Waterside plants (5)
I believe the answer is:
reeds
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">waterside plants</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 reeds that I've seen before include "Tall stiff marsh grasses" , "Water plants" , "Waterside plants" , "Stops" , "Tall grasses with hollow stems" .)