Insights into cryptic speciation of quillworts in China.

Cryptic species are commonly misidentified because of high morphological similarities to other species. One group of plants that may harbor large numbers of cryptic species is the quillworts ( spp.), an ancient aquatic plant lineage. Although over 350 species of have been reported globally, only ten species have been recorded in China. The aim of this study is to better understand species diversity in China. For this purpose, we systematically explored the phylogeny and evolution of using complete chloroplast genome (plastome) data, spore morphology, chromosome number, genetic structure, and haplotypes of almost all Chinese populations. We identified three ploidy levels of in China-diploid (2 = 22), tetraploid (2 = 44), and hexaploid (2 = 66). We also found four megaspore and microspore ornamentation types in diploids, six in tetraploids, and three in hexaploids. Phylogenetic analyses confirmed that . as the ancestral group of the genus and revealed that diploids, tetraploids, and hexaploids do not form monophyletic clades. Most individual species possess a single genetic structure; however, several samples have conflicting positions on the phylogenetic tree based on SNPs and the tree based on plastome data. All 36 samples shared 22 haplotypes. Divergence time analysis showed that . diverged in the early Eocene (∼48.05 Ma), and most other species diverged 3-20 Ma. Additionally, different species of were found to inhabit different water systems and environments along the Yangtze River. These findings provide new insights into the relationships among species in China, where highly similar morphologic populations may harbor many cryptic species.