XVI International Botanical Congess
Axonopus is a highly speciose genus of Panicoid tropical grasses. About 110 species were recognized in the systematic treatment proposed by Black in 1963. The species were separated mainly on the basis of vegetative morphological differences and spikelet size variation, among other characters, resulting in a poor definition of many taxa. S.E.M. studies of the spikelets of Axonopus spp. were performed in order to identify new valuable taxonomic characters that could help in species delimitation. Several patterns of lemmatal ornamentation were identified related to the Eriochloa and Brachiaria patterns as described by Hsu (1961), as well as some new patterns not previously described for the Paniceae. The lemmatal ornamentation seems to be useful at identifying groups of closely related species. Some distinct patterns were recognized in A. brasiliensis, A. marginatus, A. fastigiatus among others, pointing to a higher degree of morphological differentiation in these species.