BACKGROUND AND AIMS:Sphagnum imbricatum sensu lato (Sphagnum, subgenus Sphagnum) is sometimes considered a single widespread and polymorphic species, or up to four separate species. This study was conducted to provide a phylogenetic delimitation of the S. imbricatum complex, assess species delimitation within the complex, and evaluate likely parentage of five allopolyploid species in subgenus Sphagnum that may be related to haploid species in the complex. METHODS:RADSeq data were assembled from 192 samples of subgenus Sphagnum plus three outgroup taxa from related Sphagnum subgenera. Parentage of allopolyploids was assessed using STRUCTURE and differentially fixed SNPs among haploid taxa and their distribution within and among the allopolyploids. KEY RESULTS:The S. imbricatum complex was circumscribed to include S. affine, S. austinii, S. imbricatum, S. portoricense and S. steerei. The traditionally recognized species, S. affine, was resolved to include two morphologically similar clades that are phylogenetically divergent (non-sister groups) within the complex. All the northern allopolyploids were derived from crosses between species in the S. imbricatum and S. magellanicum complexes. CONCLUSIONS:The two clades formerly known as S. affine s.l. will need to be recognized as separate species pending in-progress morphological study. Our results suggest testable hypotheses about specific haploid taxa identified as likely parents of the allopolyploid species. Newly resolved phylogenetic relationships among species in the S. imbricatum complex indicate that the tropical species S. portoricense is nested within a clade otherwise distributed in arctic to temperate regions, empowering this group for research about warm climate adaptation utilizing naturally occurring variation.

ABSTRACT Sphagnum moss is the dominant plant genus in northern peatlands responsible for long‐term carbon accumulation. Sphagnum hosts diverse microbial communities (microbiomes), and its phytobiome (plant host + constituent microbiome + environment) plays a key role in nutrient acquisition along with carbon cycling. Climate change can modify the Sphagnum ‐associated microbiome, resulting in enhanced host growth and thermal acclimation as previously shown in warming experiments. However, the extent of microbiome benefits to the host and the influence of host–microbe specificity on Sphagnum thermal acclimation remain unclear. Here, we extracted Sphagnum microbiomes from five donor species of four peatland warming experiments across a latitudinal gradient and applied those microbiomes to three germ‐free Sphagnum species grown across a range of temperatures in the laboratory. Using this experimental system, we test if Sphagnum 's growth response to warming depends on the donor and/or recipient host species, and we determine how the microbiome's growth conditions in the field affect Sphagnum host growth across a range of temperatures in the laboratory. After 4 weeks, we found that the highest growth rate of recipient Sphagnum was observed in treatments of matched host–microbiome pairs, with rates approximately 50% and 250% higher in comparison to maximum growth rates of non‐matched host–microbiome pairs and germ‐free Sphagnum , respectively. We also found that the maximum growth rate of host–microbiome pairs was reached when treatment temperatures were close to the microbiome's native temperatures. Our study shows that Sphagnum 's growth acclimation to temperature is partially controlled by its constituent microbiome. Strong Sphagnum host–microbiome species specificity indicates the existence of underlying, unknown physiological mechanisms that may drive Sphagnum 's ability to acclimatize to elevated temperatures. Together with rapid acclimation of the microbiome to warming, these specific microbiome–plant associations have the potential to enhance peatland resilience in the face of climate change.

PREMISE:Hybridization is an important evolutionary process across all groups of embryophyte land plants, but relatively little is known about hybridization and introgression in plants with a dominant gametophyte life cycle stage. This paper focuses on hybridization between four closely related species of the moss genus Sphagnum. METHODS:Analyses utilized three types of molecular data: restriction-site-associated DNA sequencing (RADseq), RADseq-like data derived from in silico digestion of genome sequences, and species-specific barcode markers developed previously for this group. Sampling included 582 gametophytes from 79 collecting sites from 27° to 56°N. A range of analytical methods were employed: phylogeny reconstruction, genetic analyses using the program structure, demographic modeling, and comparative genomics. RESULTS:Gene flow was detected among all pairwise combinations of extant species and between ancestral lineages and those species. Hybridization between S. diabolicum and S. magniae was especially pronounced and plants in a regional zone from North Carolina to New Jersey were genetically admixed. Demographic analyses indicated that this admixture reflects hybridization. Introgressed SNPs were detected across all chromosomes, but introgressed SNPs fixed in genetically pure samples of the two species were concentrated on four autosomes: 2, 7, 14, and 19. Patterns of genomic admixture/introgression were significantly correlated with climate variation across collection sites within the hybrid zone. CONCLUSIONS:The genomic structure of plants in a regional hybrid zone between S. magniae and S. diabolicum was structured by climate adaptation and strengthens the value of this group for learning more about speciation and climate adaptation.

