Microlepidium F.Muell.

Scientific Description

Family Brassicaceae.

Habit and leaf form. Herbs. Annual. Leaves basal and cauline. Stem internodes solid. To 0.1–0.2 m high. Mesophytic, or xerophytic. Leaves small; alternate; spiral; ‘herbaceous’; petiolate to sessile; non-sheathing; foetid, or without marked odour; simple; epulvinate. Leaf blades entire; basal and cauline leaves obovate; one-veined, or pinnately veined. Leaves without stipules. Leaf blade margins entire, or dentate (the basal leaves remotely dentate to entire, the cauline coarsely dentate to entire). Leaves without a persistent basal meristem. Leaf anatomy. Hairs present; glandular hairs absent; complex hairs present. Branched hairs present. 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 corymbs, or in racemes (elongating from a corymb). The terminal inflorescence unit racemose. Inflorescences dense. Flowers pedicellate; ebracteate; ebracteolate; minute; regular; 2 merous; cyclic. Floral receptacle with neither androphore nor gynophore. Free hypanthium absent. Hypogynous disk present; of separate members. Nectariferous glands 2, or 4, or 6. Perianth with distinct calyx and corolla, or sepaline (corolla sometimes lacking); 8, or 4; 3 -whorled (K 2+2, C 4), or 2 -whorled. Calyx present; 4; 2 -whorled; polysepalous; decussate; regular. Corolla present to vestigial; when present, 4; 1 -whorled; alternating with the calyx; polypetalous; imbricate, or contorted; regular; white, or yellow, or orange, or purple, or blue. Petals clawed. Corolla members emarginate or 3-lobed. 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; tetradynamous; all more or less similar in shape; hypogynous, on receptacle. Filaments appendiculate, or 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 non-stylate, or stylate (sessile or almost so). Styles 1; apical. Stigmas 1 (or 2); commissural; 1–2 - lobed (capitate or obscurely bilobed); capitate. Placentation parietal. Ovules 3–10 per locule (several); with ventral raphe; non-arillate; anatropous.

Fruit and seed features. Fruit 3–5.5 mm long; non-fleshy; dehiscent; a silicula. Capsules valvular. Fruit 2 celled; 4–18 seeded. Seeds 2–9 per locule. Seeds scantily endospermic, or non-endospermic; mucous; ellipsoidal; small to medium sized; winged. 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 present and complete; narrow. Fruit bilaterally compressed to terete; compressed at right angles to the septum. Petals not peculiarly elongated as in Stenopetalum. Nectariferous glands lateral and median, or lateral only. Valves of the fruit winged. Fruit apically notched.

Etymology. From the Greek for "small" and Lepidium; refers to the similarity to Lepidium within the Brassicaceae.