The neotropical genus Retiniphyllum consists of approximately 23 species of shrubs and small trees, most of them occurring in the Guayana region, and with a few species reaching the Amazon basin, Central, and Eastern Brazil. This genus is characterized by having stipules producing copious resinous secretion, inflorescences racemose, spicate or fasciculate, flowers subtended by bracteoles and involucels, corollas white, pink or red, anthers with apical and basal appendages and 5-locular ovary with two collateral ovules per locule. Because of its peculiar morphological features, the taxonomic position of Retiniphyllum has been debated among botanists. Robbrecht placed it in the monotypic tribe Retiniphylleae. Recent phylogenies using molecular data support Robbrecht's placement in this tribe, and indicate that this tribe should be included in the Ixoroideae sensu lato. A phylogenetic analysis using morphological characters was performed analyzing a data matrix with 23 taxa and 42 characters. Sipanea and Sipaneopsis were selected as outgroup. The analysis produced four shortest trees of 169 steps each, where Retiniphyllum appeared to be monophyletic. The morphological cladogram showed that white flowers were derived once in Retiniphyllum. A preliminary phylogenetic analysis using ITS sequences was performed including the nine Retiniphyllum species of which fresh material was available. In the phylogeny obtained, two major clades were formed, which seemed to correspond to Müller's sections Euretiniphyllum (with racemose inflorescences) and Commianthus (with spicate inflorescences). According to the results obtained, there was conflict between the morphological and molecular data. For example, Retiniphyllum speciosum, a species with red flowers, was nested within the white flower species in the molecular cladogram. Because the molecular analyses was performed with only a few species, at this point it is difficult to determine the significance of the incongruence between the molecular and morphological phylogenies.

Key words: Guayana Region, ITS, morphology, Retiniphyllum, Rubiaceae, Systematics