Roots of perhaps edible annual plant (3)
I believe the answer is:
pea
'plant' is the definition.
(pea is a kind of plant)
'roots of perhaps edible annual' is the wordplay.
'roots of' indicates taking the first letters (I've seen 'root of' mean this).
The initial letters of 'perhaps edible annual' is 'PEA'.
(Other definitions for pea that I've seen before include "Edible seed from pod" , "Cause of a princess's insomnia?" , "Little green vegetable" , "Seed eaten as vegetable" , "Legume" .)