The following description is used here with permission from L. Watson and M. J. Dallwitz, The Families of Flowering Plants.  In that work, and thus in the following description the Memecylaceae are excluded.  I prefer the broader circumscription of the Melastomataceae that includes the Olisbeoideae (=Memecylaceae) and Melastomatoideae.  Each subfamily is monophyletic and the two clades are sister, thus it is simply a matter of taste.

Melastomataceae Juss.

Habit and leaf form. Herbs, or shrubs, or trees, or lianas. 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. Lamina 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 exstipulate. Lamina margins entire, or serrate. Leaves without a persistent basal meristem. Domatia recorded (about 10 genera); represented by pits, or pockets.

General anatomy. Plants with ‘crystal sand’, or without ‘crystal sand’.

Leaf anatomy. Mucilaginous epidermis present, or absent. Stomata mainly anomocytic.

Lamina without secretory cavities. The mesophyll with sclerencymatous idioblasts (commonly), or without sclerenchymatous idioblasts; containing calcium oxalate crystals (variously raphides, styloids, druses and crystal sand). Minor leaf veins without phloem transfer cells (Heterocentron, Medinilla, Tibouchina).

Stem anatomy. Young stems often tetragonal. Cork cambium present; initially deep-seated, or superficial. The cortex containing cristarque cells (Osbeckieae), or without cristarque cells. Nodes unilacunar. Primary vascular tissue bicollateral, or centrifugal. Cortical bundles present (often), or absent. Medullary bundles present (often), or absent (these and cortical bundles present or absent in all combinations). Internal phloem present. Secondary thickening absent (?), or developing from a conventional cambial ring, or anomalous; from a single cambial ring. ‘Included’ phloem present (often), or absent. Xylem with fibre tracheids (rarely), or without fibre tracheids; with vessels. Vessel end-walls simple. Vessels with vestured pits. Wood parenchyma paratracheal (only, in most genera), or apotracheal and paratracheal.

Reproductive type, pollination. 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, floral, fruit and seed morphology. 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); calyptrate, or not calyptrate; regular, or somewhat irregular. The floral irregularity 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 lobulate, or blunt-lobed, or toothed; regular; calyptrate, or not calyptrate; imbricate, or valvate, or contorted, or open in bud. 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); in the same series as the fertile stamens. 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. Endothecium not developing fibrous thickenings (thin and non-fibrous or even ephemeral). Anther epidermis persistent. Microsporogenesis simultaneous. The initial microspore tetrads tetrahedral, or isobilateral, or decussate. Anther wall initially with one middle layer, or initially with more than one middle layer (up to 7). Tapetum glandular. Pollen grains aperturate; (2-)3(-6) aperturate; colporate, or colpate and colporate (typically tricolporate, with three alternating poreless furrows (‘pseudocolpi’); 2-celled (Tobe and Raven 1984).

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 (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); bitegmic; crassinucellate. Outer integument contributing to the micropyle (in addition to the inner one). Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; not proliferating; ephemeral. Synergids hooked. Hypostase present. Endosperm formation nuclear. Embryogeny onagrad, or solanad.

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. Cyanogenic, or not cyanogenic. Cynogenic constituents phenylalanine-derived (?). Alkaloids usually absent. Iridoids not detected. Proanthocyanidins present, or absent; when present, cyanidin and delphinidin. Flavonols present, or absent; kaempferol, or kaempferol and quercetin, or quercetin and myricetin. Ellagic acid present (5 genera, 5 species). Saponins/sapogenins absent. Aluminium accumulation demonstrated (very commonly). Anatomy non-C4 type (Melastoma).

Geography, cytology. Sub-tropical to tropical. Pantropical and subtropical. X = 7-18 (or more).

Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Myrtiflorae; Myrtales. Cronquist’s Subclass Rosidae; Myrtales. APG (1998) Eudicot; core Eudicot; Rosid; Eurosid II; Myrtales. Species about 4400. Genera about 180; Acanthella, Aciotis, Acisanthera, Adelobotrys, Allomaieta, Allomorpheia, Allomorphia, Amphiblemma, Amphorocalyx, Anaectocalyx, Anerincleistus, Antherotoma, Appendicularia, Arthrostemma, Ascistanthera, Astrocalyx, Astronia, Astronidium, Axinaea, Barthea, Beccarianthus, Behuria, Bellucia, Benevidesia, Bertolonia, Bisglaziovia, Blakea, Blastus, Boerlagea, Boyania, Brachyotum, Bredia, Brittenia, Bucquetia, Cailliella, Calvoa, Calycogonium, Cambessedesia, Campimia, Carionia, Castratella, Catanthera, Catocoryne, Centradenia, Centradeniastrum, Centronia, Chaetolepis, Chaetostoma, Chalybea, Charianthus, Cincinnobotrys, Clidemia, Comolia, Comoliopsis, Conostegia, Creochiton, Cyanandrium, Cyphostyla, Cyphotheca, Dalenia, Desmoscelis, Dicellandra, Dichaetanthera, Dinophora, Dionycha, Dionychastrum, Diplarpea, Diplectria, Dissochaeta, Dissotis, Dolichoura, Driessenia, Enaulophyton, Eriocnema, Ernestia, Feliciadamia, Fordiophyton, Fritzschia, Graffenriedia, Gravesia, Guyonia, Henriettea, Henriettella, Heterocentron, Heterotis, Heterotrichum, Huberia, Huilaea, Hypenanthe, Kendrickia, Kerriothyrsus, Killipia, Kirkbridea, Lavoisiera, Leandra, Lithobium, Llewelynia, Loreya, Loricalepis, Macairea, Macrocentrum, Macrolenes, Maguireanthus, Maieta, Mallophyton, Marcetia, Mecranium, Medinilla, Melastoma, Melastomastrum, Meriania, Merianthera, Miconia, Microlepis, Microlicia, Mommsenia, Monochaetum, Monolena, Myriaspora, Myrmidone, Neblinanthera, Necramium, Neodriessenia, Nepsera, Nerophila, Ochthephilus, Ochthocharis, Omphalopus, Opisthocentra, Oritrephes, Osbeckia, Ossaea, Otanthera, Oxyspora, Pachyanthus, Pachycentria, Pachyloma, Phaiantha, Phyllagathis, Pilocosta, Plagiopetalum, Pleiochiton, Plethiandra, Pogonanthera, Poikilogyne, Poilannammia, Poteranthera, Preussiella, Pseudodissochaeta, Pseudosbeckia, Pterogastra, Pterolepis, Rhexia, Rhyncanthera, Rousseauxia, Salpinga, Sandemania, Sarcopyramis, Schwackaea, Scorpiothyrsus, Siphanthera, Sonerila, Sporoxeia, Stenodon, Stussenia, Svitramia, Tateanthus, Tayloriophyton, Tessmannianthus, Tetrazygia, Tibouchina, Tibouchinopsis, Tigridiopalma, Tococa, Topobea, Trembleya, Triolema, Tristemma, Tryssophyton, Tylanthera, Vietsenia.

Description corrected by S.S. Renner (1992).

Cite this publication as: ‘L. Watson and M. J. Dallwitz (1992 onwards). The Families of Flowering Plants: Descriptions, Illustrations, Identification, and Information Retrieval. Version: 14th December 2000.‘. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993, 1995, 2000), and Watson and Dallwitz (1991) should also be cited (see References).