  We report zero field muon spin relaxation (muSR) measurements on RFeAsO with
R = La, Ce, Pr, and Sm. We study the interaction of the FeAs and R (rare earth)
electronic systems in the non superconducting magnetically ordered parent
compounds of RFeAsO{1-x}Fx superconductors via a detailed comparison of the
local hyperfine fields at the muon site with available Moessbauer spectroscopy
and neutron scattering data. These studies provide microscopic evidence of long
range commensurate magnetic Fe order with the Fe moments not varying by more
than 15 % within the series RFeAsO with R = La, Ce, Pr, and Sm. At low
temperatures, long range R magnetic order is also observed. Different combined
Fe and R magnetic structures are proposed for all compounds using the muon site
in the crystal structure obtained by electronic potential calculations. Our
data point to a strong effect of R order on the iron subsystem in the case of
different symmetry of Fe and R order parameters resulting in a Fe spin
reorientation in the R ordered phase in PrFeAsO. Our symmetry analysis proves
the absence of collinear Fe--R Heisenberg interactions in RFeAsO. A strong
Fe--Ce coupling due to non--Heisenberg anisotropic exchange is found in CeFeAsO
which results in a large staggered Ce magnetization induced by the magnetically
ordered Fe sublattice far above T_N{Ce}. Finally, we argue that the magnetic
R--Fe interaction is probably not crucial for the observed enhanced
superconductivity in RFeAsO{1-x}Fx with a magnetic R ion.
