Tall prickly plant (6)
I believe the answer is:
teasel
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">tall prickly plant</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 teasel that I've seen before include "Plant with spiny purple flower heads" , "Plant with prickly flower head" , "Prickly plant (S, not Z)" , "Eel sat up on the plant" , "it helps us to nap" .)