  We find an unusual anisotropy of the inplane field magnetoresistance in
ultra-high mobility SiGe/Si/SiGe quantum wells. The anisotropy depends on the
orientation between the inplane field, $B_\parallel$, and current, $I$,
relative to the crystallographic axes of the sample and is a consequence of the
intrinsic ridges on the quantum well surface. For the simplest orientations
between current and crystallographic axes, a method of recalculating the
magnetoresistance measured at $I\perp B_\parallel$ into the one measured at
$I\parallel B_\parallel$ is suggested and is shown to yield results that agree
with the experiment.
