  We investigate structure formation for ultralight scalar field dark matter
coupled to quintessence, in particular the cosmon-bolon system. The linear
power spectrum is computed by a numerical solution of the coupled field
equations. We infer the substructure abundance within a Milky Way-like halo.
Estimates of dark halo abundances from recent galaxy surveys imply a lower
bound on the bolon mass of about $9 \times 10^{-22}$ eV. This seems to exclude
a possible detection of scalar field dark matter through time variation in
pulsar timing signals in the near future.
