Comprehensive phylogenomic time tree of bryophytes reveals deep relationships and uncovers gene incongruences in the last 500 million years of diversification.

PREMISE: Bryophytes form a major component of terrestrial plant biomass, structuring ecological communities in all biomes. Our understanding of the evolutionary history of hornworts, liverworts, and mosses has been significantly reshaped by inferences from molecular data, which have highlighted extensive homoplasy in various traits and repeated bursts of diversification. However, the timing of key events in the phylogeny, patterns, and processes of diversification across bryophytes remain unclear. METHODS: Using the GoFlag probe set, we sequenced 405 exons representing 228 nuclear genes for 531 species from 52 of the 54 orders of bryophytes. We inferred the species phylogeny from gene tree analyses using concatenated and coalescence approaches, assessed gene conflict, and estimated the timing of divergences based on 29 fossil calibrations. RESULTS: The phylogeny resolves many relationships across the bryophytes, enabling us to resurrect five liverwort orders and recognize three more and propose 10 new orders of mosses. Most orders originated in the Jurassic and diversified in the Cretaceous or later. The phylogenomic data also highlight topological conflict in parts of the tree, suggesting complex processes of diversification that cannot be adequately captured in a single gene-tree topology. CONCLUSIONS: We sampled hundreds of loci across a broad phylogenetic spectrum spanning at least 450 Ma of evolution; these data resolved many of the critical nodes of the diversification of bryophytes. The data also highlight the need to explore the mechanisms underlying the phylogenetic ambiguity at specific nodes. The phylogenomic data provide an expandable framework toward reconstructing a comprehensive phylogeny of this important group of plants.

Plant migration under long-lasting hyperaridity - phylogenomics unravels recent biogeographic history in one of the oldest deserts on Earth.

The post-Miocene climatic histories of arid environments have been identified as key drivers of dispersal and diversification. Here, we investigate how climatic history correlates with the historical biogeography of the Atacama Desert genus Cristaria (Malvaceae). We analyze phylogenetic relationships and historical biogeography by using next-generation sequencing (NGS), molecular clock dating, Dispersal Extinction Cladogenesis and Bayesian sampling approaches. We employ a novel way to identify biogeographically meaningful regions as well as a rarely utilized program permitting the use of dozens of ancestral areas. Partial incongruence between the established taxonomy and our phylogenetic data argue for a complex historical biogeography with repeated introgression and incomplete lineage sorting. Cristaria originated in the central southern part of the Atacama Desert, from there the genus colonized other areas from the late Miocene onwards. The more recently diverged lineages appear to have colonized different habitats in the Atacama Desert during pluvial phases of the Pliocene and early Pleistocene. We show that NGS combined with near-comprehensive sampling can provide an unprecedented degree of phylogenetic resolution and help to correlate the historical biogeography of plant communities with cycles of arid and pluvial phases.

The evolution and biogeographic history of epiphytic thalloid liverworts.

Among liverworts, the epiphytic lifestyle is not only present in leafy forms but also in thalloid liverworts, which so far has received little attention in evolutionary and biogeographical studies. Metzgeria, with about 107 species worldwide, is the only genus of thalloid liverworts that comprises true epiphytes. In the present study, we provide the first comprehensive molecular phylogeny, including estimated divergence times and ancestral ranges of this genus. Analyses are based on a plastid marker dataset representing about half of the Metzgeria species diversity. We show for the first time with molecular data that Austrometzgeria is indeed a member of Metzgeria and that two morpho-species M. furcata and M. leptoneura are not monophyletic, but rather represent geographically well-defined clades. Our analyses indicate that Metzgeria started to diversify in the Cretaceous in an area encompassing today's South America and Australasia. Thus, Metzgeria is one of the few known epiphytic liverwort genera whose biogeographic history was directly shaped by Gondwana vicariance. Subsequent dispersal events in the Cenozoic resulted in the colonization of Asia, Africa, North America, and Europe and led to today's worldwide distribution of its species. We also provide the first reliable stem age estimate for Metzgeria due to the inclusion of its sister taxon Vandiemenia in our dating analyses. Additionally, this stem age estimate of about 240 million years most likely marks the starting point of a transition from a terrestrial to an epiphytic lifestyle in thalloid liverworts of the Metzgeriales. We assume that the Cretaceous Terrestrial Revolution played a key role in the evolution of epiphytic thalloid liverworts similar to that known for leafy liverworts.

