The Himalaya–Hengduan Mountain (HHM) region consists of two global biodiversity hotspots characterized by a high degree of plant endemism. However, little is known about how these endemic species are formed and maintained in relation to the regional geomorphology of the past or current time. Thus, this study investigated the genetic structure of the herbaceous genus Acanthocalyx (Caprifoliaceae) endemic to the HHM to demonstrate if major geographic or ecological barriers in the HHM region have influenced its phylogeographic patterns. Our analyses revealed distinct genetic structures within A. alba and A. nepalensis and indicated that A. delavayi may have recently evolved from isolated peripheral populations of A. nepalensis. In particular, we not only confirmed a well-known genetic structure of alpine plants between the Himalayas and the Hengduan Mountains but also discovered a notable floristic boundary (bounded by 30° to 31°N latitude) within the Hengduan Mountains from A. alba. This study provides new insights into the dispersal and intraspecific genetic variation of Acanthocalyx and highlights the importance of geomorphological features for the diversification of HHM alpine flora.

喜马拉雅-横断山 (HHM) 地区由两个全球生物多样性热点组成，其特征是高度的植物特有。然而，关于这些地方性物种是如何形成和维持与过去或现在的区域地貌相关的知之甚少。因此，本研究调查了HHM 特有的草本属Acanthocalyx (Caprifoliaceae)的遗传结构，以证明 HHM 地区的主要地理或生态障碍是否影响了其系统地理学模式。我们的分析揭示了A. alba和A. nepalensis内不同的遗传结构，并表明A. delavayi最近可能是从孤立的外围种群进化而来的A.冬瓜。特别是，我们不仅证实喜马拉雅和横断山之间高山植物的一个公知的遗传结构，但也发现了横断山脉内从一个显着的植物区系边界（由30°至31°N纬度为界）A.杨。这项研究为Acanthocalyx的分散和种内遗传变异提供了新的见解，并强调了地貌特征对 HHM 高山植物群多样化的重要性。