This name is a synonym of Euphorbia bifida Hook. & Arn..
The record derives from Tropicos
(data supplied on 2012-04-18)
which reports it as a synonym (record 50105983) with original publication details: J. Fac. Sci. Univ. Tokyo, Sect. 3, Bot. 6(6): 283, f. 34 1954.
This name record (from Tropicos) 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 Chamaesyce vachellii in version 1 of The Plant List.