Recent diversification of Aneuraceae, an ancient family of simple thalloid liverworts

Aneuraceae, the largest family of simple thalloid liverworts, is recognised for its unique ecology and cryptic diversity despite its simple morphological features. In the present study, we explored the evolutionary history and diversification of Aneuraceae, focusing on the effects of fossil calibrations on divergence time estimates and the significance of including cryptic species in macroevolutionary analyses. We used publicly available nucleotide sequences to reconstruct chronograms of Aneuraceae, incorporating other representatives from subclass Metzgeriidae as outgroups. We also assessed the effects of various calibration approaches on chronogram reconstruction. The resulting time-calibrated phylogeny was subjected to time plots, γ-statistics, and Bayesian analysis of macroevolutionary mixtures (BAMM) to uncover diversification dynamics within the Aneuraceae lineage. Aneuraceae originated and diversified from the Upper Devonian (358.04 Mya, 95% highest posterior density: 513.61–268.36) to the Lower Carboniferous period. Our analysis revealed late bursts of diversification, with significant rate shifts at the crown node of the genus <i>Riccardia</i> and at the Neotropical clade within <i>Riccardia</i>. Including cryptic taxa in the analyses introduced an additional rate shift at the crown node of the genus <i>Aneura</i>. Aneuraceae probably originated during the middle Paleozoic, like other early terrestrial plants, although different fossil-calibration approaches significantly influenced the divergence time estimates. The speciation rate shifts in <i>Riccardia</i> could be attributed to asexual reproduction within this genus, as well as climate changes and geological events in the Neotropics. Ecological conditions at the origin of Aneuraceae may have played a role in driving its increased diversification.

被叶苔科（Aneuraceae）是简单叶状体苔类（thalloid liverworts）中最大的一科，尽管其形态结构简洁，却以独特的生态特征与隐蔽的物种多样性而广受认可。本研究探讨了被叶苔科的演化历史与物种分化历程，重点聚焦于化石校准对分化时间估算的影响，以及纳入隐蔽物种在宏观演化分析（macroevolutionary analyses）中的重要意义。研究采用公开可用的核苷酸序列（nucleotide sequences），重建了被叶苔科的时间树（chronograms），同时以叉苔亚纲（Metzgeriidae）的其他代表类群作为外类群（outgroups）。此外，本研究还评估了多种校准方法对时间树重建的影响。基于得到的时间校准系统发育树，我们通过时间序列分析、γ统计量（γ-statistics）以及宏观演化混合贝叶斯分析（Bayesian Analysis of Macroevolutionary Mixtures, BAMM），探究了被叶苔科支系内的物种分化动态。被叶苔科的起源与物种分化时间跨度为晚泥盆世（358.04百万年前，95%最高后验密度（highest posterior density）区间：513.61–268.36）至早石炭世。分析结果显示该科存在晚期的物种分化爆发，在瑞氏苔属（Riccardia）的冠节点（crown node）以及瑞氏苔属内的新热带支系（clade）处均发生了显著的演化速率转变。若在分析中纳入隐蔽类群，则会在被蒴苔属（Aneura）的冠节点处新增一处演化速率转变事件。与其他早期陆生植物类似，被叶苔科大概率起源于中古生代，但不同的化石校准方法会对分化时间估算结果产生显著影响。瑞氏苔属的物种形成速率转变可能与该属的无性繁殖（asexual reproduction）、新热带区的气候变化及地质事件相关。被叶苔科起源时的生态环境条件可能是推动其物种多样性提升的重要因素。