Solfatara fields, areas surrounding fumaroles near the hot springs or volcanoes, are characterized by severe environmental conditions such as low soil pH and high aluminum contents. Fimbristylis dichotoma subsp. podocarpa is an endangered plant distributed in solfatara fields of Kyushu, western Japan. They are considered as a conspecific of F. dichotoma var. tentsuki: which widely distributed in wetlands throughout the Japanese archipelago. However, in spite of the distinct difference in their habitats, little is known about their eco-physiological characteristics, and their phylogenetic relationships still remain to be clarified.
Thus, we conducted the culture experiments to compare the tolerance to low pH and aluminum concentration of them. As the result of the experiments, seedling growth of F. dichotoma var. tentsuki was suppressed at the low pH and aluminum concentrations. Conversely, no significant decline in the seedling growth was observed in F. dichotoma subsp. podocarpa at the same levels. In addition, we used the data of nuclear ribosomal internal transcribed spacer (ITS) in order to reconsider the taxonomic status of them. Consequently, the analysis reveals that F. dichotoma subsp. podocarpa is phylogenetically distant from F. dichotoma var. tentsuki. In conclusion, these results suggest that both species can be regarded as distinct species.