Tree seen in London area (6)
I believe the answer is:
poplar
I believe this clue is a double definition.
'tree' is the first definition.
(poplar tree is a kind of tree)
'london area' is the second definition.
(I've seen this before)
'seen in' is the link.
(Other definitions for poplar that I've seen before include "Tree, maybe from Lombardy" , "Tall, slender tree" , "The tree that quivers" , "Tall tree of north temperate regions" , "tree found mostly in the northern hemisphere" .)