Phylogenetic relationships and diversification dynamics of Cerastium (Alsineae: Caryophyllaceae): implications for biogeographical patterns of herbs in the Northern Hemisphere

The evolutionary history of herbaceous species in the Northern Hemisphere remains poorly understood. The genus Cerastium is one of the most species-rich herbaceous genera in the Alsineae (Caryophyllaceae), and is mainly distributed in the Northern Hemisphere. Thus, it provides an ideal opportunity to explore the biogeographical history of herbs in the Northern Hemisphere. Here, we present a comprehensive phylogenetic tree for Cerastium with 75 species based on one nuclear and five plastid DNA markers. We then use an integrated phylogenetic, molecular dating, biogeographical, and diversification rate method to examine the spatiotemporal evolution of Cerastium. Cerastium is strongly supported as monophyletic and contains three major clades (Orthodon, Strephodon, and C. fragillimum). Cerastium originated from Europe in the middle Miocene (c. 13.45 million years ago), and subsequently colonized the New World, Africa, Asia, and Australasia through multiple intercontinental dispersal events. The dispersal of Cerastium from Europe (to both the East and West) and subsequent diversifications contributed to the formation of its contemporary Holarctic distribution pattern. The genus experienced rapid lineage accumulation during the late Miocene, possibly coinciding with a global decrease in temperature. These findings highlight the importance of the Northern Hemisphere in herbaceous species diversification in the late Miocene and Pliocene, and will deepen our understanding of the evolution of herbaceous plants.