  As a highly frustrated model Hamiltonian with an exact dimer ground state,
the Heisenberg antiferromagnet on the maple leaf lattice is of high theoretical
interest, and a material realization is intensely sought after. We determine
the magnetic Hamiltonian of the copper mineral bluebellite using density
functional theory based energy mapping. As a consequence of the significant
distortion of the spin $S=1/2$ maple leaf lattice, we find two of the five
distinct nearest neighbor couplings to be ferromagnetic. Solution of this
Hamiltonian with density matrix renormalization group calculations points us to
the surprising insight that this particular imperfect maple leaf lattice, due
to the strongly ferromagnetic Cu$^{2+}$ dimer, realizes an effective $S=1$
breathing kagome Hamiltonian. In fact, this is another highly interesting
Hamiltonian which has rarely been realized in materials. Analysis of the
effective model within a bond-operator formalism allows us to identify a
valence bond solid ground state and to extract thermodynamic quantities using a
low-energy bosonic mean-field theory. We resolve the puzzle of the apparent
one-dimensional character of bluebellite as our calculated specific heat has a
Bonner-Fisher-like shape, in good agreement with experiment.
