CATKIN

'Catkins', or 'aments', are slim, cylindrical flower clusters, wind-pollinated (anemophilous) and without petals, that can be found in many plant families, including Betulaceae, Fagaceae, Moraceae, 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.
Oak, birch, hazel, willow, alder, hickory, chestnut, sweetfern, poplar, and mulberry are catkin-bearing.