Sunflower pollen grains. Coloured scanning electron micrograph (SEM) of pollen grains from the sunflower (Helianthus annuus). The grains have a spiked outer wall (exine), which assists in their dispersal to the female parts of other sunflowers by improving their adherence to pollinating insects. The characteristic surface of pollen grains is used by botanists to recognise and classify plants. Pollen grains are the male sex cells of a flowering plant.