Common name. Willow Herb. Family Onagraceae.
Habit and leaf form. Herbs; bearing essential oils, or without essential oils. Annual, or perennial; plants with a basal concentration of leaves, or with neither basal nor terminal concentrations of leaves. Hydrophytic, or helophytic, or mesophytic. Leaves alternate, or opposite; when alternate, spiral; petiolate to sessile; non-sheathing; simple; epulvinate. Leaf blades entire; elliptic, or ovate, or linear; pinnately veined; cross-venulate. Leaves with stipules, or without stipules. Stipules when present, intrapetiolar; free of one another; caducous. Leaf blade margins serrate, or dentate. Leaves without a persistent basal meristem.
Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Anemophilous, or entomophilous.
Inflorescence and flower features. Flowers solitary; axillary; pedicellate; ebracteolate; small to large; usually regular; 4 merous; cyclic; tricyclic, or tetracyclic, or pentacyclic. Free hypanthium present, or absent; not extending beyond ovary; short but evident if present. Perianth with distinct calyx and corolla; 8; 2 -whorled; isomerous. Calyx present; 4; 1 -whorled; gamosepalous; blunt-lobed; lobes valvate; not persistent. Corolla present; 4; 1 -whorled; polypetalous; imbricate, or contorted; white, or yellow, or red, or pink, or purple. Petals clawed, or sessile. Androecial members definite in number. Androecium 8. Androecial members adnate, or free of the perianth; markedly unequal (the alternisepalous whorl shorter); free of one another; 2 -whorled. Androecium exclusively of fertile stamens. Stamens 8 (in 2 whorls); isomerous with the perianth; alternisepalous and oppositisepalous. Anthers dorsifixed; 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 4 carpelled. The pistil 4 celled. Carpels isomerous with the perianth. Gynoecium syncarpous; synstylovarious, or eu-syncarpous; inferior. Ovary plurilocular; 4 locular. Epigynous disk present. Gynoecium stylate. Styles 1; apical. Stigmas 1; 1 - lobed, or 4 - lobed; clavate, or capitate. 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; a capsule. Capsules loculicidal, or septicidal. Fruit 2–100 seeded. Seeds non-endospermic; conspicuously hairy, or not conspicuously hairy; with a tuft of hairs, or without a tuft of hairs. Cotyledons 2. Embryo straight.
Etymology. From the Greek for "upon" and "pod"; the petals rest on the pod-like ovary.