Epiphytic or usually terrestrial ferns with a short fleshy rhizome bearing only one or a few, mostly fleshy, leaves, these erect, petiolate, continuous with the rhizome, the lamina usually divided into a sterile and a stalked fertile portion; veins free or reticulate. Sporangia with a wall composed of several layers of cells, opening with a slit, containing numerous trilete thick-walled subspherical spores of one kind. Four genera, two monotypic, the others with about 60 species of almost world-wide distribution.