Tibouchina triprovincialis, a new species of Melastomataceae from the Southwestern Amazonian grasslands

Tibouchina triprovincialis is a new species collected in the Brazilian states of Amazonas, Mato Grosso, and Rondônia. All gatherings from Amazonas and Rondônia come from the “Parque Nacional dos Campos Amazônicos”, while the single gathering outside it comes from northwestern Mato Grosso. Dense and extensive populations of this small shrub occur in “hyperseasonal savannas”, i.e. savannic enclaves in the middle of the Amazonian rainforest, with a thick herbaceous layer and very few shrubs or trees, growing on poorly drained soils. Tibouchina triprovincialis differs from both T. aspera and T. spruceana by the smaller leaves, with shorter petioles, 0.6–1.5 mm long (vs. 3–10 mm in T. spruceana, 2–10 mm in T. aspera) and blades 5–11 mm long (vs. 20–50 mm in T. spruceana, 20–80 in T. aspera), the abaxial surface densely covered with broad scales that conceal the surfaces of veins and the actual surfaces between the veins (vs. moderately covered with slender scales or trichomes that do not conceal the surfaces beneath, on both the veins and the actual surfaces between the veins). As for extinction risk, we suggest that T. triprovincialis should be regarded as “Least Concern” (LC).