Ludwigia L.

Scientific Description

Family Onagraceae.

Habit and leaf form. Shrubs, or herbs; bearing essential oils, or without essential oils. Herbs annual, or perennial; plants with a basal concentration of leaves, or with neither basal nor terminal concentrations of leaves. Often hydrophytic, or helophytic; when hydrophytic, rooted. Leaves when hydrophytic, emergent and floating; alternate, or opposite, or whorled (rarely); when alternate, spiral; petiolate, or subsessile; non-sheathing; simple; epulvinate. Leaf blades dissected, or entire (usually); usually elliptic, or oblong, or ovate; when dissected, i.e. rarely, pinnatifid; pinnately veined; cross-venulate. Leaves with stipules (reduced), or without stipules. Stipules when present, intrapetiolar; free of one another; caducous. Leaves without a persistent basal meristem. Leaf anatomy. Hairs present. Roots. Aerial roots present, or absent.

Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Anemophilous, or entomophilous.

Inflorescence and flower features. Flowers usually solitary, or aggregated in ‘inflorescences’. Inflorescences axillary; flowers usually solitary, occasionally clustered in upper leaf axils or in an inflorescence. Flowers pedicellate; often bracteolate, or ebracteolate; small to large; regular; 4–5 merous; cyclic; tricyclic, or tetracyclic, or pentacyclic. Free hypanthium present; not extending beyond ovary. Perianth with distinct calyx and corolla; 4–8(–14); 2 -whorled; isomerous. Calyx present; 3–7; 1 -whorled; polysepalous; lobes valvate; persistent. Sepals elliptic, or ovate, or obovate, or triangular. Corolla present, or absent; (3–)4–5(–7); 1 -whorled; polypetalous; imbricate, or contorted; white, or cream, or yellow. Petals clawed, or sessile. Androecial members definite in number. Androecium 4–5, or 8, or 10. Androecial members adnate (to the hypanthium), or free of the perianth (on the disk); all equal, or markedly unequal; free of one another; 2 -whorled (often), or 1 -whorled. Androecium exclusively of fertile stamens. Stamens 4, or 5, or 8, or 10; isomerous with the perianth, or diplostemonous. Anthers dorsifixed, or basifixed (apparently, by reduction); versatile; dehiscing via longitudinal slits; introrse; tetrasporangiate. Pollen shed in aggregates, or shed as single grains; with viscin strands, or without viscin strands; if in aggregates, in tetrads. Gynoecium (3–)4(–7) carpelled. The pistil 3–7 celled. Carpels isomerous with the perianth. Gynoecium syncarpous; synstylovarious, or eu-syncarpous; inferior. Ovary plurilocular; 3–7 locular. Epigynous disk present. Gynoecium stylate. Styles 1; apical. Stigmas 1–4. Placentation axile, or parietal. Ovules 1–50 per locule (to ‘many’); pendulous, or ascending; non-arillate; anatropous.

Fruit and seed features. Fruit fleshy, or non-fleshy; dehiscent, or indehiscent; a capsule, or capsular-indehiscent. Capsules splitting irregularly, or loculicidal (by 4–10 valves). Fruit 2–100 seeded (‘many’). Seeds non-endospermic; not conspicuously hairy. Cotyledons 2. Embryo straight.

Etymology. After Christian Gottlieb Ludwig (1709–73), botanist and professor of medicine at Leipzig.