A revision of the genusCyathorachis in Japan

Cyathorachis, a genus of Cretaceous tree fern rachises is revised. In addition to the type specimens of the sole species,C. fujiiana Ogura, two specimens collected near the type locality were examined histologically. The histological data being used for the taxonomical comparison were obtained from anatomical studies on the rachises of extant tree ferns. As a result of the study three species are recognized, two of which are new. As a result of this study, it appears that species differentiation of the tree ferns in the late Cretaceous age of Hokkaido was rather high, as it is now in tropical and subtropical regions. Contributions from the Laboratory of Phylogenetic Botany, Chiba University, No. 74.