catkin

A crowded group of single-sex flowers arranged on an axis (spike), often in the form of furry tufts as in the pussy willows (eg. grey willow, goat willow), or elongating to become pendulous as in hazel. Catkins are conspicuous in late winter or early spring before any deciduous tree has come into leaf.

This definition is abridged from A – Z of tree terms: A companion to British arboriculture.
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