A phylogenomic‐based new taxonomy and biogeographic history of the genus Piptanthus (Leguminosae)

Abstract The Qinghai‐Tibet Plateau and the Hengduan Mountains, which are among the world's key biodiversity hotspots, have long captivated botanists. Piptanthus , a genus of evergreen shrubs in the tribe Thermopsideae (Leguminosae, Papilionoideae), is an endemic and distinctive element of this region. Historically, the genus was considered to comprise two or three species, but species delimitation has been contentious due to a lack of comprehensive research on its morphological variation, distribution patterns, and evolutionary history. In this study, we map a more detailed distribution range of the genus, infer its historical biogeography, and propose species delimitation by integrating newly collected chloroplast genome and morphological data. Our findings indicate that Piptanthus should be treated as a single species, viz. Piptanthus nepalensis , which is broadly distributed from the Himalayas to the Hengduan‐Arakan Mountains. We estimate that the genus diverged with Anagyris at c. 6.8 Ma, subsequently splitting into two clades at c. 5.67 Ma: one in the Qinling Mountains and the other in the Himalaya‐Hengduan‐Arakan Mountains. The Hengduan‐Arakan (Myanmar) clade is relatively young, with an estimated crown group time at c. 2.39 Ma, likely resulting from adaptation to newly formed forest habitats following the southward migration of forests after the secondary uplift of the Qinghai‐Tibet Plateau.