Intra-leaf modeling of Cannabis leaflet shape produces leaf models that predict genetic and developmental identities.

The iconic, palmately compound leaves of Cannabis have attracted significant attention in the past. However, investigations into the genetic basis of leaf shape or its connections to phytochemical composition have yielded inconclusive results. This is partly due to prominent changes in leaflet number within a single plant during development, which has so far prevented the proper use of common morphometric techniques. Here, we present a new method that overcomes the challenge of nonhomologous landmarks in palmate, pinnate, and lobed leaves, using Cannabis as an example. We model corresponding pseudo-landmarks for each leaflet as angle-radius coordinates and model them as a function of leaflet to create continuous polynomial models, bypassing the problems associated with variable number of leaflets between leaves. We analyze 341 leaves from 24 individuals from nine Cannabis accessions. Using 3591 pseudo-landmarks in modeled leaves, we accurately predict accession identity, leaflet number, and relative node number. Intra-leaf modeling offers a rapid, cost-effective means of identifying Cannabis accessions, making it a valuable tool for future taxonomic studies, cultivar recognition, and possibly chemical content analysis and sex identification, in addition to permitting the morphometric analysis of leaves in any species with variable numbers of leaflets or lobes.

The Dynamic Interplay Between Ribosomal DNA and Transposable Elements: A Perspective From Genomics and Cytogenetics.

Although both are salient features of genomes, at first glance ribosomal DNAs and transposable elements are genetic elements with not much in common: whereas ribosomal DNAs are mainly viewed as housekeeping genes that uphold all prime genome functions, transposable elements are generally portrayed as selfish and disruptive. These opposing characteristics are also mirrored in other attributes: organization in tandem (ribosomal DNAs) versus organization in a dispersed manner (transposable elements); evolution in a concerted manner (ribosomal DNAs) versus evolution by diversification (transposable elements); and activity that prolongs genomic stability (ribosomal DNAs) versus activity that shortens it (transposable elements). Re-visiting relevant instances in which ribosomal DNA-transposable element interactions have been reported, we note that both repeat types share at least four structural and functional hallmarks: (1) they are repetitive DNAs that shape genomes in evolutionary timescales, (2) they exchange structural motifs and can enter co-evolution processes, (3) they are tightly controlled genomic stress sensors playing key roles in senescence/aging, and (4) they share common epigenetic marks such as DNA methylation and histone modification. Here, we give an overview of the structural, functional, and evolutionary characteristics of both ribosomal DNAs and transposable elements, discuss their roles and interactions, and highlight trends and future directions as we move forward in understanding ribosomal DNA-transposable element associations.

Parallel anagenetic patterns in endemic Artemisia species from three Macaronesian archipelagos.

Anagenetic speciation is an important mode of evolution in oceanic islands, yet relatively understudied compared to adaptive radiation. In the Macaronesian region, three closely related species of Artemisia (i.e. A. argentea, A. thuscula and A. gorgonum) are each endemic from a single archipelago (i.e. Madeira, Canary Islands and Cape Verde, respectively), representing a perfect opportunity to study three similar but independent anagenetic speciation processes. By analysing plastid and nuclear DNA sequences, as well as nuclear DNA amount data, generated from a comprehensive sampling in all the islands and archipelagos where these species are currently distributed, we intend to find common evolutionary patterns that help us explain the limited taxonomic diversification experienced by endemic Macaronesian Artemisia. Our time-calibrated phylogenetic reconstruction suggested that divergence among the three lineages occurred in a coincidental short period of time during the Pleistocene. Haplotype and genetic differentiation analyses showed similar diversity values among A. argentea, A. thuscula and A. gorgonum. Clear phylogeographic patterns-showing comparable genetic structuring among groups of islands-were also found within the three archipelagos. Even from the cytogenetic point of view, the three species presented similarly lower genome size values compared to the mainland closely related species A. arborescens. We hypothesize that the limited speciation experienced by the endemic Artemisia in Madeira, Canary Islands and Cape Verde archipelagos could be related to their recent parallel evolutionary histories as independent lineages, combined with certain shared characteristics of seed dispersal, pollen transport and type of habitat.

Phylogenomics and morphological evolution of the mega-diverse genus Artemisia (Asteraceae: Anthemideae): implications for its circumscription and infrageneric taxonomy.

