This name is a synonym of Diphasiastrum tristachyum (Pursh) Holub.
The record derives from Tropicos
(data supplied on 2012-04-18)
which reports it as a synonym (record 26605058) with original publication details: Fl. Bor.-Amer. 2: 267 1840.
Full publication details for this name can be found in IPNI: http://ipni.org/urn:lsid:ipni.org:names:147258-2.
This name was in version 1 of The Plant List, record tro-26605058, and has not been changed.