Sphagnum is emerging as a useful system for advancing knowledge at the interface between ecology and evolutionary biology. Here, we explore: the importance of the Sphagnum microbiome to ecosystem structure and function; the value of naturally occurring genetic variation within Sphagnum populations; and the ongoing process of speciation and ecological divergence in the genus. Recent advances in understanding the molecular genetics underpinning cyanobacteria associations with Sphagnum's living and hyaline cells make this a rich area for future research, including implications for carbon and nitrogen exchange. We review niche differentiation in Sphagnum, underlying functional traits, and phylogenetic conservation. More knowledge is needed about naturally occurring variation within Sphagnum species, including trait plasticity and variation between sexes, to explore broader issues such as the mechanisms underpinning metabolism and its consequences for microbiomes as well as how we can most effectively use Sphagnum in restoration and other ecological problem solving. We use newly resolved phylogenetic relationships within the S. magellanicum complex to illustrate its potential for studying ecologically driven speciation. Our review focuses on the unique challenges in using Sphagnum as an eco-evolutionary system but also offers insights into emerging questions across genetics, physiological traits, ecological function, and biogeochemical cycling.

Sphagnum magellanicum has historically been interpreted as a widespread species across both the Northern and Southern Hemispheres. Recent research, however, indicates that it comprises at least seven phylogenetic species, and that S. magellanicum s.str. is restricted to southern Argentina and Chile. Four species are recorded from North America and two of them, S. divinum and S. medium, are known to occur in Europe (and are typified by European collections). Here we assess European plants of this complex to test if two apparent North American endemics, S. diabolicum and S. magniae, occur in Europe, and document the genetic structure of European species of the complex, including gametophyte sex ratios and patterns of genetic diversity. We further assess evidence for gene flow between the species in Europe, and between North American and European plants of species that occur on both continents. Molecular data, especially ddRADseq, were used to assess genetic and phylogenetic patterns, and additional plants were identified with barcode markers to document European geographic distributions. The results indicate that S. diabolicum and S. magniae are endemic to North America. In Europe, S. divinum is more genetically diverse than S. medium. Sex ratios in both species did not depart from 50:50. Low levels of interspecific gene flow between the two species occur in Europe, as well as higher levels of gene flow between North American and European plants within S. divinum and S. medium. Overall, our results corroborate evidence that S. divinum and S. medium are phylogenetically distinct species and represent separate gene pools despite low levels of introgression.

Artificial intelligence (AI) for image-based herbarium specimen identification has thus far focused on plants that can be identified by eye. Here, we develop the first AI focused on identifying herbarium specimens of a bryophyte group, peat mosses in Sphagnum subgenus Sphagnum. These plants have substantial morphological plasticity, and confident identifications require time-consuming dissections and microscopy. We hypothesized that AI, using unmagnified low-resolution images, can (H1) identify species and (H2) discover novel morphological characters. We collected 4386 publicly available herbarium specimen images of all 10 North American species and imaged an additional 105 specimens with determinations verified by DNA and morphology. AI identification was generally successful with our newly formulated FireNetSEz model (68% AUCPR (area under the curve: precision recall)). We produced a reduced dataset (the five most imaged species) that we, the authors, could attempt. Our identifications took hours and were all lower-scoring than the AI. These H1 results show that AI can learn hard-to-identify botanical species without microscopy and outperform both generalist botanists and Sphagnum experts. Regarding H2, we found the AI focuses on edges of organs that humans often ignore. AI holds promise for hard botanical identifications and the potential to rapidly identify Sphagnum, which is important for studying peatlands that strongly impact climate.

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.

PREMISE:Shared geographical patterns of population genetic variation among related species is a powerful means to identify the historical events that drive diversification. The Sphagnum capillifolium complex is a group of closely related peat mosses within the Sphagnum subgenus Acutifolia and contains several circumboreal species whose ranges encompass both glaciated and unglaciated regions across the northern hemisphere. In this paper, we (1) inferred the phylogeny of subg. Acutifolia and (2) investigated patterns of population structure and genetic diversity among five circumboreal species within the S. capillifolium complex. METHODS:We generated RAD sequencing data from most species of the subg. Acutifolia and samples from across the distribution ranges of circumboreal species within the S. capillifolium complex. RESULTS:We resolved at least 14 phylogenetic clusters within the S. capillifolium complex. Five circumboreal species show some common patterns: One population system comprises plants in eastern North America and Europe, and another comprises plants in the Pacific Northwest or around the Beringian and Arctic regions. Alaska appears to be a hotspot for genetic admixture, genetic diversity, and sometimes endemic subclades. CONCLUSIONS:Our results support the hypothesis that populations of five circumboreal species within the S. capillifolium complex survived in multiple refugia during the last glacial maximum. Long-distance dispersal out of refugia, population bottlenecks, and possible adaptations to conditions unique to each refugium could have contributed to current geographic patterns. These results indicate the important role of historical events in shaping the complex population structure of plants with broad distribution ranges.