BACKGROUND AND AIMS: Artemisia is a mega-diverse genus consisting of ~400 species. Despite its medicinal importance and ecological significance, a well-resolved phylogeny for global Artemisia, a natural generic delimitation and infrageneric taxonomy remain missing, owing to the obstructions from limited taxon sampling and insufficient information on DNA markers. Its morphological characters, such as capitulum, life form and leaf, show marked variations and are widely used in its infrageneric taxonomy. However, their evolution within Artemisia is poorly understood. Here, we aimed to reconstruct a well-resolved phylogeny for global Artemisia via a phylogenomic approach, to infer the evolutionary patterns of its key morphological characters and to update its circumscription and infrageneric taxonomy. METHODS: We sampled 228 species (258 samples) of Artemisia and its allies from both fresh and herbarium collections, covering all the subgenera and its main geographical areas, and conducted a phylogenomic analysis based on nuclear single nucleotide polymorphisms (SNPs) obtained from genome skimming data. Based on the phylogenetic framework, we inferred the possible evolutionary patterns of six key morphological characters widely used in its previous taxonomy. KEY RESULTS: The genus Kaschgaria was revealed to be nested in Artemisia with strong support. A well-resolved phylogeny of Artemisia consisting of eight highly supported clades was recovered, two of which were identified for the first time. Most of the previously recognized subgenera were not supported as monophyletic. Evolutionary inferences based on the six morphological characters showed that different states of these characters originated independently more than once. CONCLUSIONS: The circumscription of Artemisia is enlarged to include the genus Kaschgaria. The morphological characters traditionally used for the infrageneric taxonomy of Artemisia do not match the new phylogenetic tree. They experienced a more complex evolutionary history than previously thought. We propose a revised infrageneric taxonomy of the newly circumscribed Artemisia, with eight recognized subgenera to accommodate the new results.

Novel Insights into the Nature of Intraspecific Genome Size Diversity in Cannabis sativa L.

Cannabis sativa has been used for millennia in traditional medicine for ritual purposes and for the production of food and fibres, thus, providing important and versatile services to humans. The species, which currently has a worldwide distribution, strikes out for displaying a huge morphological and chemical diversity. Differences in Cannabis genome size have also been found, suggesting it could be a useful character to differentiate between accessions. We used flow cytometry to investigate the extent of genome size diversity across 483 individuals belonging to 84 accessions, with a wide range of wild/feral, landrace, and cultivated accessions. We also carried out sex determination using the MADC2 marker and investigated the potential of flow cytometry as a method for early sex determination. All individuals were diploid, with genome sizes ranging from 1.810 up to 2.152 pg/2C (1.189-fold variation), apart from a triploid, with 2.884 pg/2C. Our results suggest that the geographical expansion of Cannabis and its domestication had little impact on its overall genome size. We found significant differences between the genome size of male and female individuals. Unfortunately, differences were, however, too small to be discriminated using flow cytometry through the direct processing of combined male and female individuals.

The Use of Cannabis sativa L. for Pest Control: From the Ethnobotanical Knowledge to a Systematic Review of Experimental Studies.

Background: Despite the benefits that synthetic pesticides have provided in terms of pest and disease control, they cause serious long-term consequences for both the environment and living organisms. Interest in eco-friendly products has subsequently increased in recent years. Methods: This article briefly analyzes the available ethnobotanical evidence regarding the use of Cannabis sativa as a pesticide and offers a systematic review of experimental studies. Results: Our findings indicate that both ethnobotanical and experimental procedures support the use of C. sativa as a pesticide, as remarkable toxicity has been observed against pest organisms. The results included in the systematic review of experimental studies (n=30) show a high degree of heterogeneity, but certain conclusions can be extracted to guide further research. For instance, promising pesticide properties were reported for most of the groups of species tested, especially Arachnida and Insecta; the efficacy of C. sativa as a pesticide can be derived from a wide variety of compounds that it contains and possible synergistic effects; it is crucial to standardize the phytochemical profile of C. sativa plants used as well as to obtain easily reproducible results; appropriate extraction methods should be explored; and upper inflorescences of the plant may be preferred for the production of the essential oil, but further studies should explore better other parts of the plant. Conclusion: In the coming years, as new findings are produced, the promising potential of C. sativa as a pesticide will be elucidated, and reviews such as the present one constitute useful basic tools to make these processes easier.

Plastome Diversity and Phylogenomic Relationships in Asteraceae.

