Blanka Shaw

One species or at least eight? Delimitation and distribution of Frullania tamarisci (L.) Dumort. s. l. (Jungermanniopsida, Porellales) inferred from nuclear and chloroplast DNA markers.

Frullania tamarisci is usually regarded as a polymorphic, holarctic-Asian liverwort species with four allopatric subspecies [subsp. asagrayana, moniliata, nisquallensis and tamarisci]. This hypothesis is examined using a dataset including sequences of the nuclear internal transcribed spacer region and the plastid trnL-trnF and atpB-rbcL regions of 88 accessions of F. tamarisci and putatively related taxa. Maximum parsimony and maximum likelihood analyses indicate the presence of at least eight main lineages within F. tamarisci s. l. The long branches leading to the tip nodes of the different F. tamarisci s. l. clades and their partly sympatric distribution reinforce species rank. Within F. tamarisci s. l. we recognize the Asian F. moniliata, the western North American F. californica and F. nisquallensis, the eastern North American F. asagrayana, the eastern North American-European F. tamarisci s. str., the Macaronesian F. sergiae, and two newly identified European lineages assigned to as F. calcarifera and F. tamarisci var. azorica. The considerable sequence differences are not reflected in conspicuous morphological disparities, rendering F. tamarisci s. l. the most explicit example of a complex of semi-cryptic and cryptic liverwort species. The temperate Frullania clades of this study likely went through recent extinction and expansion processes as indicated by the bottleneck pattern of genetic diversity. Species from tropical regions or regions with an Atlantic climate usually contain several geographical lineages. Our findings support frequent short-distance migration, rare successful long-distance dispersal events, extinction and recolonization as an explanation for the range formation in these Frullania species.

Genetic variation in three Chinese peat mosses (Sphagnum) based on microsatellite markers, with primer information and analysis of ascertainment bias

Abstract Primer sequences are provided for amplification of 21 microsatellite-containing loci in Sphagnum. Although these primers were developed for species in Sphagnum section Subsecunda, they amplify microsatellite loci in most species that have been tested across the genus Sphagnum. Results are described from a survey of genetic variation in three species of Sphagnum collected in China: S. junghuhnianum in section Acutifolia, and S. palustre and S. imbricatum in section Sphagnum. Six and eight multilocus genotypes were detected within one population each of S. junghuhnianum and S. palustre, respectively. Four populations of S. imbricatum were sampled; they vary substantially in allele frequencies and in the amount of genetic diversity detected; overall, approximately 40% of the genetic variation sampled within S. imbricatum could be attributed to differentiation among populations. Microsatellite profiles indicate that S. palustre gametophytes are diploid whereas those of S. junghuhnianum and S. imbricatum are haploid.

Extant diversity of bryophytes emerged from successive post-Mesozoic diversification bursts

Unraveling the macroevolutionary history of bryophytes, which arose soon after the origin of land plants but exhibit substantially lower species richness than the more recently derived angiosperms, has been challenged by the scarce fossil record. Here we demonstrate that overall estimates of net species diversification are approximately half those reported in ferns and ∼30% those described for angiosperms. Nevertheless, statistical rate analyses on time-calibrated large-scale phylogenies reveal that mosses and liverworts underwent bursts of diversification since the mid-Mesozoic. The diversification rates further increase in specific lineages towards the Cenozoic to reach, in the most recently derived lineages, values that are comparable to those reported in angiosperms. This suggests that low diversification rates do not fully account for current patterns of bryophyte species richness, and we hypothesize that, as in gymnosperms, the low extant bryophyte species richness also results from massive extinctions.

Formalizing morphologically cryptic biological entities: New insights from DNA taxonomy, hybridization, and biogeography in the leafy liverwort Porella platyphylla (Jungermanniopsida, Porellales)

