First part of plant consumed by land turtle (8)
I believe the answer is:
terrapin
'turtle' is the definition.
(terrapin is a kind of turtle)
'first part of plant consumed by land' is the wordplay.
'first part of' indicates taking the first letters.
'consumed by' indicates putting letters inside.
'land' becomes 'terrain' (I've seen this before**).
The first letter of 'plant' is 'p'.
'p' placed into 'terrain' is 'TERRAPIN'.
(Other definitions for terrapin that I've seen before include "Partner I found for freshwater tortoise" , "freshwater creature" , "A reptile; a printer (anag.)" , "Little turtle" , "temporary building" .)