Plastid genomes are in general highly conserved given their slow evolutionary rate, and thus large changes in their structure are unusual. However, when specific rearrangements are present, they are often phylogenetically informative. Asteraceae is a highly diverse family whose evolution is long driven by polyploidy (up to 48x) and hybridization, both processes usually complicating systematic inferences. In this study, we generated one of the most comprehensive plastome-based phylogenies of family Asteraceae, providing information about the structure, genetic diversity and repeat composition of these sequences. By comparing the whole-plastome sequences obtained, we confirmed the double inversion located in the long single-copy region, for most of the species analyzed (with the exception of basal tribes), a well-known feature for Asteraceae plastomes. We also showed that genome size, gene order and gene content are highly conserved along the family. However, species representative of the basal subfamily Barnadesioideae-as well as in the sister family Calyceraceae-lack the pseudogene rps19 located in one inverted repeat. The phylogenomic analysis conducted here, based on 63 protein-coding genes, 30 transfer RNA genes and 21 ribosomal RNA genes from 36 species of Asteraceae, were overall consistent with the general consensus for the family's phylogeny while resolving the position of tribe Senecioneae and revealing some incongruences at tribe level between reconstructions based on nuclear and plastid DNA data.

Traditional uses of Cannabis: An analysis of the CANNUSE database.

ETHNOPHARMACOLOGICAL RELEVANCE: Cannabis is one of the most versatile genera in terms of plant use and has been exploited by humans for millennia. Nowadays, Cannabis is the centre of many scientific studies, most of them focusing on chemical composition and medicinal values. While new and varied applications are continuously being developed, the knowledge surrounding less common uses of the plant is slowly disappearing. AIM OF THE REVIEW: We have analysed diversity of global data of Cannabis traditional uses, to investigate if certain plant parts are significantly associated with particular Cannabis use. We wanted to uncover potential associations between the plant parts used for the treatment of different body systems and ailments. MATERIALS AND METHODS: We have analysed the extensive database of Cannabis traditional uses (CANNUSE). This database contains 2330 data entries of Cannabis ethnobotanical uses from over 40 countries across the world. The dataset was divided into five general groups based on the type of use: medicinal, alimentary, psychoactive, fibre and other uses. Given the abundance of human medicinal uses, detailed analysis was done on the subset of 1167 data entries. We analysed the relationship between 16 body system categories and ailments treated with Cannabis plant parts. We used a Pearson's chi-square and Fisher's exact test, to determine which Cannabis parts are characteristic of treatment for specific ailments. RESULTS: In this dataset, the majority of reports were represented by medicinal (75.41%), followed by psychoactive (8.35%) and alimentary (7.29%) use. The most commonly used plant parts were leaf (50.51%), seed (15.38%) and inflorescence (11.35%). We found that different Cannabis plant parts were significantly associated with different uses; the leaf was typically used for medicinal, seed for alimentary and inflorescence for psychoactive use. Regarding the human medicinal uses, most common were reports for treatments of the digestive system and nutritional disorders (17.66%), nervous system and mental disorders (16.24%), followed by pain and inflammations (12.21%). We found a significant relationship between the use of certain Cannabis parts and treatment of ailments and body systems categories; leaf was significantly associated with treatment of two categories: skin and subcutaneous tissue disorders and circulatory system and blood disorders; seed use was associated with musculoskeletal system disorders and traumas; while inflorescence use shows a statistical support for treatment of nervous system and mental disorders. CONCLUSION: Several pharmaceutical companies are intensely working on developing new drugs with isolated chemical compounds or crude extracts, almost exclusively from Cannabis inflorescences. However, our review revealed that use of leaf or seed in traditional medicine is often more important than use of inflorescence for the treatment of certain ailments. A review of traditional medicine provides a body of knowledge and an initial pathway to identify landraces and plant parts that could have an important role in future medicinal research. We are confident that traditional medicine still has a large potential for modern medicine. As more information on Cannabis diversity (genetics, biochemistry, and clinical studies) becomes available, ethnobotanical data are poised to be of much greater significance.

CANNUSE, a database of traditional Cannabis uses-an opportunity for new research.

Cannabis is one of the most versatile genera in terms of plant uses and has been exploited by humans for millennia due to its medicinal properties, strong fibres, nutritious seeds and psychoactive resin. Nowadays, Cannabis is the centre of many scientific studies, which mainly focus on its chemical composition and medicinal properties. Unfortunately, while new applications of this plant are continuously being developed, some of its traditional uses are becoming rare and even disappearing altogether. Information on traditional uses of Cannabis is vast, but it is scattered across many publication sources in different formats, so synthesis and standardization of these data are increasingly important. The CANNUSE database provides an organized information source for scientists and general public interested in different aspects of Cannabis use. It contains over 2300 entries from 649 publications related to medicinal, alimentary, fibre and other uses from different geographical areas and cultures around the world. We believe this database will serve as a starting point for new research and development strategies based on the traditional knowledge. Database URL: http://cannusedb.csic.es.

