Fleshy underground stem (5)
I believe the answer is:
tuber
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">fleshy underground stem</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for tuber that I've seen before include "Fleshy underground root" , "Brute (anag)" , "Fleshy underground part of a stem, often used as food" , "Root eg of potato" , "Thickened underground stem" .)