The ultimate function of pollen is to deliver male gametes (sperm) from the stamen of a plant to an ovule for fertilization of an egg, which then develops into a seed.
Pollen is an evolutionary development found in highly derived plants?angiosperms and gymnosperms?that protects the gametes and allows for fertilization without water and gives pollen-producing plants the ability to disperse their gametes farther and in more diverse environments than more primitive seedless plants.
Seedless vascular plants and bryophytes lack pollen and instead release flagellated sperm that require at least a film of water through which to swim to the egg.
Wind or a pollinating animal can spread pollen, and pollen morphology shows which of these vectors a plant species prefers. Smaller, smoother pollen usually is wind dispersed, while larger, spinier varieties evolved to attach to pollinators.
Each pollen grain has a sporopollenin-coated shell that contains non-reproductive vegetative cells, male gametes and a cell that forms a pollen tube upon contact with the ovule.
Allergic reactions to airborne pollen grains are common among humans. They are often referred to as hay fever.