Molecular phylogeny and the biogeographic origin of east asian isoёtes (Isoёtaceae)

Abstract

Isoёtes L. (Isoёtaceae) is a cosmopolitan genus of heterosporous lycopods containing ca. 200 spe- cies being found in lakes, streams, and wetlands of terrestrial habitats. Despite its ancient origin, worldwide dis- tribution, and adaptation to diverse environment, species in Isoёtes show remarkable morphological simplicity and convergence. Allopolyploidy appears to be a significant speciation process in the genus. These character- istics have made it difficult to assess the phylogenetic relationships and biogeographic history of Isoёtes spe- cies. In recent years, these difficulties have somewhat been reduced by employing multiple molecular markers. Here, we reconstruct the phylogenetic relationships in East Asian Isoёtes species. We also provide their diver- gence time and biogeographic origin using a fossil calibrated chronogram. East Asian Isoёtes species are divided into two clades: I. asiatica and the remaining species. Isoёtes asiatica from Hokkaido forms a clade with north- eastern Russian and western North American Isoёtes species. In clade I, western North America is the source area for the dispersal of Isoёtes to Hokkaido and northeastern Russia via the Bering land bridge during the late Miocene. The remaining Isoёtes species (I. sinensis, I. yunguiensis, I. hypsophila, I. orientalis, I. japonica, I. coreana, I. taiwanensis, I. jejuensis, I. hallasanensis) from East Asia form a sister group to Papua New Guinean and Australian species. The biogeographic reconstruction suggests an Australian origin for the East Asian spe- cies that arose through long-distance dispersal during the late Oligocene.