Family- and genus-level circumscription of ferns in the suborder Aspleniineae (eupolypods II) has long been controversial, due in part to confusion about the relationship among the families Aspleniaceae and Athyriaceae. Recent studies have demonstrated that character states traditionally used to infer a close relationship between these two families are either symplesiomorphic or homoplastic, and re-examination of numerous taxa has led to the recircumscription of several clades, and the description of several new families and genera. In light of these findings, we re-evaluated the taxonomic affinities of Diplazium praestans, a little-known fern from western Amazonia that is morphologically disparate to the remainder of Neotropical Diplazium. Using sequence data from three chloroplast markers and analysis of eight morphological characters, we demonstrate that Diplazium praestans was erroneously placed in that genus and instead is a Hymenasplenium. We place it in a phylogenetic context, reassess its morphology in light of our findings, evaluate its conservation status under IUCN criteria, and provide a new combination: Hymenasplenium praestans. We also provide an updated key to the Neotropical species of Hymenasplenium and discuss unresolved taxonomic problems in the genus.