Melastomataceae is a tropical family. Its species are scattered across the warm, wet regions of the globe, but the distribution is highly uneven, and that unevenness is one of the most interesting things about the family.
Quick facts. Distribution: pantropical. Centre of diversity: the Neotropics, home to the large majority of species. Old World hotspots: Southeast Asia, Africa and Madagascar. Temperate representatives: very few, such as Rhexia in eastern North America.
The Neotropics: the heartland
Central and South America and the Caribbean hold most of the family's species. Hotspots include the Andes, the Amazon basin, the Guiana Shield, Central America and the Atlantic Forest of Brazil. Brazil's Cerrado and rocky mountain grasslands, called campos rupestres, are also notable, with many shrubby species with narrow local ranges.
Several of the largest genera, such as Miconia, are Neotropical, and so are the tribes that dominate the forest understory.
The Old World
Outside the Americas the family is smaller but still diverse.
- Southeast Asia and the Malay Archipelago: home to genera such as Medinilla, Melastoma, Sonerila and Phyllagathis. See Medinilla and Melastoma.
- Africa: fewer species, including Dissotis and relatives (Africa's showy melastomes).
- Madagascar: a distinct set of species, many endemic.
- India and Sri Lanka: notable for local endemics, especially in the Western Ghats.
- Australia and the Pacific: a limited number of native species, along with several introduced weedy ones.
Temperate outliers
Cold climates are not hospitable to melastomes. A handful of species reach into subtropical or warm-temperate zones, and the genus Rhexia ranges into the eastern United States and Canada. This makes Rhexia a rare case of a melastome you can find on a North American meadow.
Habitats within the range
Within these regions, melastomes occupy an unusually broad spectrum of habitats:
- Rainforest understory, from shaded herbs to tall trees.
- Cloud forests and high mountain shrublands (Andean cloud forest and páramo).
- Epiphytic perches on trees (Blakea).
- Open grasslands and savannahs.
- Rock outcrops and sandy soils.
- Wetlands and stream banks.
Why the Americas?
Exactly why the Neotropics hold so many species is still being investigated. Likely contributing factors include the long history of mountain building in the Andes, which creates isolated habitats and promotes speciation, the size and stability of humid forest regions, and the evolutionary success of particular lineages such as the berry-fruited tribes, whose fruits attract birds that can carry seeds over long distances.
Distribution and invasion
The same family that has narrow endemics also includes widespread weeds. When species from the Neotropics are moved to similar climates elsewhere, some spread aggressively. See why some melastomes are invasive.
Takeaways
- The family is pantropical but strongly concentrated in the Americas.
- The Old World has fewer species but important local diversity.
- Temperate regions have very few melastomes.
- Habitat variety is wide, from forest floor to mountain summits.