Premise: Glacial/interglacial cycles and topographic complexity are both considered to have shaped today's diverse phylogeographic patterns of taxa from unglaciated eastern North America (ENA). However, few studies have focused on the phylogeography and population dynamics of wide-ranging ENA herbaceous species occurring in forest understory habitat. We examined the phylogeographic pattern and evolutionary history of Podophyllum peltatum L., a widely distributed herb inhabiting deciduous forests of ENA.
Methods: Using chloroplast DNA (cpDNA) sequences and nuclear microsatellite loci, we investigated the population structure and genetic diversity of the species. Molecular dating, demographic history analyses, and ecological niche modeling were also performed to illustrate the phylogeographic patterns.
Results: Our cpDNA results identified three main groups that are largely congruent with boundaries along the Appalachian Mountains and the Mississippi River, two major geographic barriers in ENA. Populations located to the east of the Appalachians and along the central Appalachians exhibited relatively higher levels of genetic diversity. Extant lineages may have diverged during the late Miocene, and range expansions of different groups may have happened during the Pleistocene glacial/interglacial cycles.
Conclusions: Our findings indicate that geographic barriers may have started to facilitate the population divergence in P. peltatum before the Pleistocene. Persistence in multiple refugia, including areas around the central Appalachians during the Quaternary glacial period, and subsequent expansions under hospitable climatic condition, especially westward expansion, are likely responsible for the species' contemporary genetic structure and phylogeographic pattern.
冰期/间冰期循环和地形的复杂性都被认为是塑造当今北美东部类群多样的谱系地理式样的重要因素。然而，以北美东部广布草本植物的谱系地理与群体动态为焦点的研究还十分有限。本文关注北美东部一种广布的林下草本植物--足叶草（Podophyllum peltatum L.）的谱系地理式样与进化历史，使用叶绿体DNA序列和核微卫星位点探究了其群体结构与遗传多样性，并进行了分子定年、群体动态历史分析及生态位重建，以阐明其谱系地理式样。基于叶绿体DNA的分析将该物种划分为以北美东部两大地理屏障--阿巴拉契亚山脉和密西西比河为界的三个组。阿巴拉契亚山脉以东的群体和山脉中部的群体展现出了较高的遗传多样性。现存谱系可能于晚中新世产生了分化，而不同组分布范围的扩张可能发生于更新世的冰期/间冰期循环中。本研究揭示了地理屏障或在更新世之前就开始促进足叶草的群体分化；该物种在第四纪冰期可能居留于包括阿巴拉契亚山脉中部在内的多个避难所，并在气候变暖后发生了扩张，尤其是向西的扩张，最终导致了其当代遗传结构和谱系地理式样的产生。.
Keywords: Berberidaceae; Podophyllum peltatum; clonal diversity; demographic history; eastern North America; genetic diversity; genetic structure; phylogeographic inference; understory herb.
© 2023 Botanical Society of America.