In a gale, perhaps, they can't flower (5)
I believe the answer is:
algae
'can't flower' is the definition.
I can't judge whether this definition defines the answer.
'in a gale perhaps they' is the wordplay.
'in' means one lot of letters goes inside another.
'perhaps' indicates an anagram.
'they' becomes 'a' (I can't explain this - if you can you should give a lot more credence to this answer).
'gale' anagrammed gives 'lgae'.
'lgae' placed around 'a' is 'ALGAE'.
Can you help me to learn more?
(Other definitions for algae that I've seen before include "Simple organisms, e.g. seaweeds" , "Marine growths" , "Aquatic growths" , "They grow near water and don't have ordinary roots or leaves" , "Plants like seaweed" .)