Phylogenetics Support the Description of a New Sichuanese Species, Susanne’s Gentian, Gentiana susanneae (Gentianaceae)

Abstract

Abstract— The region of the Qinghai-Tibet Plateau hosts a remarkable biodiversity, including a plethora of endemics. There, the process of documenting biodiversity is still ongoing, and recently, an unusual plant of Gentiana section Frigida was discovered at Cuopu Lakes (Sichuan, China). Although Flora of China identified these specimens as G. algida based upon unmistakable traits (e.g. corolla colour and length, sessile flowers), it was obvious that the Sichuanese plants strongly differed morphologically from G. algida specimens from Siberia and North America. In order to clarify their relationships, we used an integrative approach, investigating not only morphological traits, but also phylogenetic relationships (based upon plastome and rDNA-cistron), as well as chloroplast structure. Whereas the rDNA-cistron phylogeny was poorly resolved, the plastome phylogeny was well supported in both Bayesian inference and maximum likelihood analyses. Our findings indicate that the samples of G. algida from Cuopu Lakes are morphologically and genetically distinct from those collected elsewhere, supporting the recognition of a new species, G. susanneae. The new species differs from G. purdomii (another similar species) by having sessile flowers, and from G. algida by being a generally much taller plant with more and longer flowers, and by having a smaller calyx. Gentiana susanneae clusters with other species from the region of the Qinghai-Tibet Plateau from which it differs morphologically, and is only distantly related to the G. algida/G. frigida clade, which stems from a dispersal event out of Tibet. Based upon these solid lines of evidence, G. susanneae is described and illustrated (drawings and photographs). In addition, a conservation assessment and an identification key modified from Flora of China are provided.