Inspiration from what's concealed by seaside alders (4)
I believe the answer is:
idea
'inspiration' is the definition.
(I've seen this before)
'what's concealed by seaside alders' is the wordplay.
'what's concealed' says the answer is hidden in the clue.
'IDEA' is hidden within 'by seaside alders'.
'from' is the link.
(Other definitions for idea that I've seen before include "Suggestion" , "Plan" , "Thought; concept" , "Fancy" , "Notion, image" .)