2025 Volume 100 Issue 1 Pages 3-17
Plants of Podostemaceae inhabit only rock surfaces submerged in swift currents. Recent research showed the great diversity with many new taxa and gave molecular and phenetic evidence of their evolutionary history. Drastic ecological change may have preceded the diversification in the relatively little-varied environments. Each subfamily originated in either Asia or America and two subfamilies extended to the other continent, resulting in double-layer biogeography. The biogeography in Japan and elsewhere is affected by volcanic activities. There are great genetic differences between geographic populations, which can produce paraphyletic species. A species was cultured, with an implication that in nature currents sweep away harmful microorganisms and supply nutrition. The mutation rate of the family, which was found to be much higher than that of allied families, is probably caused primarily by exposure to intense ultraviolet irradiation. Genetically, the typical-meristemless stem is integrated with the Podostemoideae ‘leaf’ and ‘bract’. The evolution of rootedness/ rootlessness, organographic composition, and so on is saltational. The evolutionary change of foliose to ribbon-like roots, whose difference little affects adhesion to rocks, may be neutral.
