In the scope of pantropical studies aimed at understanding how the diversity of grammitid ferns (Polypodiaceae) has evolved and is maintained, we studied a diverse grammitid community in treeline elfin forests in eight study plots of 400 m2 each at 3200 m on Cerro Toledo, Loja, southern Ecuador. We recorded a total of 7986 individuals of 16 grammitid species. Ascogrammitis lehnertii is here described as a new species. We also recorded Mycopteris leucosticta, a species previously believed to be restricted to the Chocó region of Ecuador. We found that the grammitid species were segregated by habitat into trunk-base and trunk specialists, which suggests that species coexistence in these diverse epiphytic communities is at least partly linked to habitat segregation. Ascogrammitis lehnertii and M. leucosticta were the second and third most abundant species, respectively, and both were mostly trunk-base species. The new species A. lehnertii differs from its congeners by the combination of its relatively broad lamina, (2‐)3‐4 cm wide, fertile leaves bearing 2 mm long reddish setae in and near the sori, and by bearing proliferous roots from which new plants emerge. Phylogenetic analyses of atpß, rbcL, rps4, trnG-trnR, and trnL-trnF DNA molecular sequences, using maximum likelihood, place A. lehnertii as sister to A. cuencana with strong support. Despite previous intensive collection efforts in Loja for the past 30 yr, all but one of the collections of this new species were made in the last three years. The discovery of A. lehnertii and the new record of M. leucosticta highlight the patchy distribution of some species in the Andes and the value of surveying habitats that potentially host unrecognized plant diversity. In order to facilitate further discovery, we provide a key to all species of Ascogrammitis.