Salicaceae or the willow family (although they contain more than just the willow genus, Salix) are a family of flowering plants. Recent genetic studies summarized by the Angiosperm Phylogeny Group has greatly expanded the circumscription of the family to contain 55 genera.
In the Cronquist system, the Salicaceae were treated in their own order Salicales, and contained only three genera (Salix, Populus and Chosenia), but APG includes it in Malpighiales. The additional genera were previously treated in Flacourtiaceae, but had a mixed history before that and have been treated in Bembiciaceae, Caseariaceae, Homaliaceae, Poliothyrsidaceae, Prockiaceae, Samydaceae, and Scyphostegiaceae. The Samydaceae (including Caseariaceae) appear rather distinct and might be a valid family however.
Gerrardina is now considered the sole genus of a separate family, Gerrardinaceae.
A catkin or ament is a slim, cylindrical flower cluster, with inconspicuous or no petals, usually wind-pollinated (anemophilous) but sometimes insect pollinated (as in Salix). They contain many, usually unisexual flowers, arranged closely along a central stem which is often drooping. They are 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 it is now believed that this flower arrangement has arisen independently by convergent evolution on a number of occasions.
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.