An expanded M1 plant (7)
I believe the answer is:
anemone
'plant' is the definition.
(anemone is a kind of plant)
'an expanded m1' is the wordplay.
I cannot really understand how this works, but
'an' could be 'one' and 'one' is found in the answer.
'm1' could be 'm' and 'm' is found within the answer.
The remaining letters 'ane' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for anemone that I've seen before include "Tentacled sea dweller, flower" , "Flower; marine polyp" , "Woodland plant, eg the windflower" , "Sea creature, also flower" , "bloom" .)