A male catkin on a willow

Catkins, or aments, are slim, cylindrical flower clusters, wind-pollinated and without petals, that can be found in many plant families, including Betulaceae, Corylaceae, Fagaceae and Salicaceae. They contain unisexual flowers. Often one plant has only male catkins, while another has female, but it is also possible for a plant to contain both male and female catkins.