Common name. Cestrums. Family Solanaceae.
Habit and leaf form. Shrubs; resinous, or not resinous. Stem internodes solid. Helophytic to xerophytic. Leaves alternate (usually), or alternate to opposite; usually spiral (at least below); ‘herbaceous’, or leathery; petiolate; non-sheathing; not gland-dotted; simple; epulvinate. Leaf blades entire; narrowly elliptic to ovate; pinnately veined; cross-venulate. Leaves without stipules; without a persistent basal meristem. Leaf anatomy. Hairs present (new shoots and leaf axils minutely pubescent); glandular hairs absent, or present. Extra-floral nectaries absent.
Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Entomophilous.
Inflorescence and flower features. Flowers aggregated in ‘inflorescences’; in panicles (or panicle-like). The terminal inflorescence unit cymose. Inflorescences terminal; inflorescence compact and congested with numerous flowers. Flowers pedicellate (articulated), or sessile; bracteate (occasionally), or ebracteate; ebracteolate; small to medium-sized; fragrant (corolla sweet scented in West Australian species), or odourless; regular, or somewhat irregular (sometimes slightly). The floral asymmetry when noticeable) involving the androecium. Flowers mostly 5 merous; cyclic; tetracyclic. Free hypanthium absent. Hypogynous disk present. Perianth with distinct calyx and corolla; 10(–14); 2 -whorled; isomerous. Calyx present; 5 (–7); 1 -whorled; gamosepalous; blunt-lobed; tubular; unequal but not bilabiate, or regular; persistent; non-accrescent. Calyx lobes triangular. Corolla present; 5 (–7?); 1 -whorled; gamopetalous. Corolla lobes markedly shorter than the tube. Corolla valvate; tubular (narrow); regular; green, or yellow (greenish yellow). Androecial members definite in number. Androecium 5 (–7?). Androecial members adnate; all equal, or markedly unequal; free of one another; 1 -whorled. Androecium exclusively of fertile stamens. Stamens 5 (–7?). Staminal insertion midway down the corolla tube. Stamens all inserted at the same level; remaining included; not didynamous, not tetradynamous; all more or less similar in shape; isomerous with the perianth; oppositisepalous (near the middle of the corolla tube). Filaments appendiculate, or not appendiculate; glabrous. Anthers separate from one another; dorsifixed, or basifixed; versatile; dehiscing via longitudinal slits; introrse; tetrasporangiate. Pollen shed in aggregates, or shed as single grains. Gynoecium 2 carpelled. The pistil 2 celled. Gynoecium syncarpous; synstylovarious to eu-syncarpous; superior. Ovary plurilocular; 2 locular. Gynoecium oblique. Ovary on a prominent disc. Gynoecium stylate. Styles 1; attenuate from the ovary; apical. Stigmas 1; 1 - lobed, or 2 - lobed (L); capitate (AP). Placentation axile. Ovules 10–50 per locule (numerous, few); non-arillate; anatropous, or hemianatropous.
Fruit and seed features. Fruit fleshy; not spinose; indehiscent; a berry; 20–100 seeded (numerous). Seeds endospermic. Endosperm oily, or not oily. Cotyledons 2. Embryo straight, or straight to curved.
Special features. Corolla tube exceeding the calyx.
Etymology. Name variously said to derive from the Greek for "a plant", or "an engraver's tool"; in reference to the anther shape, or because of the supposed similarity to a plant of the same name described by Dioscorides.