Quaternary diversification of a columnar cactus in the driest place on earth.

PREMISE: The cactus family (Cactaceae) is a speciose lineage with an almost entirely New World distribution. The genus Eulychnia with eight currently recognized species is endemic to the Atacama and Peruvian Deserts. Here we investigated the phylogeny of this group based on a complete taxon sampling to elucidate species delimitation and biogeographic history of the genus. METHODS: A family-wide Bayesian molecular clock dating based on plastid sequence data was conducted to estimate the age of Eulychnia and its divergence from its sister genus Austrocactus. A second data set obtained from genotyping by sequencing (GBS) was analyzed, using the family-wide age estimate as a secondary calibration to date the GBS phylogeny using a penalized likelihood approach. Ancestral ranges were inferred employing the dispersal extinction cladogenesis approach. RESULTS: Our GBS phylogeny of Eulychnia was fully resolved with high support values nearly throughout the phylogeny. The split from Austrocactus occurred in the late Miocene, and Eulychnia diversified during the early Quaternary. Three lineages were retrieved: Eulychnia ritteri from Peru is sister to all Chilean species, which in turn fall into two sister clades of three and four species, respectively. Diversification in the Chilean clades started in the early Pleistocene. Eulychnia likely originated at the coastal range of its distribution and colonized inland locations several times. CONCLUSIONS: Diversification of Eulychnia during the Pleistocene coincides with long periods of hyperaridity alternated with pluvial phases. Hyperaridity caused habitat fragmentation, ultimately leading to speciation and resulting in the current allopatric distribution of taxa.

A multilocus phylogeny of the non-photosynthetic parasitic plant Cistanche (Orobanchaceae) refutes current taxonomy and identifies four major morphologically distinct clades.

Phylogenetic relationships of and within non-photosynthetic parasitic lineages are notoriously poorly known, which negatively affects our understanding of parasitic plants. This is also the case for Cistanche (Orobanchaceae), an Old World genus with about two dozen species, whose relationships have not yet been addressed using molecular phylogenetic approaches. Here we infer phylogenetic relationships within the genus, employing a taxonomically and geographically broad sampling covering all previously distinguished infrageneric groups and most of the currently recognized species. A combined matrix of three plastid markers (trnL-trnF, including the trnL intron and the intergenic spacer (IGS), trnS-trnfM IGS and psbA-trnH IGS) and one nuclear marker (ITS) was analyzed using maximum parsimony, maximum likelihood and Bayesian inference. Cistanche falls into four well-supported and geographically differentiated clades: East Asian Clade, Northwest African Clade, Southwest Asian Clade and Widespread Clade. Of those, only the East Asian Clade corresponds to a previously recognized taxonomic section, whereas the others either contain members of two or three sections (Widespread Clade and Southwest Asian Clade, respectively) or have not been taxonomically recognized so far (Northwest African Clade). Whereas the Southwest Asian Clade exhibits strong phylogenetic structure among and partly within species (the East Asian Clade and the Northwest African Clade are monospecific), phylogenetic resolution within the Widespread Clade is often low and hampered by discrepancies between nuclear and plastid markers. Both molecular and morphological data indicate that species diversity in Cistanche is currently underestimated.

Morphology, geographic distribution, and host preferences are poor predictors of phylogenetic relatedness in the mistletoe genus Viscum L.

