Pollen

Pollen is the fine powder of microscopic grains that carry the male gametes of seed plants. Each grain is the male gametophyte, and it must reach a female structure for fertilization to occur.

A pollen grain is a few tens of micrometers across and has a tough outer wall, the exine, made of sporopollenin, one of the most resistant biological polymers. The wall's patterns and pores are characteristic of each plant group. Inside are a few cells that produce the sperm cells, which are delivered by a pollen tube that grows into the flower.

Conifers, grasses and many trees release large amounts of pollen that is carried by the wind, while most flowering plants rely on insects, birds or bats that are rewarded with nectar. Pollination by animals is a major force behind biodiversity, and the partnership has driven the evolution of flower shapes and colors.

Pollen of ragweed, grasses and birch triggers hay fever in many people. A 2021 analysis of North American data found that pollen seasons lengthened by about 20 days and concentrations rose by about 21 percent from 1990 to 2018, linked to warming, as discussed in the health effects of climate change. Because sporopollenin survives for millions of years, fossil pollen in lake sediments records vegetation and climate for paleoclimatology.

• Plants — the organisms that make pollen
• Gametes — the sex cells that pollen delivers
• Paleoclimatology — a field that uses fossil pollen