The subcosmopolitan fern genus Hymenophyllum s.l. (Hymenophyllaceae) includes more than 300 species, mostly in tropical areas. Phylogenetic studies using both morphology and molecules were performed in order to clarify the still controversial systematics of this group. Previous works using rbcL sequences have suggested that this genus, in a broad sense, may be monophyletic, but these same studies also show a lack of resolution at the infrageneric level. This contrasts with substantial resolution in the sister genus Trichomanes. Another marker, the chloroplast rps4 gene, has thus been tested. Sequences were acquired for 25 species, representing the 9 major groups of Hymenophyllum, including the monospecific genera Serpyllopsis, Hymenoglossum, and Rosenstockia, as well as the peculiar Microtrichomanes. Five species of Trichomanes plus the monotypic genus Cardiomanes were added as outgroups. Rps4 data provide better resolution than rbcL sequences by distinguishing clearly Morton's subgenera Sphaerocionium, Mecodium, and Hymenophyllum. Moreover, this gene alone and in a combined analysis (rps4 + rbcL) provide new insights into the relationships within Hymenophyllum sensu lato. Conclusions include: 1) the robustly supported inclusion of the problematic monotypic genera in Hymenophyllum s.l., with Microtrichomanes in a basal position and closely related to subg. Sphaerocionium, and Serpyllopsis and Rosenstockia included in subg. Hymenophyllum; and 2) placement of subg. Craspedophyllum and subg. Hemicyatheon within subg. Hymenophyllum. In parallel, and using the same taxonomic sample, a morphological study has been initiated. Despite the paucity of informative characters for identifying natural groups, the phylogenetic trees generated from morphology reveal some relationships within Hymenophyllum s.l. that are consistent with those from molecules. Both approaches are discussed. In addition, the evolution of sorus shape, traditionally considered a diagnostic character in this group, is re-evaluated.

Key words: Hymenophyllaceae, Hymenophyllum, morphology, rbcL, rps4, systematics