For a tree to bear fruit, its flowers must be pollinated. Some fruit trees have flowers that can pollinate themselves. Others have separate male and female flowers, while some have only male or only female flowers.
Pollination occurs when pollen from the male part of a flower transfers to the female part of a flower. Some flowers, called "perfect flowers," contain both male and female parts. Other flowers are exclusively male or exclusively female.
Some fruit trees, called "self-fruitful," contain perfect flowers that can produce fruit from their own pollen. "Self-unfruitful" trees, on the other hand, contain perfect flowers that are unable to pollinate themselves. Other trees, called "monoecious," contain separate male and female flowers on the same tree. "Dioecious" trees contain only male flowers or only female flowers.
To tell whether a fruit tree is male or female, check to see if it has fruit. If it does, it must be female. A fruitless tree is not necessarily male, however. It could simply be a female tree that has not been pollinated.