ABSTRACT The present study aimed to morphologically characterize the pollen grains of species of Brasiliocroton mamoninha and B. muricatus in order to expand palynological knowledge of the group and provide additional micromorphological information useful for studies of the relationships within Crotoneae. Polleniferous material was acetolysed and described using light, scanning electron and transmission microscopy. The pollen grains of the two species of Brasiliocroton were apolar, spherical, inaperaturate and medium-sized with a Croton ornamentation pattern. The Croton pattern of B. mamoninha is formed by subtriangular pila, >5-plicate with pointed apices, while for B. muricatus it is formed by subcircular to circular pila, <5-plicate with rounded apices. Ultrastructural analysis revealed a stratified sexine in both species, whereas variation in the pattern of deposition of the foot layer allowed the species to be palynologically distinguished from each other. The composition of the Croton pattern of ornamentation, the morphology of the ultrastructure of the wall and the range of variation in the diameter of the pollen grains differed between the studied species, and thus are diagnostic characters. Pollen morphology allowed the two species of Brasiliocroton to be palynologically separated, and provided data that will be useful for taxonomically circumscribing these taxa.

Este estudo foi baseado na análise de materiais de herbário, referências bibliográficas e coletas, revelando a ocorrência de 35 espécies do gênero Croton para o estado de Pernambuco. A maior parte destas espécies tem distribuição exclusiva na zona fitogeográfica das Caatingas; Croton fuscescens Spreng., C. grewioides Baill. e C. blanchetianus Baill. estendem-se da zona da Mata até a zona das Caatingas; C. polyandrus Spreng. e C. sellowii Baill. ocorrem principalmente na faixa litorânea, em vegetação de restinga; C. argenteus L., C. jacobinensis Baill. e C. triqueter Lam. foram observados apenas na zona da Mata, e C. glandulosus L., C. heliotropiifolius Kunth, C. hirtus L' Her. e C. lundianus (Didr.) Müll. Arg. apresentam ampla distribuição no Estado. São apresentadas chave de identificação, comentários sobre distribuição geográfica e habitats, juntamente com ilustrações de características diagnósticas das espécies.

This study was based on the analysis of herbarium material, specialized bibliography and field collections, recording the occurrence of 35 species of the genus Croton for the state of Pernambuco. Most of these species are distributed exclusively in the Caatinga phytogeographic region; Croton fuscescens Spreng., C. grewioides Baill. and C. blanchetianus Baill. are found from the forest zone to the caatinga zone; C. polyandrus Spreng. and C. sellowii Baill. occur mainly along the coast, in restinga vegetation; C. argenteus L., C. jacobinensis Baill. and C. triqueter Lam. were observed only in the forest zone, and C. glandulosus L., C. heliotropiifolius Kunth, C. hirtus L' Her. and C. lundianus (Didr.) Müll. Arg. are widely distributed. Identification keys, comments on geographic distribution and habitats and illustrations of diagnostic characteristics of the species are provided.

RESUMO O gênero Croton é o segundo maior e mais diverso em Euphorbiaceae, possuindo cerca de 1.200 espécies, difundidas predominantemente no continente americano. Este estudo foi baseado na análise morfológica de materiais herborizados e na observação das plantas em campo. Foram registradas 15 espécies, apenas C. heliotropiifolius com ampla distribuição na área de estudo, ocorrendo em vegetação de caatinga. Croton adamantinus, C. corchoropsis, C. nummularius, C. rudolphianus e C. virgultosus são encontradas apenas no complexo arenítico das serras da chapada de São José, em Buíque, crescendo em vegetação rupestre. São fornecidos chave para identificação, comentários sobre as afinidades entre os táxons e distribuição geográfica, bem como ilustrações de todas as espécies estudadas.

ABSTRACT Croton is the second largest genus in Euphorbiaceae, with about 1,200 species, distributed predominantly in the Americas. This study was based on herbarium material and field observations. A total of 15 species was recognized, only C. heliotropiifolius with wide distribution in the study area, occurring in caatinga vegetation. Croton adamantinus, C. corchoropsis, C. nummularius, C. rudolphianus, and C. virgultosus are found only in the sandstone complex of São José plateau, Buíque, growing up in rocky vegetation. Identification keys, descriptions, comments about morphological relationships and geographic distribution, and illustrations of species are provided.