Pollen morphology of Alcantarea giant bromeliads (Bromeliaceae, Tillandsioideae)

Abstract

Here we describe the pollen morphology of 19 species of Alcantarea, none of them fully described before, to contribute to the infra-generic delimitation of the genus. Pollen grains are heteropolar, amb ellipsoidal (although spheroidal pollen occurs in Alcantarea aurantiaca, A. burle-marxii, A. glaziouana, A. nahoumii, A. roberto-kauskyi and A. trepida), monosulcate, sulcus with margin, reticulate ornamentation of the exine on the central area of pollen grain (except in A. imperialis, which display foveolate ornamentation) and apex of equatorial axe with different ornamentation from the central area of pollen grain (microreticulate calota or psilate-perforate calota). The genus is considered stenopalynous due to the similarity in the pollen morphology. The new pollen characters obtained here are useful in understanding the infra-generic palynotaxonomy of the genus confirming the relationship between species that have been grouped together based on vegetative evidence and/or relationships suggested by analyses based on DNA sequences or microsatellite evidence, e.g. between A. aurantiaca, A. burle-marxii and A. nahoumii; between A. burle-marxii, A. glaziouana and A. trepida; between A. hatschbachii and A. duarteana, between A. roberto-kautsky and A. trepida. Our results improve the morphological characterisation of the genus and may contribute to phylogenetic analyses as well as the biosystematics approach to solve species complexes.