Common name. Evening Primroses. Family Onagraceae.
Habit and leaf form. Herbs; bearing essential oils, or without essential oils. Annual, or biennial, or perennial. Leaves basal, or cauline. Plants with a basal concentration of leaves, or with neither basal nor terminal concentrations of leaves. Mesophytic. Leaves alternate; spiral; petiolate, or subsessile; non-sheathing; simple; epulvinate. Leaf blades dissected, or entire; elliptic, or oblong, or ovate, or obovate, or linear; when dissected, pinnatifid; pinnately veined; cross-venulate. Leaves without stipules. Leaf blade margins entire, or dentate. Leaves without a persistent basal meristem. Leaf anatomy. Hairs present, or absent; glandular hairs absent, or present.
Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Anemophilous, or entomophilous.
Inflorescence and flower features. Flowers solitary, or aggregated in ‘inflorescences’; in racemes, or in spikes. Inflorescences terminal, or axillary; inflorescence spicate or racemose or flowers solitary in axils of upper leaves. Flowers small to large; regular; 4 merous; cyclic; tricyclic, or tetracyclic, or pentacyclic. Free hypanthium present; extending beyond ovary; usually much elongated, slender, deciduous above the ovary after anthesis. Perianth with distinct calyx and corolla; 8; 2 -whorled; isomerous. Calyx present; 4; 1 -whorled; partially gamosepalous (connate in pairs at tips), or gamosepalous; blunt-lobed; lobes valvate; not persistent. Corolla present; 4; 1 -whorled; polypetalous; imbricate, or contorted; white, or yellow, or orange, or red, or pink, or purple. Petals clawed, or sessile. Androecium 4–8. Androecial members adnate, or free of the perianth; all equal, or markedly unequal (inner shorter than outer whorl); free of one another; 2 -whorled, or 1 -whorled. Androecium exclusively of fertile stamens. Stamens (4–)8 (in 2 whorls); all more or less similar in shape; reduced in number relative to the adjacent perianth, or 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 1–4; usually 4 - lobed; sometimes 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 and valvular (splitting into 4 valves). Fruit 20–100 seeded (many). Seeds non-endospermic; not conspicuously hairy. Cotyledons 2. Embryo straight.
Etymology. From the Greek oinothera; name of a plant which was used to flavour wine; and the Latin oenothera; name of a plant which when its juice was added to wine, induced sleep.
Wheeler, Judy; Marchant, Neville; Lewington, Margaret; Graham, Lorraine (2002). Flora of the south west, Bunbury, Augusta, Denmark. Volume 2, dicotyledons. Australian Biological Resources Study. Canberra.
Australia. Bureau of Flora and Fauna (1990). Flora of Australia. Volume 18, Podostemaceae to Combretaceae. Australian Govt. Pub. Service. Canberra.
Marchant, N. G.; Wheeler, J. R.; Rye, B. L.; Bennett, E. M.; Lander, N. S.; Macfarlane, T. D.; Western Australian Herbarium (1987). Flora of the Perth region. Part one. Western Australian Herbarium. Perth.
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