Besides their alleged therapeutic effects, mistletoes of the genus Viscum L. (Viscaceae) are keystone species in many ecosystems across Europe, Africa, Asia and Australia because of their complex faunal interactions. We here reconstructed the evolutionary history of Viscum based on plastid and nuclear DNA sequence data. We obtained a highly resolved phylogenetic tree with ten well-supported clades, which we used to understand the spatio-temporal evolution of these aerial parasites and evaluate the contribution of reproductive switches and shifts in host ranges to their distribution and diversification. The genus Viscum originated in the early Eocene in Africa and appeared to have diversified mainly through geographic isolation, in several cases apparently coinciding with shifts in host preferences. During its evolution, switches in the reproductive mode from ancestral dioecy to monoecy imply an important role in the long-distance dispersal of the parasites from Africa to continental Asia and Australia. We also observed multiple cases of photosynthetic surface reduction (evolution of scale leaves) within the genus, probably indicative of increasing specialization associated with the parasitic lifestyle. Even compared with other parasitic angiosperms, where more host generalists than specialists exist, Viscum species are characterized by extraordinarily broad host ranges. Specialization on only a few hosts from a single family or order occurs rarely and is restricted mostly to very recently evolved lineages. The latter mostly derive from or are closely related to generalist parasites, implying that niche shifting to a new host represents an at least temporary evolutionary advantage in Viscum.

Mechanistic model of evolutionary rate variation en route to a nonphotosynthetic lifestyle in plants.

Because novel environmental conditions alter the selection pressure on genes or entire subgenomes, adaptive and nonadaptive changes will leave a measurable signature in the genomes, shaping their molecular evolution. We present herein a model of the trajectory of plastid genome evolution under progressively relaxed functional constraints during the transition from autotrophy to a nonphotosynthetic parasitic lifestyle. We show that relaxed purifying selection in all plastid genes is linked to obligate parasitism, characterized by the parasite's dependence on a host to fulfill its life cycle, rather than the loss of photosynthesis. Evolutionary rates and selection pressure coevolve with macrostructural and microstructural changes, the extent of functional reduction, and the establishment of the obligate parasitic lifestyle. Inferred bursts of gene losses coincide with periods of relaxed selection, which are followed by phases of intensified selection and rate deceleration in the retained functional complexes. Our findings suggest that the transition to obligate parasitism relaxes functional constraints on plastid genes in a stepwise manner. During the functional reduction process, the elevation of evolutionary rates reaches several new rate equilibria, possibly relating to the modified protein turnover rates in heterotrophic plastids.

Pulling the sting out of nettle systematics - A comprehensive phylogeny of the genus Urtica L. (Urticaceae).

The genus Urtica L. is subcosmopolitan, found on all continents (except Antarctica) and most extratropical islands and ranges from Alaska to Patagonia, Spitzbergen to the Cape and Camtschatka to the subantarctic islands. However, throughout its geographical range morphologically nearly indistinguishable species are found alongside morphologically quite disparate species, with the overall diversity of morphological characters extremely limited. The systematics of Urtica have puzzled scientists for the past 200years and no single comprehensive attempt at understanding infrageneric relationships has been published in the past, nor are species delimitations unequivocally established. We here provide the first comprehensive phylogeny of the genus including 61 of the 63 species recognized, represented by 144 ingroup accessions and 14 outgroup taxa. The markers ITS1-5.8S-ITS2, psbA-trnH intergenic spacer, trnL-trnF and trnS-trnG are used. The phylogeny is well resolved. The eastern Asian Zhengyia shennongensis T. Deng, D.G. Zhang & H. Sun is retrieved as sister to Urtica. Within Urtica, a clade comprising the western Eurasian species U. pilulifera L. and U. neubaueri Chrtek is sister to all other species of the genus. The phylogenetic analyses retrieve numerous well-supported clades, suggesting previously unsuspected relationships and implying that classically used taxonomic characters such as leaf morphology and growth habit are highly homoplasious. Species delimitation is problematical, and several accessions assigned to Urtica dioica L. (as subspecies) are retrieved in widely different places in the phylogeny. The genus seems to have undergone numerous dispersal-establishment events both between continents and onto different islands. Three recent species radiations are inferred, one in America centered in the Andes, one in New Zealand, and one in northern Eurasia which includes Urtica dioica s.str. sensu Henning et al. (2014). The present study provides the basis of a critical re-examination of species limits and taxonomy, but also of the dispersal ecology of this widespread plant group and an in-depth study of the three clades with recent radiations.

