Pollen was a powder consisting of microgametophytes (pollen grains), which producesd the male gametes (sperm cells) of seed plants. The process of disseminating it was known as pollination. (VOY: "Elogium", "Tuvix")
Toxic pollen produced by psychotropic flowers on the planet Archer IV, the first planet visited by Enterprise NX-01, contained tropolisine and caused paranoia and hallucinations in humanoids. (ENT: "Strange New World")
Malcolm Reed was allergic to oak pollen, as well as bromelain, dust mites and tropical grasses. (ENT: "Silent Enemy")
Bees, Earth insects that made the key ingredient in beeswax candles, gathered pollen from flowers. (TNG: "A Fistful of Datas")