Rediscovery of Craspedosorus and Plastome-Based Evidence for Its Synonymy With Leptogramma (Thelypteridaceae)

Yunnan Province is the richest region in China for lycophytes and ferns. Its unique geological history and climatic conditions have nurtured numerous endemic and rare plant species. Craspedosorus, a monotypic genus of Thelypteridaceae containing only Craspedosorus sinensis, is a genus endemic to Yunnan, China. It was first discovered and described in the 1970s. However, since its initial discovery in 1973, there have been no subsequent field observations or collection records. Moreover, due to a lack of molecular data, Craspedosorus remains the only fern genus in China without such data and has long had a controversial systematic position. This study rediscovered a population of only 15 mature individuals in Yongshan County, Zhaotong City, Yunnan Province, 52 years after its initial discovery. Using flow cytometry, it was confirmed that Craspedosorus sinensis is diploid, with a genome size of approximately 5.12 Gb. Molecular phylogenetic analyses further determined that C. sinensis belongs to Section Haplogramma (K. Iwatsuki) L.Y. Kuo & Y.H. Chang of the genus Leptogramma, and Craspedosorus therefore should be treated as a synonym of Leptogramma. This research is significant for understanding the taxonomy, distribution, and phylogeny of Leptogramma.