Studies on extinction mechanisms and ex-situ preservation of Charales in lakes

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The current status of the Charales in Japan was investigated based on field surveys of 40 lakes from 1997 to 1999 and compared with that of the same lakes reported by Kasaki (1964). No charalean species have been found in 28 lakes during the last 33 years. Such extinction seems to be caused by eutrophication of lakes, the artificial introduction of grass carps or the artificial fluctuation of water level for hydroelectricity. Although 31 charalean taxa have been recorded from these lakes by Kasaki (1964), now only 6 taxa, Chara braunii, C. globularis var. globularis, C. corallina, Nitella flexilis var. flexilis, and N. hyalina, were found. Even these six taxa have disappeared in more than 50% of lakes surveyed. So it was judged that these taxa were in endangered state. The five taxa of Charales, Chara globularis var. hakonensis, C. fibrosa var. brevibracteata, Nitella flexilis var. bifurcata, N. furcata var. fallosa, N. minispora, are extinct from the world charalean flora, because all of them are endemic to Japanese lakes. Nitellopsis obtusa was extinct from the Japanese lakes, but the plant originated from Lake Nojiri, Nagano Prefecture, Japan were this species once grew is now cultured in the Microbial Culture Collection, National Institute for Environmental Studies. The other 20 taxa of Charales were extinct from the lakes. Since it is not clear whether these taxa still exist in the other wetland areas, it was considered that these taxa were in endangered state. The four endangered species, Chara braunii, C. globularis var. globularis, Nitella flexilis var. flexilis and Nitella gracilens and the wild-extinct species, Nitellopsis obtusa were successfully cultured and the oospore of N. gracilens were observed.