Hymenophyllaceae represents a very ancient lineage of ferns that inhabit hyperhumid places and appeared in the Early Cretaceous, prior to the breakup of Gondwana; these features make Hymenophyllaceae especially useful to establish biogeographic patterns. The diversity of Hymenophyllaceae in meridional Yungas and their biogeographical relationships, employing a panbiogeographic analysis, are discussed. Nine species in four genera: Crepidomanes, Didymoglossum, Hymenophyllum and Polyphlebium were found; Crepidomanes pyxidiferum constitutes a novelty of generic level for Argentina. A key to all genera of Hymenophyllaceae present in Argentina are provided as well as keys for all species inhabiting the Yungas, which are also described and illustrated. The generalized track shows close relationships among the Argentine Yungas with the North Andes and the Parana dominion, overcoming the arid barrier represented by the Chacoan dominion. Furthermore, the South American Transition Zone constitutes a current barrier between the neotropical and the south-andean Hymenophyllaceae pteridofloras.
Crepidomanes; Dydimoglossum; Hymenophyllum; Polyphlebium; biogeography
