关键词: 多肉植物, 龙树科, 分化时间, 系统发育, 物种分化

Abstract: Aims Climate change has significantly influenced the evolutionary history of various biological groups. Among these, the succulents are special plant groups adapted to arid climate conditions. Didiereaceae, a small family circumscribed within Caryophyllales, consist of about 20 species representing 6 genera and 3 subfamilies. Species of the family are succulent plants and are distributed in the arid regions of the southern to eastern African continent and Madagascar. However, the link between the family’s evolution and the establishment of drought climates in its habitats remains unclear. Methods In this study, the phylogenetic relationships among Didiereaceae speceis were reconstructed based on analyses of six plastid DNA markers (viz. rps16, rpl16, trnL-F, trnT-trnL, trnG-S, trnQ-rps16). Additionally, molecular dating and diversification analyses of the family were conducted. Important findings The monophyly of Didiereaceae was strongly supported, and a robust phylogenetic framework for the family was established. The crown age of the family was estimated to be approximately 62.3 million years ago (Ma) in the middle Paleocene. However, the two subfamilies (viz. Didiereoideae and Portulacarioideae) with multiple species began to diverge around 11.1 Ma and 14.9 Ma, respectively, during the mid-late Miocene. Result from diversification analysis further revealed that an increased diversification rate shift in the family may have occurred around 11 Ma. These findings align closely with the timing of the establishment of arid climates (15–10 Ma) in the regions where the family is distributed. Therefore, we suggest that the establishment of arid conditions in southern to eastern Africa and Madagascar during the mid-late Miocene likely played a significant role in driving species diversification within the succulent family Didiereaceae. This study not only enhances our understanding of the evolutionary history of Didiereaceae, but also contributes to the broader knowledge of species diversification patterns in succulent plants.

Key words: Didiereaceae, Divergence time, Phylogeny, Succulent plants, Species diversification