Abstract
The genus Plagiomnium T.J. Kop. is revised for Argentina, based on examination of herbarium specimens and on specimens collected during three field expeditions (2005-07). The following species are recognized for the Argentinean Bryological Flora: Plagiomnium undulatum (Hedw.) T.J. Kop., P. ellipticum (Brid.) T.J. Kop., and P. rhynchophorum (Hook.) T.J. Kop. This last taxon is a new record for the bryological flora of Argentina. All the specimens revised and previously identified as Plagiomnium rostratum (Schrad.) T.J. Kop. or their synonyms have been re-identified as P. rhynchophorum. Thus, we suspect that P. rostratum does not occur in Argentina. We suggest, before excluding this taxon from the Checklist of Mosses of Argentina, that the genus should be revised. The threats to Plagiomnium populations in Argentina are analyzed. Identification keys, descriptions, iconography, and distribution maps for all the species are provided.