  We analyse the clustering of cosmic large scale structure using a consistent
modified gravity perturbation theory, accounting for anisotropic effects along
and transverse to the line of sight. The growth factor has a particular scale
dependence in f(R) gravity and we fit for the shape parameter f_{R0}
simultaneously with the distance and the large scale (general relativity) limit
of the growth function. Using more than 690,000 galaxies in the Baryon
Oscillation Spectroscopy Survey Data Release 11, we find no evidence for extra
scale dependence, with the 95\% confidence upper limit |f_{R0}| <8 \times
10^{-4}. Future clustering data, such as from the Dark Energy Spectroscopic
Instrument, can use this consistent methodology to impose tighter constraints.
