It may be spotted in the woods wearing a cap (9)
I believe the answer is:
toadstool
This clue could be a double definition.
'it may be spotted in the woods' is the first definition.
The definition suggests a singular noun which matches the answer.
'a cap' is the second definition.
The answer and definition can be both plants as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'wearing' acts as a link.
Can you help me to learn more?
(Other definitions for toadstool that I've seen before include "Plant akin to mushroom" , "a potentially toxic development" , "Common fungus" , "what's poisonous maybe" , "that could be poisonous" .)