Chinese hibiscus and its pollen. Computer illustration of pollen grains on the anther of a Chinese hibiscus (Hibiscus rosa-sinensis) flower. Pollen grains are the male gametes (sex cells) of a plant. The grain has a highly sculptured outer wall (exine), which may assist in its dispersal by improving its adherence to pollinating insects. The characteristic surface of a pollen grain is used by botanists to recognise and classify plants. Pollen grains are microscopic, usually about 15 to 100 microns across, and just a pinch of pollen powder contains thousands and thousands of grains. Hibiscus belongs to hypoallergenic plants usually not causing seasonal allergy.