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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.

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