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INTRODUÇÃOO gênero Mimosa L. compreende cerca de 530 binômios válidos, em sua grande maioria da região Neotropical, havendo 31 espécies na ilha de Madagascar e um número menor no leste da África e sudeste da Ásia (Coutinho, 2009 The wood anatomical structure of Mimosa balduinii is described, based on material collected in Rio Grande do Sul State, Brazil. In addition to short vascular elements, simple perforation plates, alternating and vestured vessel pits, paratracheal parenchyma and libriform fibers, that are features of common occurrence in Fabaceae woods, the studied species shows large rays, mostly 3-4-seriated, and up to 70 cells height, a rare aspect among Mimosa woods, although observed in M. micropteris, that belongs to the same series Myriophyllae Benth. Unlike this species, however, Mimosa balduinii presents homogeneous rays.