Peppercresses. Family Brassicaceae.

Habit and leaf form. Shrubs, or herbs. Annual, or biennial. Leaves cauline. Stem internodes solid. To 0.1–2 m high. Mesophytic to xerophytic. Leaves small to medium-sized; alternate; spiral; ‘herbaceous’, or fleshy (rarely); petiolate, or subsessile, or sessile; non-sheathing; foetid, or without marked odour; simple; epulvinate. Leaf blades entire; linear, or obovate (or narrowly so, sometimes subterete); one-veined, or pinnately veined; cross-venulate. Leaves without stipules. Leaf blade margins entire, or serrate, or dentate. 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’; elongated in racemes (usually), or in corymbs. The terminal inflorescence unit racemose. Inflorescences terminal. Flowers pedicellate; ebracteate; ebracteolate; minute to small; regular to somewhat irregular; 2 merous; cyclic; tetracyclic, or pentacyclic, or polycyclic. Floral receptacle developing a gynophore, or with neither androphore nor gynophore. Free hypanthium absent. Hypogynous disk present; of separate members. Nectariferous glands 6, or 4. Perianth with distinct calyx and corolla, or sepaline; 4, or 8; 2 -whorled, or 3 -whorled. Calyx present; 4; 2 -whorled; polysepalous; decussate; regular. Corolla present, or vestigial to absent (sometimes); when present, 4; 1 -whorled; alternating with the calyx; polypetalous; imbricate, or contorted; regular; white. Petals clawed. Corolla members entire. Androecial members definite in number. Androecium 2, or 4, or 6. Androecial members branched (in that the inner whorl of 4 is derived from only 2 primordia), or unbranched (when only 2 stamens); free of the perianth; all equal, or markedly unequal; free of one another, or coherent (the inner four basally connate in pairs); 1 -whorled, or 2 -whorled (2+4). Androecium exclusively of fertile stamens. Stamens 2, or 4, or 6; tetradynamous, or not didynamous, not 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; 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 (usually), or stipitate (rarely). Gynoecium non-stylate, or stylate. Styles 1; apical. Stigmas 1; commissural; slightly 2 - lobed, or 1 - lobed; capitate. Placentation parietal. Ovules (1–)3–50 per locule; with ventral raphe; non-arillate; anatropous.

Fruit and seed features. Fruit non-fleshy; dehiscent; a silicula. Capsules valvular. Fruit 2 seeded. Seeds usually 1 per locule. Seeds scantily endospermic, or non-endospermic; mucous; compressed, or not compressed (‘round’ to flat); small to medium sized; winged, or wingless. Embryo well differentiated. Cotyledons 2; folded (or ‘simple or divided’); accumbent (rarely), or incumbent; if folded, diplecolobous. 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; 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 (usually), or lateral and median (then medians fused with the laterals). Valves of the fruit keeled to winged. Fruit apically notched (usually), or not apically notched.

Etymology. From the Latin lepidium, name used by Pliny for L. latifolium, probably from the Greek for "scale"; in reference to the pods.