This name is a synonym of Carex illota L.H.Bailey.
The record derives from WCSP
(data supplied on 2012-03-23)
which reports it as a synonym (record 225035) with original publication details: Bot. California 2: 233 1880.
This name record (from WCSP) 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 Carex bonplandii in version 1 of The Plant List.