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Abstract PremiseSphagnum magellanicum(Sphagnaceae, Bryophyta) has been considered to be a single semi‐cosmopolitan species, but recent molecular analyses have shown that it comprises a complex of at least seven reciprocally monophyletic groups, that are difficult or impossible to distinguish morphologically. MethodsNewly developed barcode markers and RADseq analyses were used to identify species among 808 samples from 119 sites. Molecular approaches were used to assess the geographic ranges of four North American species, the frequency at which they occur sympatrically, and ecological differentiation among them. Microhabitats were classified with regard to hydrology and shade. Hierarchical modelling of species communities was used to assess climate variation among the species. Climate niches were projected back to 22,000 years BP to assess the likelihood that the North American species had sympatric ranges during the late Pleistocene. ResultsThe species exhibited parallel morphological variation, making them extremely difficult to distinguish phenotypically. Two to three species frequently co‐occurred within peatlands. They had broadly overlapping microhabitat and climate niches. Barcode‐ versus RADseq‐based identifications were in conflict for 6% of the samples and always involvedS. diabolicumvs.S. magniae. ConclusionsThese species co‐occur within peatlands at scales that could permit interbreeding, yet they remain largely distinct genetically and phylogenetically. The four cryptic species exhibited distinct geographic and ecological patterns. Conflicting identifications from barcode vs. RADseq analyses forS. diabolicumversusS. magniaecould reflect incomplete speciation or hybridization. They comprise a valuable study system for additional work on climate adaptation. 

Abstract 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, 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 data support the recognition of S. cuspidatum, S. fitzgeraldii, S. mississippiense, and S. trinitense as genetically distinct species that can be separated morphologically. These results indicate that S. viride does not differ genetically from S. cuspidatum. Our results are broadly relevant to other aquatic groups where leaf shape and marginal teeth are used to distinguish species. 

Abstract Climate change is affecting how energy and matter flow through ecosystems, thereby altering global carbon and nutrient cycles. Microorganisms play a fundamental role in carbon and nutrient cycling and are thus an integral link between ecosystems and climate. Here, we highlight a major black box hindering our ability to anticipate ecosystem climate responses: viral infections within complex microbial food webs. We show how understanding and predicting ecosystem responses to warming could be challenging—if not impossible—without accounting for the direct and indirect effects of viral infections on different microbes (bacteria, archaea, fungi, protists) that together perform diverse ecosystem functions. Importantly, understanding how rising temperatures associated with climate change influence viruses and virus-host dynamics is crucial to this task, yet is severely understudied. In this perspective, we (i) synthesize existing knowledge about virus-microbe-temperature interactions and (ii) identify important gaps to guide future investigations regarding how climate change might alter microbial food web effects on ecosystem functioning. To provide real-world context, we consider how these processes may operate in peatlands—globally significant carbon sinks that are threatened by climate change. We stress that understanding how warming affects biogeochemical cycles in any ecosystem hinges on disentangling complex interactions and temperature responses within microbial food webs. 

Abstract Peatlands are crucial sinks for atmospheric carbon but are critically threatened due to warming climates.Sphagnum(peat moss) species are keystone members of peatland communities where they actively engineer hyperacidic conditions, which improves their competitive advantage and accelerates ecosystem-level carbon sequestration. To dissect the molecular and physiological sources of this unique biology, we generated chromosome-scale genomes of twoSphagnumspecies:S. divinumandS. angustifolium.Sphagnumgenomes show no gene colinearity with any other reference genome to date, demonstrating thatSphagnumrepresents an unsampled lineage of land plant evolution. The genomes also revealed an average recombination rate an order of magnitude higher than vascular land plants and short putative U/V sex chromosomes. These newly described sex chromosomes interact with autosomal loci that significantly impact growth across diverse pH conditions. This discovery demonstrates that the ability ofSphagnumto sequester carbon in acidic peat bogs is mediated by interactions between sex, autosomes and environment. 

PremiseTheSphagnum recurvumcomplex comprises a group of closely related peat mosses that are dominant components of many northern wetland ecosystems. Taxonomic hypotheses for the group range from interpreting the whole complex as one polymorphic species to distinguishing 6–10 species. The complex occurs throughout the Northern Hemisphere, and some of the putative species have intercontinental ranges. Our goals were to delimit the complex and assess its phylogenetic structure in relation to morphologically defined species and intercontinental geography. MethodsRADseq analyses were applied to a sample of 384 collections from Europe, North America, and Asia. The data were subjected to maximum likelihood phylogenetic analyses and analyses of genetic structure using the software STRUCTURE and multivariate ordination approaches. ResultsTheS. recurvumcomplex includesS. angustifolium,S. fallax,S. flexuosum,S. pacificum, andS. recurvumas clades with little evidence of admixture. We also resolved an unnamed clade that is referred to here asS. “pseudopacificum.” We confirm thatS. balticumandS. obtusumare nested within the complex. Species with bluntly acute to obtuse stem leaf apices are sister to those with acute to apiculate leaves. Most of the species exhibit some differentiation between intraspecific population systems disjunct on different continents. ConclusionsWe recognize seven species in the amendedS. recurvumcomplex, includingS. balticumandS. obtusum, in addition to the informal cladeS. “pseudopacificum.” Although we detected some geographically correlated phylogenetic structure within widespread morphospecies, our RADseq data support the interpretation that these species have intercontinental geographic ranges. 

Species delimitation is problematic in many plant groups and among the mosses, Sphagnum is one of the more contentious genera because of high levels of morphological variation. The allopolyploid species, Sphagnum majus, comprises one such problematic complex. Two morphologically differentiated but overlapping subspecies have been described. We conducted morphometric and molecular analyses with samples from around the Northern Hemisphere to test for phenotypic and phylogenetic differentiation between the subspecies. Although field collections of the two species can be statistically differentiated morphologically, there is substantial overlap. Genome-scale molecular data do not suggest any differentiation between S. majus ssp. majus and ssp. norvegicum, including samples assigned to the two taxa from sympatric sites. Sequence data from the plastid genome were employed to infer parentage of allopolyploid S. majus. Our results support the hypothesis that S. annulatum is the paternal parent and S. cuspidatum is the maternal parent. We conclude that the morphological differences between them are either plastic responses to habitat heterogeneity or segregating genetic variation within a single taxon. Formal taxonomic recognition of two taxa is not supported by our molecular data.