Pollen morphology of heterostylous species in Piriqueta (Passifloraceae s.l.)

Most of the genus Piriqueta occur in Brazil (39 out of 45 species), with a center of distribution in Bahia State. In this study, we conducted a palynological investigation of 20 heterostylous (distylous) species of the genus Piriqueta, including specimens from both floral morphs of 13 species. Pollen grains were examined, measured, and illustrated by using light and scanning electron microscopy. Pollen morphology was described in terms of shape, size, aperture, and exine ornamentation. Morphometric data were subjected to principal component analysis and hierarchical clustering. Examination revealed pollen grains arranged in monads, isopolar, 3-colporate, with great variability in shape (prolate, subprolate, prolate spheroidal, oblate spheroidal, or suboblate), endoaperture lalongate, polar area small or very small, exine ornamentation most commonly microreticulate or reticulate, sometimes perforate, sexine usually thicker than nexine. Piriqueta sulfurea was an exception, presenting verrucate exine ornamentation. Brevistylous pollen grains were larger in diameter in 75% of the specimens analyzed, whereas mostly longistylous pollen had larger colpi and smaller polar area, but there is no consistent pattern of variation from a specific morph. Even so, those variation underscore the importance of indicating the floral morphs used or, whenever possible, encompassing all existing morphs in pollen descriptions of heterostylous species.