Abstract: The genus Taphrina, founded by Fries in 1832 on the species 'Taphrina populina, is the only recognized genug in the family Taphrinaceae, order Taphrinales of the Ascomycetes.All species of the genus are parasitic on higher plants or ferns, forming mycelium (a) intercellularly ; (b) subcuticularly ; or (c) within the epidermal wall ; forming asci in a subcuticular la5'er or in a wall locule ; overwintering in the form of blastospores derived from ascospores by budding or in a few species as perennial mycelium.Infection (so far as known) is by blastospores.Asci arise from rounded ascogenous cells (chlamydospores), either by elongation of the ascogenous cell or by bursting out from the ascogenous-cell wall.In many species a stalk cell (basal cell) is cut off from the ascus proper.Budding of the ascospores to form blastospores may occur within the ascus and continues after spore expulsion.Mycelium is dicaryotic.Fusion of nuclei occurs in the ascogenous cell; meiosis in the young ascus.In one species (T.epiphylla) conjugation of ascospores (or blastospores) occurs, resulting in dicaryotic hyphae.In other species (so far as known) the dicaryotic condition is attained by division of the single nucleus of the blastospore.Species of Taphrina grow readily in artificial media if cultures are originated from ascospores or blastospores; behaving in media as yeasts.Cells formed in culture are blastospores, hyphae, ascogenous cells, and (rarely) asci.Ninety-eight species of Taphrina are here redescribed and redefined (other species being reduced to synonymy or excluded).Tliese are distributed by hosts as follows: On Ferns, 24 species; on Populus and Salix, 4; on Betulaceae, 23; on Fagaceae, 5; on Ulmaceae, 2; on Rosaceae (except Prunus), 7; on Pmnm, 17; on Rhus, 1; on Acer, 11; on Aesculus, 1; on Sebastiana, 1; on Zingiberaceae, 2.