Mechanisms of functional and physical genome reduction in photosynthetic and nonphotosynthetic parasitic plants of the broomrape family.

Nonphotosynthetic plants possess strongly reconfigured plastomes attributable to convergent losses of photosynthesis and housekeeping genes, making them excellent systems for studying genome evolution under relaxed selective pressures. We report the complete plastomes of 10 photosynthetic and nonphotosynthetic parasites plus their nonparasitic sister from the broomrape family (Orobanchaceae). By reconstructing the history of gene losses and genome reconfigurations, we find that the establishment of obligate parasitism triggers the relaxation of selective constraints. Partly because of independent losses of one inverted repeat region, Orobanchaceae plastomes vary 3.5-fold in size, with 45 kb in American squawroot (Conopholis americana) representing the smallest plastome reported from land plants. Of the 42 to 74 retained unique genes, only 16 protein genes, 15 tRNAs, and four rRNAs are commonly found. Several holoparasites retain ATP synthase genes with intact open reading frames, suggesting a prolonged function in these plants. The loss of photosynthesis alters the chromosomal architecture in that recombinogenic factors accumulate, fostering large-scale chromosomal rearrangements as functional reduction proceeds. The retention of DNA fragments is strongly influenced by both their proximity to genes under selection and the co-occurrence with those in operons, indicating complex constraints beyond gene function that determine the evolutionary survival time of plastid regions in nonphotosynthetic plants.

Establishment of Anthoceros agrestis as a model species for studying the biology of hornworts.

BACKGROUND: Plants colonized terrestrial environments approximately 480 million years ago and have contributed significantly to the diversification of life on Earth. Phylogenetic analyses position a subset of charophyte algae as the sister group to land plants, and distinguish two land plant groups that diverged around 450 million years ago - the bryophytes and the vascular plants. Relationships between liverworts, mosses hornworts and vascular plants have proven difficult to resolve, and as such it is not clear which bryophyte lineage is the sister group to all other land plants and which is the sister to vascular plants. The lack of comparative molecular studies in representatives of all three lineages exacerbates this uncertainty. Such comparisons can be made between mosses and liverworts because representative model organisms are well established in these two bryophyte lineages. To date, however, a model hornwort species has not been available. RESULTS: Here we report the establishment of Anthoceros agrestis as a model hornwort species for laboratory experiments. Axenic culture conditions for maintenance and vegetative propagation have been determined, and treatments for the induction of sexual reproduction and sporophyte development have been established. In addition, protocols have been developed for the extraction of DNA and RNA that is of a quality suitable for molecular analyses. Analysis of haploid-derived genome sequence data of two A. agrestis isolates revealed single nucleotide polymorphisms at multiple loci, and thus these two strains are suitable starting material for classical genetic and mapping experiments. CONCLUSIONS: Methods and resources have been developed to enable A. agrestis to be used as a model species for developmental, molecular, genomic, and genetic studies. This advance provides an unprecedented opportunity to investigate the biology of hornworts.

Floral development of Sabia (Sabiaceae): evidence for the derivation of pentamery from a trimerous ancestry.

