Data from: A total evidence approach to understanding phylogenetic relationships and ecological diversity in Selaginella subg. Tetragonostachys

Premise of the Study: Several members of Selaginella are renowned for their ability to survive extreme drought and “resurrect” when conditions improve. Many of these belong to subgenus Tetragonostachys, a group of ∼45 species primarily found in North and Central America, with substantial diversity in the Sonoran and Chihuahuan Deserts. We evaluated the monophyly and the age of subgenus Tetragonostachys and assess how drought tolerance contributed to the evolution of this clade. Methods: Our study included most Tetragonostachys species, using plastid and nuclear sequences, fossil and herbarium records, and climate variables to describe the species diversity, phylogenetic relationships, divergence times, and climatic niche evolution in the subgenus. Key Results: We found that subgenus Tetragonostachys forms a monophyletic group sister to Selaginella lepidophylla and may have diverged from other Selaginella because of a Gondwanan–Laurasian vicariance event ca. 240 mya. The North American radiation of Tetragonostachys appears to be much more recent and to have occurred during the Early Cretaceous–late Paleocene interval. We identified two significant and nested ecological niche shifts during the evolution of Tetragonostachys associated with extreme drought tolerance and a more recent shift to cold climates. Our analyses suggest that drought tolerance evolved in the warm deserts of southwest North America and may have been advantageous for colonization of cold and dry boreal climates. Conclusions: Our investigation provides a foundation for future research addressing the genomics of ecological niche evolution and the potential role of reticulate evolution in Selaginella subgenus Tetragonostachys.

研究背景：卷柏属（Selaginella）的多个类群以极端耐旱、环境改善后可“复苏”的特性而享誉学界，其中多数类群隶属于四穗卷柏亚属（Tetragonostachys）。该亚属约含45个物种，主要分布于北美与中美洲，在索诺兰沙漠及奇瓦瓦沙漠中物种多样性尤为突出。本研究旨在评估四穗卷柏亚属的单系性及其分化时间，并探究耐旱性对该演化支演化的贡献。
研究方法：本研究涵盖四穗卷柏亚属的绝大多数物种，通过质体序列与核序列、化石及标本馆记录、气候变量，对该亚属的物种多样性、系统发育关系、分化时间及气候生态位演化展开分析。
主要结果：研究发现，四穗卷柏亚属构成一单系群，为鳞叶卷柏（Selaginella lepidophylla）的姐妹群；该亚属可能因冈瓦纳-劳伦大陆隔离事件，于约2.4亿年前从其他卷柏类群中分化而来。四穗卷柏亚属的北美物种辐射演化时间则晚得多，发生于早白垩世至古新世晚期。本研究还鉴定出该亚属演化过程中两次显著且嵌套式的生态位转移事件：其一与极端耐旱性相关，其二则是更晚近的向寒冷气候的生态位转移。分析结果表明，耐旱性演化起源于北美西南部的暖沙漠环境，该特性或为该类群拓殖寒冷干燥的北方气候提供了适应性优势。
结论：本研究为后续探究卷柏属四穗卷柏亚属生态位演化的基因组学基础，以及网状演化在该亚属中的潜在作用奠定了研究框架。