This name is a synonym of Callitriche truncata subsp. occidentalis (Rouy) Schotsman.
The record derives from WCSP
(data supplied on 2012-03-23)
which reports it as a synonym and as an illegitimate name (record 31643) with original publication details: Index Kew. Suppl. 4: 34 1913.
This name was in version 1 of The Plant List, record kew-31643, and has not been changed.