Oaks are members of the genus Quercus. These broadleaf hardwood trees are highly valued for the quality of their lumber and their decorative value. Like all other flowering plants, they are sexually reproducing species.
Oak trees are monoecious, meaning that they have male and female flowers on the same plant. Unlike many other flowering plants, however, they have separate male and female flowers. The male flowers produce pollen, while the female flowers produce eggs that will be fertilized once the flowers are pollinated.
Each oak tree is essentially both male and female, since it features both male and female flowers. The male flowers are small structures on stalk-like appendages called catkins; the catkins droop down from some of the branches. Female flowers are so small they are best identified with a magnifying glass. They are found on twigs near the base of emerging leaves, where they appear a week or so before the male flowers.
Oak trees are primarily wind-pollinated. The male flowers generate ample pollen to ensure that at least some of it will reach its intended targets. Although oak trees have both male and female flowers, female flowers typically are pollinated by the pollen of another tree.