This name is a synonym of Lemna obscura (Austin) Daubs.
The record derives from WCSP
(data supplied on 2012-03-23)
which reports it as a synonym (record 452249) with original publication details: Lemnac. 144 1868.
This name record (from WCSP) was not included in version 1 of The Plant List. It is possible the same name was included from a different data source, to check this you can search for Lemna minor in version 1 of The Plant List.