PREMISE OF THE STUDY Recognition and formalization of morphologically cryptic species is a major challenge to modern taxonomy. An extreme example in this regard is the Holarctic Porella platyphylla s.l. (P. platyphylla plus P. platyphylloidea). Earlier studies demonstrated the presence of three isozyme groups and two molecular lineages. The present investigation was carried out to elucidate the molecular diversity of P. platyphylla s.l. and the distribution of its main clades, and to evaluate evidence for the presence of one vs. several species. METHODS We obtained chloroplast (atpB-rbcL, trnL-trnF) and nuclear ribosomal (ITS) DNA sequences from 101 Porella accessions (P. platyphylla s.l., P. × baueri, P. cordaeana, P. bolanderi, plus outgroup species) to estimate the phylogeny using parsimony and likelihood analyses. To facilitate the adoption of Linnean nomenclature for molecular lineages, we chose a DNA voucher as epitype. KEY RESULTS Phylogenies derived from chloroplast vs. nuclear data were congruent except for P. platyphylla s.l., including a North American lineage that was placed sister to P. cordaeana in the chloroplast DNA phylogeny but sister to the Holarctic P. platyphylla s.str. in the nuclear DNA phylogeny. European and North American accessions of P. cordaeana and P. platyphylla form sister clades. CONCLUSIONS The genetic structure of P. platyphylla s.l. reflects morphologically cryptic or near cryptic speciation into Holarctic P. platyphylla s.str. and North American P. platyphylloidea. The latter species is possibly an ancient hybrid resulting from crossings of P. cordaeana and P. platyphylla s.str. and comprises several distinct molecular entities.

Morphologically cryptic biological species within the liverwort Frullania asagrayana

UNLABELLED PREMISE OF THE STUDY The Frullania tamarisci complex includes eight Holarctic liverwort species. One of these, F. asagrayana, is distributed broadly throughout eastern North America from Canada to the Gulf Coast. Preliminary genetic data suggested that the species includes two groups of populations. This study was designed to test whether the two groups are reproductively isolated biological species. • METHODS Eighty-eight samples from across the range of F. asagrayana, plus 73 samples from one population, were genotyped for 13 microsatellite loci. Sequences for two plastid loci and nrITS were obtained from 13 accessions. Genetic data were analyzed using coalescent models and Bayesian inference. • KEY RESULTS Frullania asagrayana is sequence-invariant at the two plastid loci and ITS2, but two clear groups were resolved by microsatellites. The two groups are largely reproductively isolated, but there is a low level of gene flow from the southern to the northern group. No gene flow was detected in the other direction. A local population was heterogeneous but displayed strong genetic structure. • CONCLUSIONS The genetic structure of F. asagrayana in eastern North America reflects morphologically cryptic differentiation between reproductively isolated groups of populations, near-panmixis within groups, and clonal propagation at local scales. Reproductive isolation between groups that are invariant at the level of nucleotide sequences shows that caution must be exercised in making taxonomic and evolutionary inferences from reciprocal monophyly (or lack thereof) between putative species.

Peatmoss (Sphagnum) diversification associated with Miocene Northern Hemisphere climatic cooling

Global climate changes sometimes spark biological radiations that can feed back to effect significant ecological impacts. Northern Hemisphere peatlands dominated by living and dead peatmosses (Sphagnum) harbor almost 30% of the global soil carbon pool and have functioned as a net carbon sink throughout the Holocene, and probably since the late Tertiary. Before that time, northern latitudes were dominated by tropical and temperate plant groups and ecosystems. Phylogenetic analyses of mosses (phylum Bryophyta) based on nucleotide sequences from the plastid, mitochondrial, and nuclear genomes indicate that most species of Sphagnum are of recent origin (ca. <20 Ma). Sphagnum species are not only well-adapted to boreal peatlands, they create the conditions that promote development of peatlands. The recent radiation that gave rise to extant diversity of peatmosses is temporally associated with Miocene climatic cooling in the Northern Hemisphere. The evolution of Sphagnum has had profound influences on global biogeochemistry because of the unique biochemical, physiological, and morphological features of these plants, both while alive and after death.

Phylogeny of the leafy liverwort Ptilidium: Cryptic speciation and shared haplotypes between the Northern and Southern Hemispheres

The small, phylogenetically isolated liverwort genus Ptilidium has been regarded as of cool-Gondwanic origin with the bipolar, terrestrial Ptilidium ciliare giving rise to the Northern Hemisphere epiphytes Ptilidium pulcherrimum and Ptilidium californicum. This hypothesis is examined using a dataset including three chloroplast DNA regions from 134 Ptilidium accessions and one accession each of its closest relatives Trichocoleopsis and Neotrichocolea. Maximum likelihood and parsimony analyses point to a close relationship between P. ciliare and P. pulcherrimum, whereas P. californicum is placed sister to the remainder of the genus, separated by a long branch. Haplotype analysis and our phylogeny indicate the presence of Southern Hemisphere haplotypes of P. ciliare in the Northern Hemisphere, and shared haplotypes of P. ciliare and P. pulcherrimum between Europe and North America. Based on our findings, we reject the Gondwana-scenario and propose recent long distance dispersal as an explanation for the bipolar disjunct range. Ptilidium ciliare is resolved as paraphyletic with P. pulcherrimum nested within it. An isolated Ptilidium lineage with the morphology of P. ciliare from the Himalaya region likely represents a hitherto unrecognized cryptic species. Ptilidium pulcherrimum splits into a Japanese clade and a clade with accessions from Europe and North America.

