Chaetogastra is a genus of approximately 115 species of flowering plants in the family Melastomataceae, within the order Myrtales. The genus encompasses herbs, subshrubs, shrubs, and small trees distributed across tropical and subtropical regions of the Americas.
Plants in this genus share a distinctive floral architecture: flowers are hypogynous, with a bell-shaped hypanthium that is typically covered in dense hairs (pubescent) on the outside. The petals number four or five and are most commonly dark lilac to purple, though white, yellow, or deep red forms occur. Stamens number eight or ten and may be uniform or arranged in two series of differing sizes; the connectives at the anther bases are prolonged, bearing two ventral lobes. Seeds are numerous, cochleate (spiral) in shape, and are enclosed in a dry, semi-woody capsule. Leaves are opposite and petiolate, and the inflorescence is a terminal panicle or a modification thereof.
The genus was established by Augustin de Candolle in 1828 but was largely absorbed into a broadly circumscribed Tibouchina by Alfred Cogniaux in his 1885 treatment for Flora brasiliensis. That broad concept accumulated around 470 taxa and persisted for more than a century. Molecular phylogenetic analyses in 2013 and 2019 demonstrated that the broadly circumscribed Tibouchina was paraphyletic, comprising four distinct monophyletic clades with morphological, molecular, and geographic support. The 2019 revision re-established Chaetogastra as a separate genus alongside a more narrowly defined Tibouchina, the re-established Pleroma, and the newly described Andesanthus.
Distribution
Chaetogastra species are native from Mexico through Central America and the Caribbean, continuing south along the Andes through Venezuela, Colombia, Ecuador, Peru, Bolivia, and Argentina, with additional occurrences in eastern Brazil. The Andean zone is the centre of diversity for the genus. Most species inhabit cloud forests at elevations above 1,000 m, while some herbaceous species occur in open habitats at lower elevations above 100 m.
Taxonomy Notes
Chaetogastra was first described by Augustin de Candolle in 1828, then folded into a broadly circumscribed Tibouchina by Alfred Cogniaux in 1885 along with nearly 470 other taxa. Molecular phylogenetic studies in 2013 and 2019 showed that broad Tibouchina was paraphyletic, leading to its split into four genera: a narrower Tibouchina, the re-established Pleroma and Chaetogastra, and the new genus Andesanthus. The placement of Chaetogastra relative to Brachyotum varied between analytical methods in the 2019 study.
