Herbs, perennial, shrubs, or trees [lianas], usually synoecious, [rarely androdioecious], terrestrial, unarmed, not laticiferous, without colored juice, sometimes clonal. Stems erect, ascending-erect, or procumbent, often 4-angled when young; bud scales present. Leaves deciduous or persistent, usually opposite and decussate, 1 of each pair slightly smaller, rarely verticillate or alternate (by abortion of 1 of each pair), simple; stipules absent; petiolate, sessile, or subsessile; blade venation palmate or parallel, no dominant midrib, the several, strong veins diverging at base, converging at apex (acrodromous), usually strongly cross-veined, margins entire, subentire, serrate, serrulate, or crenulate. Inflorescences terminal or axillary, cymes or paniculate cymes (simple or compound dichasia), [umbels, corymbs, cincinni, or, rarely, fascicles, spikes, or flowers solitary]; bracts present, sometimes persistent and color conspicuous; bracteoles present, usually caducous, opposite. Flowers actinomorphic, androecium often slightly zygomorphic; subsessile or pedicellate; perianth and androecium perigynous, biseriate; hypanthium urceolate, campanulate, or globose-urceolate [funnelform, cyathiform]; calyx lobes [0, 3] 4 or 5 [or 6], usually as teeth or lobes on hypanthium rim, valvate (rarely connate), intersepalar segments present; petals (3 or)4 or 5[or 6], equal number to sepals, distinct, imbricate in bud; nectary glands absent [present]; stamens [4, 5] 8 or 10 [12–96], usually 2 times number of petals and in 2 whorls (except 1 whorl in Tetrazygia), or, rarely, equal to petals, isomorphic or dimorphic; filaments distinct, exserted, often geniculate, free of perianth lobes, equal or conspicuously unequal, often twisted, bringing anther to 1 side; anthers basifixed, not versatile, introrse, dehiscent by 1 or 2 apical pores [or by longitudinal slits]; staminodes (0 or)4 or 5; pistil 1, 4- or 5-carpellate; ovary inferior or semi-inferior, 3–5[–14]-locular; placentation axile [parietal or free-central]; style 1; stigma 1, capitate [truncate]; ovules (2–)6–50 per locule, anatropous or (Rhexia) orthotropous, bitegmic, crassinucellate. Fruits berries or capsules, dehiscent or indehiscent. Seeds 20–100, tawny to purple or black, cochleate or cuneate; endosperm absent. x = 7–18+.
North America, Mexico, West Indies, Central America, South America, Asia, Indian Ocean Islands (Madagascar), Pacific Islands, Australia.
Genera 150–170, species ca. 5000 (3 genera, 15 species in the flora).
Species of Melastomataceae occur primarily in tropical and subtropical regions, especially in South America. Miconia Ruiz & Pavon, with ca. 1300 species, is the largest genus in the family; boundaries distinguishing potential generic-level taxa among these species are not clearly resolved. Most Melastomataceae can be recognized as members of the family by their opposite, decussate leaves with acrodromous venation (with three or more primary, arcuate longitudinal veins converging toward the apices and cross-veins at right angles to the primary veins), radially symmetric and diplostemonous flowers, apically dehiscent anthers, stamens often with enlarged and/or appendaged connectives, and relatively numerous small seeds. The species are notable for their diversity of hair types and modifications of the androecium. Molecular-based phylogenies suggest that berries have evolved from capsules at least four times within the family.
Species of some genera of Melastomataceae are grown as ornamentals in warm climates. Tibouchina Aublet (ca. 350 species) is particularly well represented among the cultivars in the United States.
Six genera with ca. 430 species have been treated as a tribe or subfamily of Melastomataceae, or as the separate family Memecylaceae (two of the genera, Mouriri Aublet and Votomita Aublet, are in South America, and four are in southeast Asia; none of them is in the flora area). These plants have primarily pinnate or brochidodromous venation, less commonly acrodromous, which is the ancestral state (R. D. Stone 2006). S. S. Renner (1993) treated them as Memecylaceae; molecular data (G. Clausing and Renner 2001) suggested that the group, along with the closely related Pternandra Jack of southeast Asia, is basal to the Melastomataceae. Angiosperm Phylogeny Group (2009) have placed this group within the Melastomataceae.
|1||Herbs; petals 4; fruits capsules; seeds usually cochleate.||Rhexia|
|1||Shrubs or small trees; petals 4 or 5; fruits berries or capsules; seeds cuneate or cochleate.||> 2|
|2||Leaf surfaces with dense scales abaxially, glabrous adaxially; petals white or pink; fruits berries; seeds cuneate.||Tetrazygia|
|2||Leaf surfaces usually strigose; petals light to dark pink, lavender, or purple; fruits fleshy and irregularly splitting-dehiscent; seeds cochleate.||Melastoma|