This name is a synonym of Lactuca singularis Wilmott.
The record derives from TICA
(data supplied on 2012-02-11)
which reports it as a synonym (record 1861EA20-3B57-4DAE-88D6-CF77771C2A74) with original publication details: 237 1981.
This name was in version 1 of The Plant List, record gcc-66529, and has not been changed.