The new genus Apotreubia is described to accommodate Treubia nana, which differs too greatly from the four other species currently considered to belong to the genus Treubia to be classified among them. Treubia is a unique genus and the only member of the family Treubiaceae. Schuster (1964) proposed the suborder Treubiineae for this phylogenetically isolated family. At present the genus includes five species: the famous Indonesian Treubia insignis Goeb., T. bracteata Steph. from Samoa and Fiji, T. lacunosa (Col.) Prosk. from New Zealand, T. tasmanica Schust. & Scott (nom. nud.) from Tasmania, and T. nana Hatt. & H. Inoue from Japan and British Columbia. Except for T. nana all of them have large thalli, often 15 cm long and 8-25 mm wide, and are distributed in tropical or antarctic regions; T. nana has far smaller thalli, about 2-3 cm long and 4-6 nrm wide, and occurs in subalpine areas of boreal regions (Fig. 1). Treubia nana was originally described by Hattori and Inoue (1954) from the Chichibu Mountains, central Japan, at about 139?E longitude and 360N latitude, where it occurred on humus-covered rocks, decayed wood, and humus under conifer forests at an elevation of about 2,000 meters, intermingled with or creeping over a mat of Hylocomium splendens, Lepidozia fiamentosa, Mnium speciosum, Pleurozium schreberi, Blepharostoma trichopyllum, and other bryophytes. Kitagawa (1959) found T. nana on Mt. Hayachine, northern Japan (39?30'N, 141?20'E), where it occurred on rocks under a forest dominated by Abies mariesii at about 1,800 meters, associated with Sphagnum sp., Dicranum sp., Rhytidiadelphus calvescens, Scapania bolanderi, Calypogeia neesiana, and Lepidozia filamentosa. The third and disjunctive locality was reported in British Columbia. Schofield (1962) recorded it from Chaatl Island, Queen Charlotte Islands . . . on earth of upturned stump in coniferous forest near sea level; the common bryophytes among which it grew were Bazzania tricrenata, Mylia taylori, Mnium glabrescens, Herberta adunca, Scapania bolanderi, Macrodiplophylltm plicatum, Dicranum scoparium, and Microlepidozia makinoana. 1 Acknowledgement is made of the partial financial support of this project through grants from the Japan Society for the Promotion of Science and the National Science Foundation as part of the Japan-U.S. Cooperative Science Program. The Department of Geography, University of Chicago, granted permission to use Goode Base Map No. 101HC. 2 Contribution from the Hattori Botanical Laboratory and Contribution No. 251 (new series) from the Botanical Laboratory, University of Ten-