UNLABELLED: • PREMISE OF THE STUDY: Flowers of Sabiaceae diverge from basal eudicots in combining pentamery with superposed whorls of sepals, petals, and stamens and are therefore crucial in understanding origins of core eudicot flowers. Different hypotheses are tested using floral developmental evidence, whether the pentamerous flower is derived from a spiral, trimerous, or dimerous progenitor.• METHODS: The floral development of two species of Sabia was investigated with the scanning electron microscope to understand their unusual floral morphology and the origin of pentamery.• KEY RESULTS: The species show major developmental differences in their inflorescence morphology and organ initiation sequence. In S. limoniacea, flowers are subtended by a pherophyll preceding two prophylls, one of which encloses a younger flower; floral organs arise in a continuous spiral sequence without interruption between different organs. The ovary is oriented in an oblique-median position. In S. japonica, one prophyll replaces one of the sepals, and there is a disruption in the spiral sequence. As a result, the ovary is inserted more or less transversally.• CONCLUSIONS: The flower of Sabiaceae is structurally best interpreted as derived from a trimerous progenitor, and a derivation from a dimerous or spiral progenitor is less likely. One organ of each median adaxial whorl is interpreted as lost (from K3+3 C3+3 A3+3 G3 to K3+2 C3+2 A3+2 G2). The number of sepals is variable as pherophylls, prophylls, and sepals cannot be distinguished by shape and intergrade with each other. The floral organization of Sabia is reminiscent of trimerous Ranunculales and supports an earlier divergence of Sabiaceae relative to Proteales.

Stereoisomeric Composition of Natural Myrtucommulone A.

Myrtucommulone A (MC A) (1), isolated from Myrtus communis (myrtle), shows the same pharmacological activity for inhibition of inflammation and induction of apoptosis as synthetic MC A, which consists of three stereoisomers, i.e., two enantiomers and one meso form. This led to the question of whether the natural MC A is a pure stereoisomer or a mixture of stereoisomers. The specific rotation and electronic circular dichroism (ECD) data of natural MC A (1) as well as of a pentacyclic derivative 4 revealed that naturally occurring MC A (1) consists of the racemate and the meso form in a 1:1 ratio. A probable precursor of MC A (1), nor-semimyrtucommulone (5), was also isolated from myrtle as a racemate. The absolute configurations of the enantiomers of 1 and 5 were determined using a combination of experimental and quantum-chemical calculated ECD spectra.

Molecular evidence for convergent evolution and allopolyploid speciation within the Physcomitrium-Physcomitrella species complex.

BACKGROUND: The moss Physcomitrella patens (Hedw.) Bruch & Schimp. is an important experimental model system for evolutionary-developmental studies. In order to shed light on the evolutionary history of Physcomitrella and related species within the Funariaceae, we analyzed the natural genetic diversity of the Physcomitrium-Physcomitrella species complex. RESULTS: Molecular analysis of the nuclear single copy gene BRK1 reveals that three Physcomitrium species feature larger genome sizes than Physcomitrella patens and encode two expressed BRK1 homeologs (polyploidization-derived paralogs), indicating that they may be allopolyploid hybrids. Phylogenetic analyses of BRK1 as well as microsatellite simple sequence repeat (SSR) data confirm a polyphyletic origin for three Physcomitrella lineages. Differences in the conservation of mitochondrial editing sites further support hybridization and cryptic speciation within the Physcomitrium-Physcomitrella species complex. CONCLUSIONS: We propose a revised classification of the previously described four subspecies of Physcomitrella patens into three distinct species, namely Physcomitrella patens, Physcomitrella readeri and Physcomitrella magdalenae. We argue that secondary reduction of sporophyte complexity in these species is due to the establishment of an ecological niche, namely spores resting in mud and possible spore dispersal by migratory birds. Besides the Physcomitrium-Physcomitrella species complex, the Funariaceae are host to their type species, Funaria hygrometrica, featuring a sporophyte morphology which is more complex. Their considerable developmental variation among closely related lineages and remarkable trait evolution render the Funariaceae an interesting group for evolutionary and genetic research.

Organellar-genome analyses from the lycophyte genus Isoetes L. show one of the highest frequencies of RNA editing in land plants.

