A revision of the genusCeratopteris is presented based on comparative morphology and geographical distribution. Four species are recognized:C. thalictroides, C. cornuta, C. pteridoides, andC. richardii. Characteristics of taxonomic importance include frond length, shape, and dissection; stipe width; insertion of basal pinnae; bud development; habit; annulus cell number; spore number per sporangium; spore size; and spore surface features. Evolution within species and putative hybridization between species are discussed.