Onion genus (6)
I believe the answer is:
allium
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">onion genus</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 allium that I've seen before include "Plant of onion genus" , "Plant of onion family" , "Bulbous plant" , "Onion/garlic genus" .)