Pollen variability in species of Dioscorea L. (Dioscoreaceae)

Dioscoreaceae is characterised by wide morphological variability, including hermaphrodite genera such as Tacca J.R.Forst. et G.Forst, Trichopus Gaertn., and Stenomeris Planch. and some dioecious species in the genus Dioscorea L. This study aimed to describe the pollen characters of 81 species of Dioscorea occurring in Brazil, contributing to a broader knowledge of Dioscoreaceae by investigating the possibility of using pollen attributes in taxonomic classification. Pollen grains were treated by lactic acetolysis, measured, described, and photomicrographed. The results were subjected to statistical analysis. Unacetolysed pollen grains were mounted on stubs with carbon tape for scanning electron microscopy. Our results showed that the studied species have heteropolar pollen grains, ranging from small to medium, with mainly elliptical, circular, and triangular ambs. Pollen grains with 1, 2, or 1-2 apertures were recorded in most species, as well as nine types of sexine ornamentation (perforate in 23 species, striate in 23 species, microreticulate in 15 species, reticulate in eight species, rugulate in seven species, bireticulate in two species, rugulate-verrucate in one species, cristate in one species, and gemmate in one species). The sexine had striae in different shapes and directions. Micromorphological results of pollen characters were of great importance for species delimitation. The findings reported herein demonstrate that palynological analysis can provide valuable information to improve taxonomic classification and contribute to a more robust phylogenetic representation of the genus.