AbstractNorth American members of the genus Plateumaris Thomson, 1859, are revised; 17 species are recognized and 23 taxonomic changes are made in their classification. Plateumaris balli and P. schaefferi are described as new species. Names elevated from subspecies to species rank are P. robusta (Schaeffer) and P. frosti (Schaeffer); P. aurifera (LeConte) is revalidated, removed from junior synonymy with P. wallisi (Schaeffer); Donacia idola Hatch is considered a junior subjective synonym of P. dubia (Schaeffer); D. pyritosa LeConte is considered a junior subjective synonym of P. pusilla (Say); an altered species concept is transferred to P. flavipes (Kirby), with D. wallisi Schaeffer as a new junior subjective synonym, and P. flavipes of authors is correctly named P. shoemakeri (Schaeffer); D. longicollis Schaeffer and D. vermiculata Schaeffer are considered new junior subjective synonyms of P. neomexicana (Schaeffer); D. flavipennis Mannerheim is considered a junior subjective synonym of P. germari (Mannerheim); D. rufa Say (not D. rufa of authors) is transferred to Plateumaris from Donacia, with an altered species concept applied to it, and D. affinis Kirby, D. sulcicollis Lacordaire, D. chalcea Lacordaire, D. kirbyi Lacordaire, and D. jucunda LeConte are considered new junior subjective synonyms of P. rufa (Say). The taxon previously considered D. nitida Germar (sensu Schaeffer) is redescribed as P. schaefferi; P. nitida (Germar) is a valid, different species, with D. emarginata Kirby, D. juncina Couper, and D. pacifica Schaeffer considered new junior subjective synonyms of P. nitida. Neotypes are designated for Donacia pusilla Say, Donacia rufa Say, Donacia metallica Ahrens and Donacia nana Melsheimer; lectotypes are designated for all other names, where necessary.Among Palaearctic taxa, Plateumaris morimotoi Kimoto and P. hirashimai Kimoto are considered new junior subjective synonyms of P. weisei Duvivier, and P. sachalinensis Medvedev, P. orientalis Shavrov and Donacia mongolica Semenov are considered probable junior subjective synonyms of P. weisei; P. sulcifrons Weise and P. affinis (Kunze) and its synonyms are considered new junior subjective synonyms of P. rustica (Kunze); P. caucasica Zaitsev is considered a probable junior subjective synonym of P. roscida Weise; P. discolor (Panzer) (and its synonyms) and P. lacordairii (Perris) are considered junior subjective synonyms of P. sericea (L.); new P. obsoleta Jacobson and P. socia Chen are considered probable junior subjective synonyms of P. sericea.Based on phylogenetic analysis, five species groups are recognized, the P. braccata group (two species), P. rufa group (five species), P. pusilla group (eight species), P. shoemakeri group (four species), and P. nitida group (seven species). The current subgeneric classification of Plateumaris is rejected. Characters hitherto used for subgenera of Plateumaris are shown to be either plesiomorphic or widely distributed among unrelated taxa; the relatively minor structural differences do not merit use of a subgeneric classification. Juliusina Reitter is a junior objective synonym of Plateumaris Thomson.Based on fossil and chorological data, the geographic history of donaciines in general and of Plateumaris in particular is deduced to be so old as to obscure correlations of more recent phylogenetic divergences with specific geologic events. The geographic history of even the most highly derived donaciine groups extends well into the Cretaceous. Therefore, explanations are speculative beyond the generality that donaciines have a long geologic history.
II. Studies in the morphology of spore-producing members.—No. IV. The leptosporangiate ferns
