This name is a synonym of Sphaerostigma campestre var. mixtum (H. Lév.) A. Nelson.
The record derives from Tropicos
(data supplied on 2012-04-18)
which reports it as a synonym (record 50082549) with original publication details: Monogr. Onothera 180 1905.
This name was in version 1 of The Plant List, record tro-50082549.