Abstract Mesosetum is a Neotropical genus with 25 species, and 21 of them occur in Brazil. Mesosetum forms a clade closely related with Keratochlaena rigidifolia and Tatianyx arnacites. The objective of this work was to establish the taxonomic value of the upper anthecium micromorphology for the group. A total of 96 specimens, representing all Mesosetum species (except M. wrightii), K. rigidifolia and T. arnacites were examined under a scanning electron microscope (SEM). PCA and UPGMA analysis were applied using the micromorphologicalcharacters. Fifithteen useful taxonomic characters were identified. We highlight the following characters to distinguish the Mesosetum species: the presence, type and distribution of papillae on the abaxial surface of the upper lemma; the presence of unicellular macrohairs and bicellular microhairs; presence or absence of silica cells and the structure of the germination lid. The present work shows that the micromorphological characters identified are important taxonomically at the specific level, allowing the species identification in many cases.

Abstract Cyperus is a Pantropical genus and the second richest in species in Cyperaceae. It encompasses about 550 species worldwide, with about 100 of these occurring in Brazil. Studies on the taxonomy of this genus are scarce and punctual in Brazil. In this study, the occurrence of species was surveyed through 27 collecting expeditions across different regions in the state of Rio Grande do Norte and analyzis of specimens of several herbaria. Twenty four species of Cyperus were identified, including six new occurrences and one new species, here described, but that will be properly published in other work. This study includes a dichotomous key for the identification of the species, as well as illustrations, descriptions, taxonomic comments and geographical distribution.

O rio Apodi-Mossoró, inserido no Bioma Caatinga, tem seu curso caracterizado por diversidade de ambientes úmidos e representantes da família Cyperaceae. Estudos sobre a flora de Cyperaceae são escassos na região Nordeste do Brasil e inexistentes para o Estado do Rio Grande do Norte. Foram realizadas 21 coletas mensais no período de julho de 2007 a maio de 2008, em quatro pontos principais, nos municípios de Felipe Guerra, Governador Dix-Sept Rosado, Luís Gomes e Mossoró. Registrou-se a ocorrência de 25 espécies distribuídas em sete gêneros de Cyperaceae no rio Apodi-Mossoró, 21 das quais são novas ocorrências para o Estado do Rio Grande do Norte, mais que duplicando o número de espécies de Cyperaceae conhecidas para o Estado. São fornecidas descrições botânicas, comentários taxonômicos, chaves de identificação e ilustrações.

The Apodi-Mossoró River, located in the Caatinga biome, has its course characterized by diverse landscape sand humid environments, as well as by many members of the family Cyperaceae. Studies on the flora of Cyperaceae are scarce in northeastern Brazil and nonexistent for Rio Grande do Norte State. Twenty-one botanical expeditions were undertaken in this area during the period from July 2007 to May 2008 on four main points in the municipalities of Felipe Guerra, Governador Dix-Sept Rosado, Luís Gomes, and Mossoró. Seven genera and twenty-five species of Cyperaceae were found in the Apodi-Mossoró River, twenty-one of which are new records for Rio Grande do Norte State.This figure more than doubled the number of species of the family known to occur in this Brazilian State. Botanical descriptions, taxonomic comments, identification keys, and illustrations are provided.