Pollen morphology of Brazilian Aristolochia subgenera Aristolochia (Aristolochiaceae) and its taxonomical significance

Aristolochia (Aristolochiaceae) comprises about 550 species and especially in the Neotropical region where this genus is highly diverse few studies of palynological characterization have been conducted. To better understand the pollen morphology of the genus, pollen grains of 25 species were examined, of which one belongs to Aristolochia subgenus Siphisia and 24 to Aristolochia subgenus Aristolochia (three of Aristolochia series Thyrsicae; eight of Aristolochia series Hexandrae subser. Anthocaulicae , and 13 of Aristolochia series Hexandrae subseries Hexandrae ). Pollen grains are radially symmetrical, apolar, inaperturate and spheroidal. Under SEM, ornamentation patterns of the exine are fossulate (19 species), fossulate-areolate (four species), microfossulate (one species) and verrucate (one species). Most species have pollen with perforated surface except A. gibertii , A. holostylis , A. pohliana , and A. ridicula . Results corroborate that the micromorphological features, such as pollen shape and aperture absence are similar in all species of Aristolochia , but for some species exine ornamentation might be useful for taxonomic distinction at the species level.