  We introduce a decorated configuration space $\mathscr{C}\!{\rm
onf}_n^\times(a)$ with a potential function $\mathcal{W}$. We prove the cluster
duality conjecture of Fock-Goncharov for Grassmannians, that is, the
tropicalization of $\big(\mathscr{C}\!{\rm onf}_n^\times(a), \mathcal{W}\big)$
canonically parametrizes a linear basis of the homogeneous coordinate ring of
the Grassmannian $\operatorname{Gr}_a(n)$ with respect to the Pl\"ucker
embedding. We prove that $\big(\mathscr{C}\!{\rm onf}_n^\times(a),
\mathcal{W}\big)$ is equivalent to the mirror Landau-Ginzburg model of the
Grassmannian considered by Eguchi-Hori-Xiong, Marsh-Rietsch and
Rietsch-Williams. As an application, we show a cyclic sieving phenomenon
involving plane partitions under a sequence of piecewise-linear toggles.
