Pollen morphology and its taxonomic potential in Stachytarpheta sect. Stachytarpheta (Verbenaceae) occurring in Brazil

Abstract

Verbenaceae is an important element of Neotropical flora, and Stachytarpheta is the second largest genus in the family. Whereas pollen morphology has helped in the differentiation of several taxonomic groups, palynological data on Stachytarpheta are still scarce, especially for Brazil, where its greatest species richness is concentrated. The present work aimed to analyze the pollen morphology of selected species of Stachytarpheta sect. Stachytarpheta, to aid in the taxonomy of the group. Pollen grains from 11 species were analyzed before and after chemical treatment, measured and treated statistically; multivariate analyses were also performed. The pollen grains of S. sect. Stachytarpheta are large or very large monads, that are radially symmetric and isopolar, with amb varying among triangular, subtriangular, subcircular, and quadrangular, and shape among subspheroidal, oblate-spheroidal, prolate-spheroidal, and subprolate. The three or four apertures are of the colpus type and narrow. The ornamentation is verrucate, with perforations at the base of the verrucae and isolated granules. The pollen grains also possess a margin and an anapertural membrane, which are the main characteristics useful for differentiating the species of the section. The size, amb, shape, apertural type, and ornamentation are also important for morphological differentiation, but multivariate analyses did not support the groups formed based on pollen characterization. An identification key is provided to distinguish the 11 studied species based on pollen morphology.