  We demonstrate that rotation symmetry is not a necessary requirement for the
existence of fractional corner charges in Cn-symmetric higher-order topological
crystalline insulators. Instead, it is sufficient to have a latent rotation
symmetry, which may be revealed upon performing an isospectral reduction on the
system. We introduce the concept of a filling anomaly for latent crystalline
symmetric systems, and propose modified topological invariants. The notion of
higher- order topology in two dimensions protected by Cn symmetry is thus
generalized to a protection by latent symmetry. Our claims are corroborated by
concrete examples of models that show non-trivial corner charge in the absence
of Cn-symmetry. This work extends the classification of topological crystalline
insulators to include latent symmetries.
