A acorn of <a href="https://en.wikipedia.org/wiki/Quercus_petraea" class="extiw" title="en:Quercus petraea">Quercus petraea</a>.
<a href="//commons.wikimedia.org/wiki/User:T137" title="User:T137">T137</a>
CC BY-SA 3.0
<span class="int-own-work" lang="en">Own work</span>