During a survey of the diatoms present in aerophilic microhabitats associated with waterfalls in Misiones Province (Argentina), mainly within Iguazú National Park (N.P.), seventeen taxa belonging to the genus Humidophila have been recorded. Previously, only six species of the genus have been reported for all of Argentina. Of the seventeen taxa considered here, four exhibit a unique combination of features and are proposed as new species. These are H. iguazuensis sp. nov., H. lagartiensis sp. nov., H. misionera sp. nov. and H. sebastianii sp. nov. An additional six previously-described species (H. arcuatoides, H. contenta, H. nienta, H. parallela, H. platensis and H. subtropica) are reported. Of these previously-described taxa, only H. contenta has been reported previously from Argentina, so the occurrences of the others in the region expand their known geographic distributions. One taxon has been tentatively identified (as Humidophila aff. biscutella) and the remaining six taxa observed are presumed to be new but remain unidentified at the species level because they occurred in small numbers and could not be sufficiently documented for formal description. This is currently the largest concentration of Humidophila taxa reported in a relatively small geographic region anywhere in the world. Morphological features among the species of the genus are discussed, and we describe the structure of the features associated with longitudinal tubes in the genus. We also present and describe the ecological and biogeographic distributions of Humidophila species.