Pollen morphology of Passiflora section Granadillastrum (Passifloraceae) with a detailed description of the aperture

Abstract

Passiflora subgenus Passiflora possesses about 236 species divided into six supersections, among which Stipulata with Granadillastrum is one of its sections. The objective of the present study was to analyse the pollen morphology of 19 species subordinate to the section Granadillastrum and to identify attributes important for the taxonomy of the group. Pollen grains were acetolysed, measured, described and illustrated under light and scanning electron microscopy. Two pollen types differing in polarity were found in the section: Pollen Type I with apolar pollen grains and Pollen Type II with isopolar pollen grains. Type I included large, colpate pollen grains (varying from six to nine colpi), while Type II included large, 6-syncolpate or 3-colpate pollens. All of the studied species had a reticulate exine, sinuous muri, continuous with or without perforations, and ornamented lumina. Hierarchical cluster analysis and principal component analysis (PCA) were used to interpret the formation of the principal pollen groups based on morphology. Two of the analysed species of section (Passiflora imbeana and P. setulosa) are at risk of extinction. The present study is extremely important for characterising pollen morphology such that taxa can be delimited and knowledge acquired for conservation purposes. Five of the studied species had their pollen characterised for the first time, which will be useful to future taxonomic and phylogenetic analyses. This species have pollen characters, such as the number and type of apertures that are important for delimiting some species, while ornamentation in general is similar among taxa and characterises the section.