This name is a synonym of Sedum stenopetalum subsp. monanthum (Suksd.) R.T. Clausen.
The record derives from Tropicos
(data supplied on 2012-04-18)
which reports it as a synonym (record 8902003) with original publication details: Biol. Ser. Bull. State Univ. Montana 15: 30 1910.
Full publication details for this name can be found in IPNI: http://ipni.org/urn:lsid:ipni.org:names:231707-2.
This name was in version 1 of The Plant List, record tro-8902003.