Beautiful Oak Flowers

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Flowers! That is one of many things horticulturalists think of when we think spring. We think of the beautiful flowers of things like Malus, Forsythia, Viburnum, and Quercus. I know, you might be asking, “Quercus, really?” Indeed oaks. Oaks have spectacular flowers! These often-overlooked flowers and quite intricate and showy in their own right. The yellow male catkins appear in the spring and set forests aglow.


According to Michael Dirr, author of The Manual of Woody Landscape Plants, catkins are “A spike-like inflorescence comprised of scaly bracts subtending unisexual flowers, often somewhat flexuous and pendulous but not necessarily so.”

Male Catkins
Male catkins of Quercus montana

The most visible catkins are the male catkins on any catkin-producing plant, with the female flowers being in the form of a catkin or a spike (such as on oaks). Male catkins are composed of many male flowers on a central stem. The catkins mature over one to two weeks and once mature, shed their pollen for three to four days.

Male Catkins
Mature Quercus muehlenbergii. Note the pollen grains.
Immature  Male Catkins
Immature male flowers





Trees bearing catkins are wind pollinated, relying on wind to carry pollen to the female flowers. As you can imagine, with such a pollination strategy these trees must produce large amounts of pollen. Even as a seasonal allergy sufferer I can’t resist flicking a newly opened male catkin and watching the yellow puff of pollen be carried off into the wind.

Female flowers
Female flowers of Quercus bicolor.




Quercus macrocarpa
Quercus muelhenbergii female flowers.

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Further Reading

How do Acorns Develop? University of Tennessee Extension

Arnold Arboretum

Michael Dirr, The Manual of Woody Landscape Plants