Red root vegetable (4)
'red root vegetable' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for beet that I've seen before include "The mangelwurzel, for instance" , "Source of food" , "Sugar-yielding plant" , "An edible root plant" , "Root, maybe source of sugar" .)
(Other definitions for beetroot that I've seen before include "salad ingredient" , "Vegetable cooked or used in salads and pickles" , "vegetable's produced" , "plant" , "one to get pickled" .)