In a gale, perhaps, they can't flower (5)
I believe the answer is:
algae
'can't flower' is the definition.
I can't tell whether this defines the answer.
'in a gale perhaps they' is the wordplay.
'in' indicates putting letters inside.
'perhaps' is an anagram indicator.
'they' becomes 'a' (I am not sure about this - if you are sure you should believe this answer much more).
'gale' anagrammed gives 'lgae'.
'lgae' going 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" .)