Pollen is a fine to coarse powder consisting of microgametophytes (pollen grains)which produce the male gametes (sperm cells) of seed plants. There are remarkable processes involved in pollen adhesion & stigma pollen interaction. There are also mysteries with regard to self pollination.
The 500x image above shows no Passiflora pollen but gives an idea of pollen diversity across different Genera. Even within the Passiflora Genus their pollen grains show remarkable diversity. Despite this there are surprisingly few studies of them or published images. Thanks to the kindness of Frans Holthuysen, Dr Clive Steele and others, this site has a unique archive of Passiflora species and hybrid SEM images here.
A short study by Fabiola Areces under the supervision of Dr. Joan W. Nowicke at The Smithsonian Institution found that,
''Within the ten taxa of Passiflora, two pollen types, both of which are thick walled, can be recognized: I. Pollen is 6-zonocolporate with fusiform opercula, and lacks free columellae in the lumina (not examined in TEM ); II. Pollen could be interpreted as 3-colpate with very large ovate opercula, has free columellae in lumina, a massive endexine and lacks foot layer. Pollen of Adenia hastata is thin walled, 5-6 zonocolpate, and lacks opercula, Pollen of Tetrapathaea tetranda is thin walled, 3-colpate with strap-shaped opercula, lacks free columellae, has prominent endexine only under aperture and has a foot layer. The four pollen types described above can be easily distinguished from each other even in LM. This study is one of the first attempts to document the structure of the exine of Passiflora using TEM.''