This name is a synonym of Callitriche terrestris subsp. subsessilis (Fassett) Bacig..
The record derives from WCSP
(data supplied on 2012-03-23)
which reports it as a synonym (record 31570) with original publication details: Rhodora 53: 150 1951.
Full publication details for this name can be found in IPNI: http://ipni.org/urn:lsid:ipni.org:names:42494-2.
This name was in version 1 of The Plant List, record kew-31570, and has not been changed.