This name is a synonym of Ornithogalum graminifolium Sessé & Moc..
The record derives from Tropicos
(data supplied on 2012-04-18)
which reports it as a synonym (record 18402966).
This name record (from Tropicos) 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 Ornithogalum attenuatum in version 1 of The Plant List.