Pollen morphology of the Brazilian species of Bernardia Houst. ex Mill. and Tragia L. (Euphorbiaceae, Acalyphoideae)
ABSTRACT Bernardia and Tragia are the largest genera of the tribes Bernardieae and Plukenetieae (Euphorbiaceae,), with 68 and 125 species, respectively. Very few palynological studies have focused specifically on these genera in spite of the great pollen diversity observed in the family. The present study analyzed the pollen morphology of the Brazilian species of Bernardia and Tragia to identify diagnostic characteristics that could aid in their taxonomic circumscription. The pollen grains of 11 species of Bernardia and five of Tragia were obtained from specimens deposited in the HRB, HUEFS, PEUFR, RB and UFP herbaria, and were analyzed using light and scanning electron microscopy. The analyzed species had small- to medium-sized pollen grains in monads, with shapes from prolate to subprolate. The most significant differences were observed in aperture type and exine ornamentation. The pollen grains of Bernardia are tricolporate, with aperture margins varying from narrow to wide or with just slightly evident margins, and the exine varying between microreticulate and microreticulate-perforate. The pollens of Tragia are tricolpate with the exine varying between intectate pilate and verrucate. Some species of both genera could be diagnosed based on unique pollen characters, and four distinct morphological groups of Bernardia and two of Tragia were observed.