\begin{tikzpicture}
% légende
\node[fill,forest]   (forest) [label=right:forêt]   at (0,1.5) {};
\node[fill,fire]  (fire)   [label=right:feu]     at (0,1  ) {};
\node[fill,ashes]  (ash)    [label=right:cendre]      at (0,0.5) {};
\node[fill,gray!60]    (generic)[label=right:quelconque]      at (0,0  ) {};
\end{tikzpicture}