This name is a synonym of Rosa caesia Sm..
The record derives from RJP
(data supplied on 2011-10-18)
which reports it as a synonym (record 11210) with original publication details: ; 1886 80 1886.
This name record (from RJP) was not included in version 1 of The Plant List. It is possible the same name was included from a different data source, to check this you can search for Rosa kerneri in version 1 of The Plant List.