Hazel catkins. Hazel (Corylus sp.) is monoecious, meaning it has separate male and female flowers on the same tree. The pendulous catkins are clusters of male flowers. In spring they release pollen, the male reproductive cells of the plant. Two female flowers are visible, one at left and one at right. They are similar to buds, but sprout red stigmas, the female pollen receptors. Stigmas are visible on the left flower. Hazel flowers between January and March.