Premise: Sphagnum 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. Methods: Newly 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. Results: The 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 involved S. diabolicum vs. S. magniae. Conclusions: These 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 for S. diabolicum versus S. magniae could reflect incomplete speciation or hybridization. They comprise a valuable study system for additional work on climate adaptation.

Background and Aims New plant species can evolve through the reinforcement of reproductive isolation via local adaptation along habitat gradients. Peat mosses (Sphagnaceae) are an emerging model system for the study of evolutionary genomics and have well-documented niche differentiation among species. Recent molecular studies have demonstrated that the globally distributed species Sphagnum magellanicum is a complex of morphologically cryptic lineages that are phylogenetically and ecologically distinct. Here, we describe the architecture of genomic differentiation between two sister species in this complex known from eastern North America: the northern S. diabolicum and the largely southern S. magniae. Methods We sampled plant populations from across a latitudinal gradient in eastern North America and performed whole genome and restriction-site associated DNA sequencing. These sequencing data were then analyzed computationally. Key Results Using sliding-window population genetic analyses we find that differentiation is concentrated within ‘islands’ of the genome spanning up to 400 kb that are characterized by elevated genetic divergence, suppressed recombination, reduced nucleotide diversity and increased rates of non-synonymous substitution. Sequence variants that are significantly associated with genetic structure and bioclimatic variables occur within genes that have functional enrichment for biological processes including abiotic stress response, photoperiodism and hormone-mediated signalling. Demographic modelling demonstrates that these two species diverged no more than 225 000 generations ago with secondary contact occurring where their ranges overlap. Conclusions We suggest that this heterogeneity of genomic differentiation is a result of linked selection and reflects the role of local adaptation to contrasting climatic zones in driving speciation. This research provides insight into the process of speciation in a group of ecologically important plants and strengthens our predictive understanding of how plant populations will respond as Earth’s climate rapidly changes.

BACKGROUND AND AIMS:Sphagnum (peatmoss) comprises a moss (Bryophyta) clade with ~300-500 species. The genus has unparalleled ecological importance because Sphagnum-dominated peatlands store almost a third of the terrestrial carbon pool and peatmosses engineer the formation and microtopography of peatlands. Genomic resources for Sphagnum are being actively expanded, but many aspects of their biology are still poorly known. Among these are the degree to which Sphagnum species reproduce asexually, and the relative frequencies of male and female gametophytes in these haploid-dominant plants. We assess clonality and gametophyte sex ratios and test hypotheses about the local-scale distribution of clones and sexes in four North American species of the S. magellanicum complex. These four species are difficult to distinguish morphologically and are very closely related. We also assess microbial communities associated with Sphagnum host plant clones and sexes at two sites. METHODS:Four hundred and five samples of the four species, representing 57 populations, were subjected to restriction site-associated DNA sequencing (RADseq). Analyses of population structure and clonality based on the molecular data utilized both phylogenetic and phenetic approaches. Multi-locus genotypes (genets) were identified using the RADseq data. Sexes of sampled ramets were determined using a molecular approach that utilized coverage of loci on the sex chromosomes after the method was validated using a sample of plants that expressed sex phenotypically. Sex ratios were estimated for each species, and populations within species. Difference in fitness between genets was estimated as the numbers of ramets each genet comprised. Degrees of clonality [numbers of genets/numbers of ramets (samples)] within species, among sites, and between gametophyte sexes were estimated. Sex ratios were estimated for each species, and populations within species. Sphagnum-associated microbial communities were assessed at two sites in relation to Sphagnum clonality and sex. KEY RESULTS:All four species appear to engage in a mixture of sexual and asexual (clonal) reproduction. A single ramet represents most genets but two to eight ramets were dsumbers ansd text etected for some genets. Only one genet is represented by ramets in multiple populations; all other genets are restricted to a single population. Within populations ramets of individual genets are spatially clustered, suggesting limited dispersal even within peatlands. Sex ratios are male-biased in S. diabolicum but female-biased in the other three species, although significantly so only in S. divinum. Neither species nor males/females differ in levels of clonal propagation. At St Regis Lake (NY) and Franklin Bog (VT), microbial community composition is strongly differentiated between the sites, but differences between species, genets and sexes were not detected. Within S. divinum, however, female gametophytes harboured two to three times the number of microbial taxa as males. CONCLUSIONS:These four Sphagnum species all exhibit similar reproductive patterns that result from a mixture of sexual and asexual reproduction. The spatial patterns of clonally replicated ramets of genets suggest that these species fall between the so-called phalanx patterns, where genets abut one another but do not extensively mix because of limited ramet fragmentation, and the guerrilla patterns, where extensive genet fragmentation and dispersal result in greater mixing of different genets. Although sex ratios in bryophytes are most often female-biased, both male and female biases occur in this complex of closely related species. The association of far greater microbial diversity for female gametophytes in S. divinum, which has a female-biased sex ratio, suggests additional research to determine if levels of microbial diversity are consistently correlated with differing patterns of sex ratio biases.

