Habit and leaf form. Trees, or shrubs. Young stems cylindrical, or tetragonal. Helophytic to xerophytic. Leaves usually opposite; petiolate, or subsessile; gland-dotted, or not gland-dotted; simple. Leaf blades entire; elliptic, or ovate; pinnately veined; cross-venulate. Leaves with stipules. Stipules caducous (minute). Leaf blade margins entire. Leaves without a persistent basal meristem. Leaf anatomy. Hairs present, or absent. Stem anatomy. Secondary thickening developing from a conventional cambial ring.
Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Plants homostylous, or heterostylous. Entomophilous.
Inflorescence and flower features. Flowers solitary, or aggregated in ‘inflorescences’; paniculate in cymes. The terminal inflorescence unit cymose, or racemose. Inflorescences terminal and axillary. Flowers two bracteolate; minute to medium-sized; regular; 6 merous; partially acyclic. The androecium acyclic. Floral receptacle developing an androphore, or with neither androphore nor gynophore. Free hypanthium present; campanulate, or obconic (infundibular); ridged, angular or subulate; sinus appendages prominent or obscure. Hypogynous disk present, or absent. Perianth with distinct calyx and corolla; (3–)8–16(–32); 2 -whorled; isomerous. Calyx present, or absent; 6; 1 -whorled; gamosepalous; blunt-lobed; lobes valvate; tubular, or campanulate, or urceolate; unequal but not bilabiate, or regular; persistent. Epicalyx present, or absent. Corolla present; 6; 1 -whorled; polypetalous; plicate; unequal but not bilabiate, or regular; pink to purple. Petals oblong; clawed. Androecial members indefinite in number. Androecium 100 (‘many’). Androecial sequence determinable. Androecial members maturing centripetally; adnate (to the hypanthium, low down); all equal, or markedly unequal; free of one another; 1–3 -whorled (or several). Androecium exclusively of fertile stamens. Stamens 50–100 (many); attached inside the hypanthium; reduced in number relative to the adjacent perianth to isomerous with the perianth to polystemonous; alternisepalous, or oppositisepalous; inflexed in bud, or erect in bud. Anthers dorsifixed; versatile; dehiscing via longitudinal slits; introrse; tetrasporangiate. Gynoecium 3–6 carpelled. The pistil 3–6 celled. Gynoecium syncarpous; eu-syncarpous; superior. Ovary plurilocular; 3–6 locular; sessile. Gynoecium stylate. Styles 1; apical. Stigmas 1; capitate. Placentation axile. Ovules (1–)5–50 per locule; ascending, or horizontal; non-arillate; anatropous.
Fruit and seed features. Fruit non-fleshy; dehiscent; a capsule. Capsules loculicidal. Seeds non-endospermic; winged (the wing unilateral). Cotyledons 2. Embryo straight.
Etymology. In honour of Magnus Lagerstroem (1696–1759), a friend of Linnaeus and benefactor of Uppsala University.