Catkins, or aments, are slim, cylindrical flower clusters, wind-pollinated except Salix which is insect pollinated(anemophilous) and with inconspicuous or no petals. They contain many unisexual flowers, arranged closely along a central stem which is often drooping. They can be found in many plant families, including Betulaceae, Fagaceae, Moraceae, and Salicaceae. For some time, they were believed to be a key synapomorphy among the proposed Hamamelididae, but they are actually convergent instead.
In many of these plants only the male flowers form catkins, and the female flowers are single (hazel, oak), a cone (alder) or other types (mulberry). In other plants (such as poplar) both male and female flowers are borne in catkins.
