The question of whether a tree is male or female is far more complex than the simple binary found in the animal kingdom. Botanical reproduction strategies in trees utilize a spectrum of sexual systems, meaning the terms “male” and “female” only accurately describe a small fraction of species. Understanding these biological mechanisms reveals a diversity of life strategies, often involving a tree possessing both reproductive structures in some form. A tree’s botanical classification dictates whether it produces fruit, pollen, or both, influencing its growth and impact on the surrounding environment.
Understanding Perfect Flowers
The majority of flowering trees are neither exclusively male nor female, employing a strategy that produces perfect flowers. Also known as bisexual or hermaphroditic, a perfect flower contains both the pollen-producing male parts—the stamens—and the ovule-containing female parts—the pistil or carpel—within the same single blossom. The stamen releases the microscopic pollen grains, while the pistil includes the stigma, which receives the pollen, and the ovary, where seeds develop. This arrangement allows a single flower to potentially pollinate itself, though many species encourage cross-pollination with other trees. Trees like apple, cherry, plum, and magnolia feature these combined structures, meaning every flower has the capacity to develop into fruit.
Trees with Separate Sexes on One Plant
Many common trees separate their male and female parts into distinct, single-sex flowers housed on the same individual plant. These trees are classified as monoecious, a term that translates to “one house” in Greek, reflecting the presence of both sexes on a single body. Male flowers (staminate) are designed solely to produce and release pollen, while female flowers (pistillate) contain the structures necessary for seed development and fruit production. Trees like birch, pine, and walnut produce separate male and female reproductive cones or flowers on the same tree. This separation promotes outcrossing, or mating with another tree, often by positioning male flowers lower or having them bloom at a slightly different time to minimize self-pollination.
Truly Male or Female Trees
Only a distinct minority of tree species conform to the simple binary of being entirely male or entirely female, a reproductive strategy called dioecious. An individual tree will produce only one type of flower for its entire life. A male tree produces staminate flowers, releasing pollen but never developing fruit or seed. Conversely, a female tree produces pistillate flowers, which must receive pollen from a separate male tree to produce viable seeds. Examples include the iconic ginkgo, holly, and the box elder maple. For a female holly tree to produce the berries prized in winter landscaping, a male holly of the correct species must be planted within a reasonable distance for successful pollination.
Why Tree Sex Is Important for Landscaping
Understanding a tree’s sexual strategy is relevant to urban planning and residential planting for two primary reasons: the mess from fruit and the impact of pollen on air quality. Only female trees, or species with perfect flowers, produce the seeds, fruits, or nuts that can drop and create a maintenance issue on sidewalks, patios, and lawns. For instance, the female ginkgo tree produces an apricot-like seed that is notorious for its foul, rancid odor when it ripens and drops to the ground. This mess is why nurseries and city planners historically favored planting clones of male ginkgo trees, which are fruitless and tidy.
This preference for “fruitless” male trees, however, inadvertently created a significant issue for allergy sufferers, a phenomenon sometimes called “botanical sexism.” Only male trees and male flowers produce the vast quantities of light, airborne pollen responsible for seasonal allergies. When entire city blocks or new developments are planted predominantly with male trees—such as male clones of ash, maple, or mulberry—the concentration of allergenic pollen in the air rises dramatically. Selecting female clones or trees with perfect flowers, which rely on insects for pollination and produce little to no airborne pollen, can substantially reduce local pollen counts and improve air quality for sensitive populations.