Until a few years ago, Sphagnum magellanicum was understood to be a single widespread species with an intercontinental range. Recent work by Norwegian sphagnologists showed that S. magellanicum s.str. is restricted to southern South America and plants known as S. magellanicum in Europe should be referred to S. divinum and S. medium. In a separate publication, we showed that there are two additional major clades in eastern North America, and we describe them herein as S. diabolicum and S. magniae. These species are very hard to distinguish morphologically (and also from S. divinum and S. medium) but are distinct phylogenetically, ecologically and geographically, and are important units of biodiversity. Morphological variation within and between species is photographically documented.

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.

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 two Sphagnum species: S. divinum and S. angustifolium. Sphagnum genomes show no gene colinearity with any other reference genome to date, demonstrating that Sphagnum represents 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 of Sphagnum to sequester carbon in acidic peat bogs is mediated by interactions between sex, autosomes and environment.

Sphagnum peatmosses are fundamental members of peatland ecosystems, where they contribute to the uptake and long-term storage of atmospheric carbon. Warming threatens Sphagnum mosses and is known to alter the composition of their associated microbiome. Here, we use a microbiome transfer approach to test if microbiome thermal origin influences host plant thermotolerance. We leveraged an experimental whole-ecosystem warming study to collect field-grown Sphagnum, mechanically separate the associated microbiome and then transfer onto germ-free laboratory Sphagnum for temperature experiments. Host and microbiome dynamics were assessed with growth analysis, Chla fluorescence imaging, metagenomics, metatranscriptomics and 16S rDNA profiling. Microbiomes originating from warming field conditions imparted enhanced thermotolerance and growth recovery at elevated temperatures. Metagenome and metatranscriptome analyses revealed that warming altered microbial community structure in a manner that induced the plant heat shock response, especially the HSP70 family and jasmonic acid production. The heat shock response was induced even without warming treatment in the laboratory, suggesting that the warm-microbiome isolated from the field provided the host plant with thermal preconditioning. Our results demonstrate that microbes, which respond rapidly to temperature alterations, can play key roles in host plant growth response to rapidly changing environments.

Sphagnum magellanicum is one of two Sphagnum species for which a reference-quality genome exists to facilitate research in ecological genomics. Phylogenetic and comparative genomic analyses were conducted based on resequencing data from 48 samples and RADseq analyses based on 187 samples. We report herein that there are four clades/species within the S. magellanicum complex in eastern North America and that the reference genome belongs to Sphagnum divinum. The species exhibit tens of thousands (RADseq) to millions (resequencing) of fixed nucleotide differences. Two species, however, referred to informally as S. diabolicum and S. magni because they have not been formally described, are differentiated by only 100 (RADseq) to 1000 (resequencing) of differences. Introgression among species in the complex is demonstrated using D-statistics and f(4) ratios. One ecologically important functional trait, tissue decomposability, which underlies peat (carbon) accumulation, does not differ between segregates in the S. magellanicum complex, although previous research showed that many closely related Sphagnum species have evolved differences in decomposability/carbon sequestration. Phylogenetic resolution and more accurate species delimitation in the S. magellanicum complex substantially increase the value of this group for studying the early evolutionary stages of climate adaptation and ecological evolution more broadly.

A new propaguliferous moss species, Pohlia tibetana X.R.Wang & X.M.Shao (Mielichhoferiaceae), from Tibet, southwest China, is described. The new species differs most saliently from other species of Pohlia by its combination of slender plants, loosely attached leaves and axillary solitary, and dark red and flower-like gemmae. In this paper, the line drawings, photographs, habit of the new species are provided and a morphological comparison of it with the similar species is made.