O Gênero Croton L. seção cyclostigma Griseb. e seção Luntia (Raf.) G. L. Webster (Euphorbiaceae) ocorrentes na Amazônia brasileira

Abstract

Euphorbiaceae is one of the larger, complex and diversified families of Angiosperma, including 317 genera and 8,000 species approximately. It is specially distributed in the Tropics, in the most variable types of vegetation and habitat. In Brazil, it is represented by 72 genera and 1,100 species with different habits and habitats, occurring in ali vegetation types. This study, which encloses 7 species of Croton L., has as main objective to modernize the Euphorbiaceae's taxonomy, specially considering genera and species with geographical distribution concentrated in the (Brazilian or International) Amazônia, as well as to carry out morpho-anatomic studies with the selected species as a further help for their correct identification. Through morpho-anatomic characters, we intend to clarify the boundary of close related species, such as C. urucurana and C. draconoides, which affinities still rather confuse. The results aim at to contribute for a better understanding of the diverse section and subsections proposed to organize the genus Croton. It was observed that the trichome types and the flower position at the inflorescences are very important for the identification of the studied species. The leaf architecture study allowed the separation of the species by the presence or absence of sheathing, trichome type, druses, pair number of secondary veins, presence of secondary veins, and type of lignifications of vascular bundle. In conclusion, the morphologic characters allied to the anatomic characters allow a more accurate identification of the species treated in this work.