Multiple evidence shining a light on species delimitation in the tree genus Catalpa Scop.(Bignoniaceae)of China

Catalpa genus are distributed in South America,North America and East Asia.The existing taxonomy and phylogenetic studies of Catalpa focus on the evolution among intercontinental,and there are few studies on the field resources in China.In the latest taxonomic revision,the species of Catalpa in China were revised to Catalpa ovata and Catalpa bungei,and the rest were synonyms.However,the observation of greater morphological diversity than previously captured by the current taxonomic framework.Delimiting species requires multiple evidence,this research used integrative classification to explore species delimitation of Catalpa in China.On the basis of field investigation,Catalpa plants were pre-classified into six hypothetical species according to morphological and ecological species concepts.Subsequently,the DNA samples of six taxa were collected,the SNPs obtained by genotyping-by-sequencing(GBS)and chloroplast genome data were used to explore the species delimitation of Catalpa.The results showed that Chinese Catalpa contained at least three clade,and supported that C.fargesii was an independent species,not a synonym of C.bungei.In addition,there are two mystical taxa in the genus Catalpa in China,C.jinsiqiu and C.huangxin,which belong to different clade,and are not synonyms of existing species.The study found that there is a common gene introgression in Chinese Catalpa species,and the role of this phenomenon in the formation of species needs further research.This study provides a paradigm for the integrative taxonomy approach of plants and lays a foundation for the research and protection of Catalpa.