Pollen morphology of the early branching papilionoid legume genera Harleyodendron, Holocalyx and Uribea

Abstract

In this study, pollen grains of Harleyodendron unifoliolatum, Holocalyx balansae, and Uribea tamarindoides, three monospecific genera with Neotropical distribution belonging to the clade Exostyleae, one of the basal lineages of the family Leguminosae, subfamily Papilionoideae, were analyzed. The palynological material was acetolyzed and analyzed under light microscopy (LM) and scanning electron microscopy (SEM). Under LM, small and medium-sized pollen grains were observed, which showed a prolate-spheroidal to prolate shape, 3-colporate, microreticulate and reticulate exine, sexine and nexine of equal thickness in Harleyodendron and Holocalyx, while the sexine was thicker than nexine in Uribea. Analysis under SEM showed finely granulate, psilate, and granulate apertural membrane, while the exine ornamentation varied from perforate-microechinate in Harleyodendron, to perforate in Holocalyx, while in Uribea showed an irregular relief and granular projections on the perforate tectum. The pollen morphology of these species is similar to each other, varying in sexine/nexine ratio, apertural membrane, and exine ornamentation. Harleyodendron has a finely granulate apertural membrane, sexine and nexine of equal thickness, and a perforate-microreticulate exine ornamentation, Holocalyx shows a psilated apertural membrane, sexine and nexine of equal thickness, and exine ornamentation perforate, and Uribea has a granulate apertural membrane, sexine thicker than nexine, and exine ornamentation with granular projections.