This floristic investigation was made on the mosses growing inside of a collapsed lava tube at Fuji-Fuketsu, 1120m above sea level on NE slope of Mt. Fuji. The dimensions of the site investigated are approximately 17 x 17 m^2 and 6m in depth. This distinctive habitat was formed from 1000-year old lava from the 864 A.D. flow of Mt. Nagao, parasitic volcano of Mt. Fuji. From this small site, 32 species, one subspecies and five varieties of mosses were collected and identified. Among the mosses found were taxa phytogeographically interesting because they were found at a lower elevation than is usual in central Japan. These taxa are Cynodontium gracilescens, Hypnum cupressiforme, Plagiothecium neckeroideum and Rhizomnium nudum. Their presence shows the effect of cool air currents arising from the lava tube. In addition, Bryoerythrophyllum recurvirostre var. robustum was found on the underlying (below the Aokigahara lava flows) calcareous "Lower Misaka Series" soil of Miocene origin.
