Trees with catkins (6)
I believe the answer is:
alders
'trees with catkins' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for alders that I've seen before include "Trees of the birch family" , "Trees with toothed leaves" , "Trees for red Sal" , "Catkin-bearing trees" , "Al's red trees, strangely" .)