Melastomataceae Juss.

Scientific Description

Common name. Melastome Family.

Habit and leaf form. Herbs, or herbaceous climbers, or shrubs, or trees, or lianas. Young stems often tetragonal. Self supporting, or epiphytic, or climbing; the climbers usually root climbers. Hydrophytic, helophytic, and mesophytic; when hydrophytic, rooted. Leaves whorled (rarely), or opposite (and decussate, one of each pair in some tribes commonly larger than the other, the smaller then sometimes withering early); sometimes somewhat turgescent; petiolate; simple. Leaf blades entire; lanceolate, or oblong, or ovate; palmately veined and parallel-veined (no dominant midrib, the several strong veins diverging at the base, converging at the apex); cross-venulate. Leaves without stipules. Leaf blade margins entire, or serrate. Leaves without a persistent basal meristem. Domatia recorded (about 10 genera); represented by pits, or pockets. Stem anatomy. Nodes unilacunar. Secondary thickening absent, or developing from a conventional cambial ring, or anomalous; from a single cambial ring.

Reproductive type, pollination. Fertile flowers hermaphrodite, or functionally male. Unisexual flowers present, or absent. Plants hermaphrodite, or androdioecious (some Astronieae). Floral nectaries present (in about a dozen genera), or absent. Nectar secretion from the perianth, or from the androecium. Entomophilous, or ornithophilous, or cheiropterophilous.

Inflorescence and flower features. Flowers solitary (rarely), or aggregated in ‘inflorescences’. The terminal inflorescence unit cymose. Inflorescences in great variety, usually panicled or contracted cymes. Flowers often bracteolate (the bracteoles often brightly coloured); operculate (calyptrate), or not operculate; regular, or somewhat irregular. The floral asymmetry involving the androecium. Flowers 3–5(–7) merous; cyclic. Free hypanthium present (tubular or campanulate). Perianth with distinct calyx and corolla; 8–10(–14); 2 -whorled; isomerous. Calyx 4, or 5(–7); 1 -whorled; gamosepalous (the lobes variously a mere rim on the hypanthium, sometimes united and forming a calyptra); entire, or lobed; when not entire, lobulate, or blunt-lobed, or toothed; calyptrate, or not calyptrate; imbricate, or valvate, or contorted, or open in bud; regular. Corolla 4, or 5(–7); 1 -whorled; usually polypetalous; contorted; regular. Androecium 4–5, or 8, or 10(–96) (usually twice C). Androecial members free of the perianth; all equal, or markedly unequal (often with the filaments twisted, bringing all the anthers to one side of the flower); free of one another; 1 -whorled (standing so even when ‘both whorls’ present), or 2 -whorled. Androecium exclusively of fertile stamens (often dimorphic), or including staminodes. Staminodes 4, or 5 (often alternating with the fertile members). Stamens 4–5, or 8, or 10(–96); isomerous with the perianth to diplostemonous to polystemonous; inflexed in bud; filantherous (often geniculate at the base of the connective). Anthers basifixed; non-versatile; usually dehiscing via pores (apically, with one, two or rarely four pores per anther), or dehiscing via short slits, or dehiscing via longitudinal slits; initially tetrasporangiate; often appendaged (basally, from an extension of the connective or with dorsal connective spurs), or unappendaged. Fertile gynoecium present, or absent (from male flowers). Gynoecium (3–)4–5(–14) carpelled. The pistil 1 celled, or (3–)4–5(–14) celled. Gynoecium syncarpous; eu-syncarpous; superior to inferior (the hypanthium variously quite free, or adhering to the ovary completely or only by its longitudinal nerves). Ovary unilocular, or plurilocular; (3–)4–5(–14) locular, or 1 locular (locule number usually equalling G, but sometimes unilocular through partitions failing to develop). Epigynous disk absent. Gynoecium stylate. Styles 1; apical. Stigmas 1; wet type; papillate; Group III type. Placentation when unilocular, median parietal; usually axile. Ovules (2–)6–50 per locule (usually ‘many’); anatropous (usually), or orthotropous (Rhexia).

Fruit and seed features. Fruit fleshy, or non-fleshy; dehiscent, or indehiscent; a capsule, or a berry. Capsules loculicidal. Fruit 20–100 seeded (i.e. ‘many seeded’). Seeds non-endospermic; small. Embryo well differentiated (but minute). Cotyledons 2 (often unequal). Embryo achlorophyllous (1/1). Micropyle zigzag. Seedling. Germination phanerocotylar.

Physiology, biochemistry. Aluminium accumulation demonstrated (very commonly).

Geography, cytology, number of species. World distribution: pantropical and subtropical. X = 7–18 (or more). 4400 species.