Acorn producers (4)
I believe the answer is:
oaks
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">acorn producers</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 oaks that I've seen before include "Trees of the genus Quercus" , "Epsom Classic race" , "Acorn trees" , "Acorn producers" , "Mighty ones from little acorns grow" .)