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Are There Male & Female Oak Trees?

An oak tree at sunrise with the sun shining through its branches.
James Warwick/The Image Bank/GettyImages

Oak trees (‌Quercus‌ spp.) are long-lived, acorn-producing trees. There are about 500 species of oak trees, which grow all over the world. About 90 of those species are found in North America.

While in other types of trees there are separate male and female specimens, this distinction does not exist among oak trees, which have both male and female flowers.

Are Trees Male or Female?

All plants that reproduce via seeds, which includes trees, are either dioecious or monoecious. In dioecious tree species, there are separate male and female trees that contain different reproductive organs. In monoecious species, male and female components are located on the same tree.

Oak trees, which are flowering trees, are considered monoecious because each tree contains both male and female flowers. In some plants, a single flower contains both male and female organs. These are known as perfect flowers.

However, oak tree flowers are either fully male or female, explains the University of Tennessee Extension. Male oak tree flowers produce the pollen that must fertilize the female egg, known as an ovule, in order for the plant to produce seeds and in some cases, fruit.

Oak tree flowers are either fully male or female, and each tree contains both male and female flowers. However, the female flowers must be cross-pollinated by a ‌different‌ oak tree specimen in the vicinity.

Catkins: Oak Trees' Male Flowers

In the springtime, pendulous growths that feature small flowers along a stem can be seen on oak trees. These are the tree's male flowers, and they are referred to as catkins. They usually emerge in early spring before leaf out, though the timing depends on the species and temperatures.

Catkins are usually very showy. In contrast, the female flowers of oak trees are small to the point that they are easily missed. They are also easily mistaken for leaf buds because they emerge from the base of leaves on new twigs.

Oak tree catkins are also easier to spot because they are found on the lowest portion of the tree. Female oak tree flowers, on the other hand, are located high in the canopy, explains the Cornell Cooperative Extension, which is why passersby are unlikely to see them. Female flowers open about two weeks after the male flowers.

How Are Oak Trees Pollinated?

Oak trees are pollinated by the wind—that is, the wind carries the pollen produced by male flowers to the part of female flowers known as the stigma. The pollen swirling in the air can trigger springtime allergies in people who are sensitive.

Even though oak trees all have both male and female flowers, the latter must be pollinated with the pollen of a ‌different‌ oak tree specimen in the vicinity. This is known as cross-pollination. The placement of the female flowers above the male flowers in oak trees prevents pollen from an oak tree from drifting down to the female flowers of the same tree.

Pollination is required for oak trees to produce fruit—in their case, acorns. A number of factors can interfere with this process, including cold temperatures that damage female flowers and excessive rain and humidity that wash away pollen produced by male flowers or make it too heavy and sticky for the wind to transport.

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