RNA editing is a post-transcriptional process that challenges the central dogma of molecular biology by modifying RNA sequences, introducing nucleotide changes at specific sites, and generating functional diversity beyond the genomic code, especially when it concerns organellar transcripts. In plants, this phenomenon is widespread, but its extent varies significantly among species and organellar genomes. Among land plants, the heterosporous lycophytes (i.e., Isoetes and Selaginella) stand out for their exceptionally high numbers of RNA-editing sites, despite their morphological stasis and ancient lineage. In this study, we explore the complete set of organellar protein-coding genes in the aquatic plant group Isoetes, providing a detailed analysis of RNA editing in both the mitochondrial and plastid genomes. Our findings reveal a remarkable abundance of RNA editing, particularly in the mitochondrial genome, with thousands of editing sites identified. Interestingly, the majority of these edits result in non-silent substitutions, suggesting a role in fine-tuning protein structure and function. Furthermore, we observe a consistent trend of increased hydrophobicity in membrane-bound proteins, supporting the notion that RNA editing may confer a selective advantage by preserving gene functionality in Isoetes. The conservation of highly edited RNA sequences over millions of years underscores the evolutionary significance of RNA editing. Additionally, the study sheds light on the dynamic nature of RNA editing, with shared editing sites reflecting common ancestry whereas exclusive edits matching more recent radiation events within the genus. This work advances our understanding of the intricate interplay between RNA editing, adaptation, and evolution in land plants and highlights the unique genomic features of Isoetes, providing a foundation for further investigations into the functional consequences of RNA editing in this enigmatic plant lineage.

Land plant evolutionary timeline: gene effects are secondary to fossil constraints in relaxed clock estimation of age and substitution rates.

PREMISE OF THE STUDY: Land plants play an essential role in the evolution of terrestrial life. Their time of origin and diversification is fundamental to understanding the evolution of life on land. We investigated the timing and the rate of molecular evolution of land plants, evaluating the effects of different types of molecular data, including temporal information from fossils, and using different molecular clock methods. • METHODS: Ages and absolute rates were estimated independently with two substitutionally different data sets: a highly conserved 4-gene data set and matK, a fast-evolving gene. The vascular plant backbone and the crown nodes of all major lineages were calibrated with fossil-derived ages. Dates and absolute rates were estimated while including or excluding the calibrations and using two relaxed clocks that differ in their implementation of temporal autocorrelation. • KEY RESULTS: Land plants diverged from streptophyte alga 912 (870-962) million years ago (Mya) but diversified into living lineages 475 (471-480) Mya. Ages estimated for all major land-plant lineages agree with their fossil record, except for angiosperms. Different genes estimated very similar ages and correlated absolute rates across the tree. Excluding calibrations resulted in the greatest age differences. Different relaxed clocks provided similar ages, but different and uncorrelated absolute rates. • CONCLUSIONS: Whole-genome rate accelerations or decelerations may underlie the similar ages and correlated absolute rates estimated with different genes. We suggest that pronounced substitution rate changes around the angiosperm crown node may represent a challenge for relaxed clocks to model adequately.

Tillandsia landbeckii phyllosphere and laimosphere as refugia for bacterial life in a hyperarid desert environment.

