My neighbor says his Deodar cedar tree is bisexual, and it’s the male cones that are making so much pollen this October. He seemed to be saying this was unusual, and that not all cedar trees were like this, with both male and female cones. What’s the story?
Cedrus deodara is monoecious, which means that an individual tree will bear separate and unisexual male and female flowers. If the tree had bisexual flowers, each flower would be ‘complete’ and ‘perfect,’ that is, with male stamens and female pistil in each flower. So it’s clearer to call the tree monoecious than to say it is bisexual. According to Wayne’s Word: An Online Textbook of Natural History, “about 90 percent of all flowering plants have bisexual flowers with both male (stamen) and female (pistil) sex organs. The remaining 10 percent have unisexual male and female flowers on the same plant (monoecious species) or male and female flowers on separate plants (dioecious species).”
Most conifers (like true cedar) are monoecious. The male pollen cones are 2 to 3 inches long by October, and are found in great number on the lower parts of the tree. Female flowers are tiny, and usually found high up in the tree. Female seed cones take two years to mature. You might wonder how pollination can take place if the female flowers are up high and the pollen is down low. Conifer pollen is wind-dispersed, so it might seem arduous for it to reach the female flowers up above. However, if you consider the geographic origins of the true cedars, you will notice that Deodar cedar is also called Himalayan cedar and like the cedar of Lebanon (C. libani) and the Atlas cedar (C. atlantica), its native range is mountainous. Imagine cedars growing on a sloping mountainside, and you can easily picture the pollen drifting downward to female flowers on the trees below.