Seabird circling key tropical plant (4,4)
I believe the answer is:
tree fern
'tropical plant' is the definition.
(I've seen this before)
'seabird circling key' is the wordplay.
'seabird' becomes 'tern' (tern is a kind of seabird).
'circling' is an insertion indicator (circling can mean going around or containing).
'key' becomes 'reef' (I've seen this before).
'tern' placed around 'reef' is 'TREE-FERN'.
(Other definitions for tree fern that I've seen before include "Palm-like plant" , "Tall plant" , "tropical plant" .)