Tseng Yu-Hsin, Monro Alex K, Hu Jer-Ming
Department of Life Sciences, National Chung Hsing University, 145 Xingda Rd., South Dist., Taichung, 40227, Taiwan.
Herbarium, Royal Botanic Gardens, Kew, London, TW9 3AE, UK.
Bot Stud. 2025 Mar 19;66(1):10. doi: 10.1186/s40529-025-00456-0.
The paleotropics, home to half of Earth's rainforests, exhibit remarkable biodiversity and complex biogeographic patterns. Understanding the intercontinental distribution of plant taxa between Africa and Asia in this region is crucial for resolving longstanding debates on plant evolution and dispersal mechanisms. This study investigates the genus Elatostema, a widely distributed taxon found in subtropical and tropical Africa, Asia, and Australasia, aiming to elucidate the factors shaping its modern tropical disjunctions and evolutionary history.
Using molecular dating and ancestral area reconstruction, we reconstructed the historical biogeographic pattern of Elatostema. Our results indicated that the genus originated in tropical Asia during the Eocene, likely associated with boreotropical floras. The evolutionary history of Elatostema involved multiple intercontinental dispersal events, including two independent colonizations of Africa from Asia. Diversification within the core Elatostema clade was primarily driven by events in Asia and Oceania, with key factors contributing to this diversification including reciprocal dispersal between Malesia and Australasia, eastward island hopping and karstification in China. Furthermore, a geographical phylogenetic structure was observed within the core Elatostema clade, possibly due to limited seed and pollen dispersal.
The present study provides the first comprehensive insights into the biogeography and evolution of Elatostema. The presence of numerous narrowly distributed endemics, relatively few widespread species, and geographical structures within Elatostema suggest that limited gene flow may be a crucial factor in speciation and evolutionary processes, similar to other species-rich genera.
古热带地区拥有地球上一半的雨林，展现出显著的生物多样性和复杂的生物地理格局。了解该地区非洲和亚洲之间植物类群的洲际分布，对于解决有关植物进化和扩散机制的长期争论至关重要。本研究调查了楼梯草属，这是一个广泛分布于亚热带和热带非洲、亚洲及澳大拉西亚的类群，旨在阐明塑造其现代热带间断分布和进化历史的因素。
利用分子定年和祖先分布区重建，我们重建了楼梯草属的历史生物地理格局。我们的结果表明，该属在始新世起源于热带亚洲，可能与北热带植物区系有关。楼梯草属的进化历史涉及多次洲际扩散事件，包括两次从亚洲到非洲的独立定殖。核心楼梯草属分支内的多样化主要由亚洲和大洋洲的事件驱动，促成这种多样化的关键因素包括马来群岛和澳大拉西亚之间的相互扩散、中国的东向跳岛和岩溶作用。此外，在核心楼梯草属分支内观察到地理系统发育结构，这可能是由于种子和花粉扩散有限所致。
本研究首次对楼梯草属的生物地理学和进化提供了全面的见解。楼梯草属中存在众多分布狭窄的特有种、相对较少的广布种以及地理结构，这表明有限的基因流可能是物种形成和进化过程中的关键因素，这与其他物种丰富的属类似。