BACKGROUND: The lack of water is a major constraint for microbial life in hyperarid deserts. Consequently, the abundance and diversity of microorganisms in common habitats such as soil are strongly reduced, and colonization occurs primarily by specifically adapted microorganisms that thrive in particular refugia to escape the harsh conditions that prevail in these deserts. We suggest that plants provide another refugium for microbial life in hyperarid deserts. We studied the bacterial colonization of Tillandsia landbeckii (Bromeliaceae) plants, which occur in the hyperarid regions of the Atacama Desert in Chile, one of the driest and oldest deserts on Earth. RESULTS: We detected clear differences between the bacterial communities being plant associated to those of the bare soil surface (PERMANOVA, R2 = 0.187, p = 0.001), indicating that Tillandsia plants host a specific bacterial community, not only dust-deposited cells. Moreover, the bacterial communities in the phyllosphere were distinct from those in the laimosphere, i.e., on buried shoots (R2 = 0.108, p = 0.001), indicating further habitat differentiation within plant individuals. The bacterial taxa detected in the phyllosphere are partly well-known phyllosphere colonizers, but in addition, some rather unusual taxa (subgroup2 Acidobacteriae, Acidiphilum) and insect endosymbionts (Wolbachia, "Candidatus Uzinura") were found. The laimosphere hosted phyllosphere-associated as well as soil-derived taxa. The phyllosphere bacterial communities showed biogeographic patterns across the desert (R2 = 0.331, p = 0.001). These patterns were different and even more pronounced in the laimosphere (R2 = 0.467, p = 0.001), indicating that different factors determine community assembly in the two plant compartments. Furthermore, the phyllosphere microbiota underwent temporal changes (R2 = 0.064, p = 0.001). CONCLUSIONS: Our data demonstrate that T. landbeckii plants host specific bacterial communities in the phyllosphere as well as in the laimosphere. Therewith, these plants provide compartment-specific refugia for microbial life in hyperarid desert environments. The bacterial communities show biogeographic patterns and temporal variation, as known from other plant microbiomes, demonstrating environmental responsiveness and suggesting that bacteria inhabit these plants as viable microorganisms. Video Abstract.

Liverworts show a globally consistent mid-elevation richness peak.

The study of elevational gradients allows to draw conclusions on the factors and mechanisms determining patterns in species richness distribution. Several earlier studies investigated liverwort diversity on single or few elevational transects. However, a comprehensive survey of the elevational distribution patterns of liverwort richness and their underlying factors is lacking so far. This study's purpose was to fill this gap by compiling an extensive data set of liverwort elevational patterns encompassing a broad diversity of mountains and mountain ranges around the world. Using polynomial regression analyses, we found a prevalence of hump-shaped richness patterns (19 of 25 gradients), where liverwort species richness peaked at mid-elevation and decreased towards both ends of the gradient. Against our expectation and unlike in other plant groups, in liverworts, this pattern also applies to elevational gradients at mid-latitudes in temperate climates. Indeed, relative elevation, calculated as the percentage of the elevational range potentially inhabited by liverworts, was the most powerful predictor for the distribution of liverwort species richness. We conclude from these results that the admixture of low- and high-elevation liverwort floras, in combination with steep ecological gradients, leads to a mid-elevation floristic turnover shaping elevational patterns of liverwort diversity. Our analyses further detected significant effects of climatic variables (temperature of the warmest month, potential evapotranspiration, and precipitation of the warmest month) in explaining elevational liverwort richness patterns. This indicates that montane liverwort diversity is restricted by high temperatures and subsequent low water availability especially towards lower elevations, which presumably will lead to serious effects by temperature shifts associated with global warming.

The evolution of the plastid chromosome in land plants: gene content, gene order, gene function.

This review bridges functional and evolutionary aspects of plastid chromosome architecture in land plants and their putative ancestors. We provide an overview on the structure and composition of the plastid genome of land plants as well as the functions of its genes in an explicit phylogenetic and evolutionary context. We will discuss the architecture of land plant plastid chromosomes, including gene content and synteny across land plants. Moreover, we will explore the functions and roles of plastid encoded genes in metabolism and their evolutionary importance regarding gene retention and conservation. We suggest that the slow mode at which the plastome typically evolves is likely to be influenced by a combination of different molecular mechanisms. These include the organization of plastid genes in operons, the usually uniparental mode of plastid inheritance, the activity of highly effective repair mechanisms as well as the rarity of plastid fusion. Nevertheless, structurally rearranged plastomes can be found in several unrelated lineages (e.g. ferns, Pinaceae, multiple angiosperm families). Rearrangements and gene losses seem to correlate with an unusual mode of plastid transmission, abundance of repeats, or a heterotrophic lifestyle (parasites or myco-heterotrophs). While only a few functional gene gains and more frequent gene losses have been inferred for land plants, the plastid Ndh complex is one example of multiple independent gene losses and will be discussed in detail. Patterns of ndh-gene loss and functional analyses indicate that these losses are usually found in plant groups with a certain degree of heterotrophy, might rendering plastid encoded Ndh1 subunits dispensable.

