Phylogeny And Biogeography Of The Impatiens Sect.Racemosae(Balsaminaceae)

Impatiens sect.Racemosae S.X.Yu & Wei Wang belongs to Balsaminaceae of Impatiens L.,which was established by Yu Shengxiang et al.in 2016 based on morphological traits and molecular evidence.There are about 70 species in sect.Racemosae,which are concentrated in southwestern China and the Himalayas,showing a Chinese-Himalayan distribution pattern.A few species are distributed to Central Asia and Europe.Previous studies mainly explored the phylogenetic relationship of this sect.Racemosae based on limited sampling and a few molecular fragments.The phylogeny and biogeography of the sect.Racemosae are still unclear.Therefore,the phylogenetic relationship,spatial and temporal evolution pattern and modern distribution pattern of the sect.Racemosae need to be further explored.In this study,55 species(56 samples),accounting for about 79 % of sect.Racemosae,were selected based on a wide range of worldwide sampling of plants in sect.Racemosae.The chloroplast genome and 80 protein-coding gene tandem sequences were used for the first time.The two matrices are based on two tree-building methods,namely,Maximum Likelihood tree(ML)and Bayesian tree(BI),to perform phylogenetic analysis of sect.Racemosae.Based on the stable phylogenetic tree constructed in this study,the biogeography research integrates the methods of divergence time estimation,reconstruction of ancestral distribution area,divergence rate,principal component analysis and Qua SSE model analysis to study the origin,migration and diversification of this sect.Racemosae of plants.Events,and in-depth discussion of the spatial and temporal evolution pattern and current distribution pattern of sect.Racemosae.The main results of this paper are as follows:(1)In molecular systematics,based on the chloroplast genome data,the phylogenetic relationship of sect.Racemosae was reconstructed by different analysis methods for the first time.The results support that sect.Racemosae is a monophyletic group with strong support,and sect.Racemosae is redivided into five major branches.First,the base group Clade I and the remaining species form a sister group with high support(PP = 1.00,BS = 100 %),and then Clade II and Clade III-Clade IV-Clade V form a sister group with high support(PP = 1.00,BS = 100 %).Subsequently,Clade III and Clade IV-Clade V formed a sister group with high support(PP = 1.00,BS = 100 %).Finally,Clade IV and Clade V formed a sister group with high support(PP = 1.00,BS= 100 %).The results are supported by high molecular evidence.(2)Analysis of differentiation time and biogeography shows that the most recent common ancestor of sect.Racemosae may have originated in the Himalayas in the middle Miocene(14.71Ma),which may be related to the uplift of the Qinghai-Tibet Plateau(16-14Ma)and the Himalayas-Hengduan Mountains orogenic movement(15Ma).In the late Pliocene(3.56Ma),it successfully spread to the Hengduan Mountains-South China region,and in the late Pliocene(2.86Ma),it first spread to Central Asia-Europe,which may be related to the global climate cooling.These geological events and climate changes have created highly isolated and diverse habitats and promoted the origin and differentiation of sect.Racemosae plants.(3)In the study of species diversity of sect.Racemosae,Hengduan Mountain area is the area with the highest species richness of sect.Racemosae(48.15 %),followed by Himalayan Mountain area(46.29 %).Seasonal rainfall is an important factor affecting the distribution of sect.Racemosae plants,especially Clade V branch,followed by thermal change.Due to the unique topography of the Hengduan Mountains,the continuous flow of hot and humid air has greatly promoted the formation of sect.Racemosae species.The second is the long-term monsoonal seasonal rainfall south of the Himalayas.In addition,the results of niche breadth-diversity relationship showed that narrower niches were more helpful for species to cope with climate fluctuations,occupy microhabitats and promote differentiation at high altitudes.This study constructed a phylogenetic tree with the most complete sampling of the sect.Racemosae so far,supporting the monophyly of sect.Racemosae,and divided five main branches with support rates under sect.Racemosae.Based on this phylogenetic relationship,the biogeography of this sect.Racemosae plants and the causes of the distribution pattern of existing species are discussed.The research results are helpful to understand the evolutionary history and causes of this sect.Racemosae,and also provide an important reference for revealing the biogeography of the ChineseHimalayan flora.