Plesioneurott, originally published as a subgenus of Mesophlebion, is here raised to generic rank. New descriptions of both genera are provided, keys to all known species, and synonymy and description for each. Synonymy is reduced to basionyms except where other synonyms refer to important literature; in all cases published combinations in Thelypteris are recorded. Type material of all basionyms has been examined. An index of new names and of all basionyms cited is provided. Mesophlebion, as here arranged, is confined to Malesia (with a short extension northwards from Malaya) with Borneo as centre of distribution. It comprises 18 species, of which the following are new: M. dulitense, M. caroli, M. rufescens, and M. arenicola. The following basionyms are reduced to synonymy: Dryopteris paleata Copel., D. divergens Rosenst., D. subdimorpha Copel., Aspidium latum Mett., Syngramma angusta Copel. Mesophlebion is perhaps most nearly related to Cyclosorus sensu Holttum 1971. Plesioneuron is distributed mainly in New Guinea and the Pacific, with one species in North Borneo, two in the Moluccas, and two in the Philippines. It comprises 39 species, of which the following are here described as new: P. ctenolobum, P. doctersii, P. dryas, P. fuchsii, P. kundipense, P. platylobum, P. pullei, P. royenii, P. rigidilobum, P. subglabrum, P. subterminale, P. tahitense, P. translucens; also a new variety P. hopeanum (Bak.) Holttum var. acutilobum. The following basionyms are reduced to synonymy: Lastrea varievestita Copel., Dryopteris hunsteiniana Brause, D. ensipinna Brause, D. quadriaurita Copel., D. schlechteri Brause, D. schizophylla v.A.v.R., Aspidium brackenridgei Mett., Nephrodium inaequilaterale Baker. Plesioneuron appears to be most nearly related to Chingia Holttum.