Definition: Dioecious trees are those trees where individual members are usually of a single sex (the word deriving from the Greek for "two households"). Dioecious trees have male (staminate) flowers on one plant and and female (pistillate) flowers on another plant. A single dioecious tree has distinctly female or male reproductive parts. Interestingly, the majority of animal species are dioecious but in tree sexuality, there are many monoecious species.

Examples: A tree that is considered only a male or female is considered to be dioecious. The most common dioecious tree species are ashes, holly, mulberry and ginkgo.