Thus, flowers of wind pollinated trees generally have large anthers and stigmas and lack the colorful petals associated with insect pollinated flowers. Pictures of the tree flowers shown below were taken in Kansas in late April. On the left are male catkins that have emerged from a bud. Red anthers that have not yet shed their pollen are visible in the upper half of the catkins. On the right a female catkin is recognizable by flowers with round, green ovaries topped by large, sticky, light yellow stigmas.
Cottonwood trees have only male or female catkins and as a result are said to be dioecious.
On the left the reddish female flowers have two long white stigmas extending from each ovary, while the male flowers consist of little more than a few anthers at the end of long pedicels. Like cottonwood, boxelder produces only female or male flowers on a single tree. Since the male and female flowers are separate, but on the same tree, sweetgum is said to be monoecious.