According to Lorenzi (1996), the Arecaceae family is one of the most common among the monocotyledons, with about 300 genera and approximately 3500 species. Among these, Oenocarpus bacaba Mart., commonly known as bacaba, was selected for study, aiming to broaden the knowledge regarding the structural organization of the tissues, subsidizing taxonomic studies. The samples were collected from the Zoobotanical Park of the Emílio Goeldi Museum of Pará (MPEG), Belém, PA, Brazil. The material was fixed in FAA70%, using the usual techniques in plant anatomy. In frontal view, the epidermal cells of the costal and intercostal regions of the adaxial face are isodiametric and hexagonal; on the abaxial face, the intercostal epidermal cells are heterodimensional and without defined organization while the costal epidermal cells are generally rectangular and follow the direction of the veins. As for the epidermal appendages, tetracyclic stomata and pluricellular shield trichomes were observed. The mesophyll is dorsiventral with two to three layers of paliçadic parenchyma and lacunose parenchyma formed by polygonal cells, occurring nests of fibers, sclereids and vascular bundles, involved by external parenchymatic sheath and internal fibrous sheath continuous or not. Although most of the anatomical characteristics observed have been cited by Tomlinson (1961) as being common to the Arecaceae, this author's considerations to the genus Oenocarpus are rare, allowing the conclusion that in the species studied characteristics occur that individualize the taxon.
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