Molecular data of the Sphagnum cuspidatum complex relative to taxonomy

The use of species as a concept is an important metric for assessing biological diversity and ecosystem function. However, delimiting species based on morphological characters can be difficult, especially in aquatic plants that exhibit high levels of variation and overlap. The Sphagnum cuspidatum complex, which includes plants that dominate peatland hollows close to or at the water table, provides an example of challenges in species delimitation. Microscopic characters that have been used to define taxa and the possibility that these characters may simply be phenoplastic responses to variation in water availability make species delimitation in this group especially difficult. In particular, the use of leaf shape and serration, which have been used to separate species in the complex, have resulted in divergent taxonomic treatments. Using a combination of high-resolution population genomic data (RADseq) and a robust morphological assessment of plants representing the focal species, we provide evidence to evaluate putative species in this complex. Our results are broadly relevant to other aquatic groups where leaf shape and marginal teeth are used to distinguish species.

物种概念是评估生物多样性与生态系统功能的重要指标。然而，基于形态性状开展物种界定颇具难度，尤其是在变异程度高且性状重叠现象显著的水生植物类群中。尖叶泥炭藓（Sphagnum cuspidatum）复合群便是物种界定难题的典型案例：该复合群包含了广泛分布于接近或处于地下水位的泥炭地洼地中的优势植物。以往用于界定分类群的显微性状，以及这些性状可能仅仅是对水分可获得性变异的表型可塑性响应的可能性，使得该类群的物种界定工作尤为困难。尤为特殊的是，以往用于区分该复合群物种的叶形与叶缘锯齿性状，导致了不同的分类处理方案。本研究结合高分辨率群体基因组数据（RADseq）与对目标物种植株的严谨形态学评估，为评估该复合群内的推定物种提供了证据支持。本研究结果对其他以叶形和叶缘齿状特征区分物种的水生类群具有广泛的参考价值。