The correct name for Pseuderanthemum lilacinum, P. teijsmannii and P. teysmannii (Acanthaceae) in Peninsular Malaysia

Summary Pseuderanthemum lilacinum Stapf is known from a single specimen collected in 1909 from Batu Caves, a karst limestone hill in Selangor, Peninsular Malaysia. Ridley had drawn attention to similarities between it and P. teijsmanni (C.B.Clarke) Stapf, which grows in lowland forest in Peninsular Malaysia. Examination of a range of specimens shows this conclusion to be correct and P . lilacinum becomes a synonym of P. teijsmannii . Confusion with the names Eranthemum teijsmanni T.Anderson, E. teijsmanni T.Anderson ex C.B.Clarke, Pseuderanthemum teysmanni Ridl., P. teijsmannii (C.B.Clarke) Stapf and Pseuderanthemum teysmannii (Miq.) Ridl. is resolved. Eranthemum teijsmanni T.Anderson is a nomen nudum without a type specimen. Eranthemum teijsmanni T.Anderson ex C.B.Clarke describes a Peninsular Malaysian taxon and is based on a detailed description and citation of specimens. In transferring Peninsular Eranthemum species to Pseuderanthemum , Ridley used the name P. teysmanni Ridl. for Clarke’s species. However, Stapf had already validated the combination in Pseuderanthemum and so this species should correctly be cited as P. teijsmannii (C.B.Clarke) Stapf. It is endemic in Peninsular Malaysia. P. teijsmannii (C.B.Clarke) Stapf and P. teysmannii (Miq.) Ridl. have both been misapplied to Chinese species, which are quite different from the Peninsular species.