Here is yet another tree with male and female flowers on separate trees. The very common flower shape in nature of style (female) and stamens (male) in the same flower is bisexual or hermaphroditic. Some plants have single sex flowers, but on the same plant; even in the same flowerhead, like some Euphorbia or Asteraceae species. Some species even have both single and dual sex flowers on the same plant.
Some South African trees (and other plants) are similar to Heteropyxis natalensis, the sexes on separate trees. In the flowers of the Heteropyxis genus the female flowers still have staminodes (rudimentary, sterile or abortive stamens, the male flower component) and the male ones have pistillodes (a sterile, vestigial pistil or female part remaining in a staminate or male flower).
Botany has much to do with plant reproductive equipment and process, a big theme in evolution of species (Wikipedia; Coates Palgrave, 2002).