Brown seaweed (4)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">brown seaweed</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for kelp that I've seen before include "Large brown seaweed used for manure" , "Type of seaweed" , "Large brown leathery seaweed" , "Coarse brown seaweed" , "Brown seaweed with fluted leathery fronds" .)