Natural Hybrid Origin of the Controversial “Species” Clematis × pinnata (Ranunculaceae) Based on Multidisciplinary Evidence

• DOI: 10.3389/fpls.2021.745988
• Publication Date: 2021-10-13T17:32:22Z
• Authors: Rudan Lyu; Jian He; Yike Luo; Lele Lin; Min Yao; Jin Cheng; Lei Xie; Linying Pei; Shuangxi Yan; Liangqian Li
• Keywords: phylogenomic analysis; 0303 health sciences; 03 medical and health sciences; niche modeling; morphology; species status; Plant culture; Plant Science; 15. Life on land; homoploid hybridization; Clematis; SB1-1110

Interspecific hybridization is common and has often been viewed as a driving force of plant diversity. However, it raises taxonomic problems and thus impacts biodiversity estimation and biological conservation. Although previous molecular phylogenetic studies suggested that interspecific hybridization may be rather common inClematis, and artificial hybridization has been widely applied to produce newClematiscultivars for nearly two centuries, the issue of natural hybridization ofClematishas never been addressed in detail. In this study, we tested the hybrid origin of a mesophytic and cold-adapted vine species,Clematis pinnata, which is a rare and taxonomically controversial taxon endemic to northern China. Using field investigations, flow cytometry (FCM), phylogenomic analysis, morphological statistics, and niche modeling, we tested hybrid origin and species status ofC. pinnata. The FCM results showed that all the tested species were homoploid (2n = 16). Phylonet and HyDe analyses based on transcriptome data showed the hybrid origins ofC.×pinnatafrom eitherC. brevicaudata×C. heracleifoliaorC. brevicaudata×C. tubulosa. The plastome phylogeny depicted thatC.×pinnatain different sampling sites originated by different hybridization events. Morphological analysis showed intermediacy ofC.×pinnatabetween its putative parental species in many qualitative and quantitative characters. Niche modeling results suggested thatC.×pinnatahad not been adapted to a novel ecological niche independent of its putative parents. These findings demonstrated that plants ofC.×pinnatadid not formed a self-evolved clade and should not be treated as a species. The present study also suggests that interspecific hybridization is a common mechanism inClematisto generate diversity and variation, and it may play an important role in the evolution and diversification of this genus. Our study implies that morphological diversity caused by natural hybridization may overstate the real species diversity inClematis.