  We show that the Ree unital $\mathcal{R}(q)$ has an embedding in a projective
plane over a field $F$ if and only if $q=3$ and $\mathbb{F}_8$ is a subfield of
$F$. In this case, the embedding is unique up to projective linear
transformations. Besides elementary calculations, our proof uses the
classification of the maximal subgroups of the simple Ree groups.