Restless 5S: the re-arrangement(s) and evolution of the nuclear ribosomal DNA in land plants.

Among eukaryotes two types of nuclear ribosomal DNA (nrDNA) organization have been observed. Either all components, i.e. the small ribosomal subunit, 5.8S, large ribosomal subunit, and 5S occur tandemly arranged or the 5S rDNA forms a separate cluster of its own. Generalizations based on data derived from just a few model organisms have led to a superimposition of structural and evolutionary traits to the entire plant kingdom asserting that plants generally possess separate arrays. This study reveals that plant nrDNA organization into separate arrays is not a distinctive feature, but rather assignable almost solely to seed plants. We show that early diverging land plants and presumably streptophyte algae share a co-localization of all rRNA genes within one repeat unit. This raises the possibility that the state of rDNA gene co-localization had occurred in their common ancestor. Separate rDNA arrays were identified for all basal seed plants and water ferns, implying at least two independent 5S rDNA transposition events during land plant evolution. Screening for 5S derived Cassandra transposable elements which might have played a role during the transposition events, indicated that this retrotransposon is absent in early diverging vascular plants including early fern lineages. Thus, Cassandra can be rejected as a primary mechanism for 5S rDNA transposition in water ferns. However, the evolution of Cassandra and other eukaryotic 5S derived elements might have been a side effect of the 5S rDNA cluster formation. Structural analysis of the intergenic spacers of the ribosomal clusters revealed that transposition events partially affect spacer regions and suggests a slightly different transcription regulation of 5S rDNA in early land plants. 5S rDNA upstream regulatory elements are highly divergent or absent from the LSU-5S spacers of most early divergent land plant lineages. Several putative scenarios and mechanisms involved in the concerted relocation of hundreds of 5S rRNA gene copies are discussed.

What does it take to resolve relationships and to identify species with molecular markers? An example from the epiphytic Rhipsalideae (Cactaceae).

PREMISE OF THE STUDY: The Cactaceae are a major New World plant family and popular in horticulture. Still, taxonomic units and species limits have been difficult to define, and molecular phylogenetic studies so far have yielded largely unresolved trees, so relationships within Cactaceae remain insufficiently understood. This study focuses on the predominantly epiphytic tribe Rhipsalideae and evaluates the utility of a spectrum of plastid genomic regions. • METHODS: We present a phylogenetic study including 52 of the 53 Rhipsalideae species and all the infraspecific taxa. Seven regions (trnK intron, matK, rbcL, rps3-rpl16, rpl16 intron, psbA-trnH, trnQ-rps16), ca. 5600 nucleotides (nt) were sequenced per sample. The regions used were evaluated for their phylogenetic performance and performance in DNA-based species recognition based on operational taxonomic units (OTUs) defined beforehand. • KEY RESULTS: The Rhipsalideae are monophyletic and contain five clades that correspond to the genera Rhipsalis, Lepismium, Schlumbergera, Hatiora, and Rhipsalidopsis. The species-level tree was well resolved and supported; the rpl16 and trnK introns yielded the best phylogenetic signal. Although the psbA-trnH and trnQ-rps16 spacers were the most successful individual regions for OTU identification, their success rate did not significantly exceed 70%. The highest OTU identification rate of 97% was found using the combination of psbA-trnH, rps3-rpl16, trnK intron, and trnQ-rps16 as a minimum possible marker length (ca. 1660 nt). • CONCLUSIONS: The phylogenetic performance of a marker is not determined by the level of sequence variability, and species discrimination power does not necessarily correlate with phylogenetic utility.