Palynotaxonomy of Neotropical species of Dioscorea L. (Dioscoreaceae)

Nineteen Neotropical species of the genus Dioscorea L. were subjected to palynological analysis with the objectives of increasing palynological knowledge and identifying characteristics with taxonomic and phylogenetic value. More specifically, the aim was to identify characters that distinguish species and help to resolve relationships among New World clades (i.e. clades NW I, NW II and NW III). Botanical material was obtained from exsiccates deposited in various herbaria. Pollen grains were treated by lactic acetolysis, measured, described, photomicrographed and submitted to statistical analysis. Non-acetolyzed pollen grains were deposited on carbon tape for scanning electron microscopy analysis. The results separate species of Dioscorea into six pollen types based on sexine ornamentation: reticulate, perforate, microreticulate, vermiculate, rugulate and spiculate. The pollen grains of species of Dioscorea are characterized by having monosulcate and disulcate apertures, sometimes in the same specimen (e.g. D. anomala, D. campestris and D. glandulosa). Traditionally accepted taxonomic sections of Dioscorea were not corroborated. Reassessment of established subgenera awaits a better understanding and recognition of phylogenetic lineages.