Summary Chara altaica A. Braun (Charales, Charophyceae), a monoecious species of the section Desvauxia, was newly found in Japan and studied by light and scanning electron microscopy (SEM) as well as gene sequence analysis of the large subunit of Rubisco (rbcL). Our first SEM observations of C. altaica oospores revealed that small papillae were scattered on the fossa wall, an SEM oospore wall ornamentation that is essentially different from that of the monoecious species C. (sect. Desvauxia) evoluta T. F. Allen. Phylogenetic analysis demonstrated that C. altaica and 10 European samples of the dioecious species C. (sect. Desvauxia) canescens Desvaux & LoiseleurDeslongchamps formed a robust monophyletic group, in which the rbcL gene sequence from C. altaica is identical to those from 4 parthenogenetic samples, but different from 6 other bisexual and parthenogenetic samples of C. canescens.