Newly resolved relationships in an early land plant lineage: Bryophyta class Sphagnopsida (peat mosses)

UNLABELLED PREMISE OF THE STUDY The Sphagnopsida, an early-diverging lineage of mosses (phylum Bryophyta), are morphologically and ecologically unique and have profound impacts on global climate. The Sphagnopsida are currently classified in two genera, Sphagnum (peat mosses) with some 350-500 species and Ambuchanania with one species. An analysis of phylogenetic relationships among species and genera in the Sphagnopsida were conducted to resolve major lineages and relationships among species within the Sphagnopsida. • METHODS Phylogenetic analyses of nucleotide sequences from the nuclear, plastid, and mitochondrial genomes (11 704 nucleotides total) were conducted and analyzed using maximum likelihood and Bayesian inference employing seven different substitution models of varying complexity. • KEY RESULTS Phylogenetic analyses resolved three lineages within the Sphagnopsida: (1) Sphagnum sericeum, (2) S. inretortum plus Ambuchanania leucobryoides, and (3) all remaining species of Sphagnum. Sister group relationships among these three clades could not be resolved, but the phylogenetic results indicate that the highly divergent morphology of A. leucobryoides is derived within the Sphagnopsida rather than plesiomorphic. A new classification is proposed for class Sphagnopsida, with one order (Sphagnales), three families, and four genera. • CONCLUSIONS The Sphagnopsida are an old lineage within the phylum Bryophyta, but the extant species of Sphagnum represent a relatively recent radiation. It is likely that additional species critical to understanding the evolution of peat mosses await discovery, especially in the southern hemisphere.

A phylogenetic delimitation of the "Sphagnum subsecundum complex" (Sphagnaceae, Bryophyta).

A seemingly obvious but sometimes overlooked premise of any evolutionary analysis is delineating the group of taxa under study. This is especially problematic in some bryophyte groups because of morphological simplicity and convergence. This research applies information from nucleotide sequences for eight plastid and nuclear loci to delineate a group of northern hemisphere peat moss species, the so-called Sphagnum subsecundum complex, which includes species known to be gametophytically haploid or diploid (i.e., sporophytically diploid-tetraploid). Despite the fact that S. subsecundum and several species in the complex have been attributed disjunct ranges that include all major continents, phylogenetic analyses suggest that the group is actually restricted to Europe and eastern North America. Plants from western North America, from California to Alaska, which are morphologically similar to species of the S. subsecundum complex in eastern N. America and Europe, actually belong to a different deep clade within Sphagnum section Subsecunda. One species often considered part of the S. subsecundum complex, S. contortum, likely has a reticulate history involving species in the two deepest clades within section Subsecunda. Nucleotide sequences have a strong geographic structure across the section Subsecunda, but shallow tip clades suggest repeated long-distance dispersal in the section as well.

NORTH AMERICAN ORIGIN AND RECENT EUROPEAN ESTABLISHMENTS OF THE AMPHI-ATLANTIC PEAT MOSS SPHAGNUM ANGERMANICUM

Genetic and morphological similarity between populations separated by large distances may be caused by frequent long‐distance dispersal or retained ancestral polymorphism. The frequent lack of differentiation between disjunct conspecific moss populations on different continents has traditionally been explained by the latter model, and has been cited as evidence that many or most moss species are extremely ancient and slowly diverging. We have studied intercontinental differentiation in the amphi‐Atlantic peat moss Sphagnum angermanicum using 23 microsatellite markers. Two major genetic clusters are found, both of which occur throughout the distributional range. Patterns of genetic structuring and overall migration patterns suggest that the species probably originated in North America, and seems to have been established twice in Northern Europe during the past 40,000 years. We conclude that similarity between S. angermanicum populations on different continents is not the result of ancient vicariance and subsequent stasis. Rather, the observed pattern can be explained by multiple long‐distance dispersal over limited evolutionary time. The genetic similarity can also partly be explained by incomplete lineage sorting, but this appears to be caused by the short time since separation. Our study adds to a growing body of evidence suggesting that Sphagnum, constituting a significant part of northern hemisphere biodiversity, may be more evolutionary dynamic than previously assumed.