Underground root's original potato maybe (5)
I believe the answer is:
tuber
'potato maybe' is the definition.
(I've seen this before)
'underground root's original' is the wordplay.
'underground' becomes 'tube' ('tube' can be a synonym of 'underground').
'original' says to take the initial letters.
The initial letter of 'roots' is 'r'.
'tube'+'r'='TUBER'
(Other definitions for tuber that I've seen before include "Fleshy underground root" , "Thickened underground stem" , "Fleshy root, vegetable say" , "or still vegetating?" , "Root of potato etc" .)