Abstract:

Didymodon Hedw., with approximately 140 species in the family Pottiaceae, is distributed nearly throughout the world, with the greatest diversity and important ecological functions in drought lands and alpine ecosystems. Several studies involving morphology, molecular systematics, and macro-systematic analysis have addressed the infrageneric classification of Didymodon, but controversy over the position of the infrageneric and species classification remains due to its high degree of morphological variation in micro-habitats and strong sensitivity to climate change at regional and global scale. To date, only a few phylogenetic studies have been conducted with an incomplete number of Didymodon species; further, there is no study published regarding the divergence time of Didymodon. Consequently, we conducted a comprehensive phylogenetic analysis of Didymodon species, sampling a total of 107 species, based on one nuclear (ITS) and five chloroplast DNA. Moreover, divergence time analysis was conducted to infer the age of origin and divergence of Didymodon species. Our results presented the largest scale phylogenetic relationship of Didymodon to date and resolved the phylogenetic status of some controversial taxa and the new species. The divergence time estimation showed that Didymodon species originated around the early Cretaceous, and the diversification was concentrated in the Cretaceous and Eocene. Paleoclimate and environmental change have a direct impact on the origin and divergence of Didymodon species by shaping their morphology, resource availability and ecological niche. Our study will help understand species origin and speciation of Didymodon as well as reflecting species adaptability and experience to historical events.

Key words: Didymodon, diversification, molecular phylogenetics, taxonomy