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

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. 概要 笔者在四川省措普湖附近发现了龙胆属高山组 (Genti- ana section Frigida) 的一种植物。虽然《Flora of China》将其 归为高山龙胆 (G. algida), 但其在形态特征上与西伯利亚和北美 洲的个体存在明显差异。本研究对其形态特征进行了调查,随 后基于叶绿体全基因组序列和完整ITS序列进行系统发育关系 分析,并比较了叶绿体基因组的结构变异。结果表明,措普湖的 高山龙胆种群与其他地区的样品不在同一遗传支系上,支持将 其作为一个新种——巴塘龙胆 (G. susanneae), 并在此对其进 行了描述