Chloroplast phylogeography of Iris dichotoma (Iridaceae), a widespread herbaceous species in East Asia

Both a complex topography and climate change have huge impacts on the distribution and genetic structure of extant species. Due to the lack of relevant molecular research, little is definitively known about the phylogeography of herbaceous plants in East Asia. Here we investigate the genetic diversity, population structure and historical population dynamics of Iris dichotoma Pallas, a widespread perennial herbaceous species in northeastern and northern China. Twenty-nine populations, totalling 297 individuals, were sampled throughout the Chinese distributional range of I. dichotoma. The combined sequences of six chloroplast DNA fragments (petA-psbE, rps18-clpp, psbJ-petA, trnD-trnT, rps16 and ndhA) were used to identify 13 haplotypes, of which six were private ones restricted in a single population. Genetic differentiation among I. dichotoma populations, enabled us to infer potential refugia during the glacial period in the Yinshan Mountains-Yanshan Mountains, where high levels of haplotype and nucleotide diversity were detected. The results of a neutral test and mismatch distribution analysis both indicated that I. dichotoma underwent a recent population expansion. In East Asia, postglacial environmental and climatic changes appear to have promoted genetic diversification not only in better-studied woody species, but also in herbaceous ones like I. dichotoma. Future studies of more herbaceous plant species are needed to obtain better insight into how modern temperate biodiversity has developed in East Asia.