Coronopus Zinn

Scientific Description

Common name. Swinecress. Family Brassicaceae.

Habit and leaf form. Herbs. Annual, or perennial. Leaves basal and cauline. To 0.1–0.3 m high. Mesophytic and xerophytic. Leaves medium-sized; alternate; spiral; ‘herbaceous’; petiolate (basal leaves), or subsessile to sessile (cauline leaves reducing to sessile); non-sheathing; aromatic, or without marked odour, or foetid; simple; epulvinate. Leaf blades dissected (basal, with 3–5 pairs of pinnatifid lobes), or entire (cauline, reducing to entire); when dissected, lobed pinnatifid; 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, or present; 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. The terminal inflorescence unit racemose. Inflorescences terminal and leaf-opposed (or in the forks of branches); exceeding leaves. Flowers pedicellate; ebracteate; ebracteolate; minute to small; more or less regular, or somewhat irregular; 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, or sepaline; 8, or 4; 2 -whorled, or 3 -whorled. Calyx present; 4; 2 -whorled; polysepalous; erect to spreading (‘half spreading’); decussate; regular. Corolla present to absent; if present, 4 (small); 1 -whorled; alternating with the calyx; polypetalous; imbricate, or contorted; regular; white. Petals if present, clawed, or sessile. 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 (the outer pair shorter); free of one another; 2 -whorled (2+4), or 1 -whorled. 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. Filaments appendiculate, or 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, or stipitate. Gynoecium non-stylate, or stylate. Styles 1; apical. Stigmas 1 (or 2); commissural; 1–2 - lobed; more or less capitate. Placentation parietal. Ovules (1–)3–50 per locule; with ventral raphe; non-arillate; anatropous.

Fruit and seed features. Fruit 0.8–3 mm long; non-fleshy; dehiscent, or a schizocarp. Mericarps when schizocarpic, 2 (these 1–seeded). Fruit a silicula; 2 celled; 2(–4) seeded. Seeds 1(–2) per locule. Seeds scantily endospermic, or non-endospermic; not mucous; small to medium sized. Embryo well differentiated. Cotyledons 2; folded; incumbent; spirolobous. 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 if present, lateral only. Valves of the fruit neither winged nor keeled. Fruit apically notched.

Etymology. From the Greek for "crow" and "foot", on account of the shape of the leaves.