Tree on coast, possibly, or shrub? (11)
I believe the answer is:
cotoneaster
'shrub?' is the definition.
(cotoneaster is a kind of shrub)
'tree on coast possibly' is the wordplay.
'possibly' indicates an anagram.
'tree'+'on'+'coast'='treeoncoast'
'treeoncoast' with letters rearranged gives 'COTONEASTER'.
'or' is the link.
(Other definitions for cotoneaster that I've seen before include "Red-berried garden shrub" , "Plant" , "Shrub with red berries" .)