Phenolic Compounds Content and Genetic Diversity at Population Level across the Natural Distribution Range of Bearberry (Arctostaphylos uva-ursi, Ericaceae) in the Iberian Peninsula.

Bearberry (Arctostaphylos uva-ursi) is a medicinal plant traditionally employed for the treatment of urinary tract infections due to high contents of arbutin (hydroquinone ß-D-glucoside), which is now mainly used as a natural skin-whitening agent in cosmetics. Bearberry has also been proposed as a natural antioxidant additive due to the high contents of phenolic compounds in leaves. We studied the variation on phenolic compounds in 42 wild populations of bearberry, aiming to elucidate if intrinsic biological, climatic, and/or geographic factors affect phenolic contents across its natural distribution in the Iberian Peninsula. Bearberry leaves were collected during autumn over a three-year period (2014-2016) in populations across a latitude and altitude gradient. Methanolic extracts showed a wide range of variation in total phenols content, and different phenolic profiles regarding arbutin (levels of this major constituent varied from 87 to 232 mg/g dr wt), but also catechin and myricetin contents, which were affected by geographic and climatic factors. Moderate levels of variation on genome size-assessed by flow cytometry-and on two plastid DNA regions were also detected among populations. Genetic and cytogenetic differentiation of populations was weakly but significantly associated to phytochemical diversity. Elite bearberry genotypes with higher antioxidant capacity were subsequently identified.

Human-like telomeres in Zostera marina reveal a mode of transition from the plant to the human telomeric sequences.

A previous study describing the genome of Zostera marina, the most widespread seagrass in the Northern hemisphere, revealed some genomic signatures of adaptation to the aquatic environment such as the loss of stomatal genes, while other functions such as an algal-like cell wall composition were acquired. Beyond these, the genome structure and organization were comparable with those of the majority of plant genomes sequenced, except for one striking feature that went unnoticed at that time: the presence of human-like instead of the expected plant-type telomeric sequences. By using different experimental approaches including fluorescence in situ hybridization (FISH), genome skimming by next-generation sequencing (NGS), and analysis of non-coding transcriptome, we have confirmed its telomeric location in the chromosomes of Z. marina. We have also identified its telomerase RNA (TR) subunit, confirming the presence of the human-type telomeric sequence in the template region. Remarkably, this region was found to be very variable even in clades with a highly conserved telomeric sequence across their species. Based on this observation, we propose that alternative annealing preferences in the template borders can explain the transition between the plant and human telomeric sequences. The further identification of paralogues of TR in several plant genomes led us to the hypothesis that plants may retain an increased ability to change their telomeric sequence. We discuss the implications of this occurrence in the evolution of telomeres while introducing a mechanistic model for the transition from the plant to the human telomeric sequences.

Reconstructing phylogenetic relationships based on repeat sequence similarities.

A recent phylogenetic method based on genome-wide abundance of different repeat types proved to be useful in reconstructing the evolutionary history of several plant and animal groups. Here, we demonstrate that an alternative information source from the repeatome can also be employed to infer phylogenetic relationships among taxa. Specifically, this novel approach makes use of the repeat sequence similarity matrices obtained from the comparative clustering analyses of RepeatExplorer 2, which are subsequently transformed to between-taxa distance matrices. These pairwise matrices are used to construct neighbour-joining trees for each of the top most-abundant clusters and they are finally summarized in a consensus network. This methodology was tested on three groups of angiosperms and one group of insects, resulting in congruent evolutionary hypotheses compared to more standard systematic analyses based on commonly used DNA markers. We propose that the combined application of these phylogenetic approaches based on repeat abundances and repeat sequence similarities could be helpful to understand mechanisms governing genome and repeatome evolution.

Global distribution patterns and niche modelling of the invasive Kalanchoe × houghtonii (Crassulaceae).

Invasive alien species are currently considered one of the main threats to global biodiversity. One of the most rapidly expanding invasive plants in recent times is Kalanchoe × houghtonii (Crassulaceae), an artificial hybrid created in the 1930s in the United States by experimental crossings between K. daigremontiana and K. tubiflora, two species endemic to Madagascar. Thanks to its large colonizing capacity (mainly derived from the production of asexual plantlets), K. × houghtonii soon escaped from cultivation and quickly spread in many parts of the world. However, its actual range is not well known due to the lack of a formal description until recent times (2006) and its strong morphological resemblance with one of its parentals (K. daigremontiana). The present study was aimed, in the first instance, to delimit the present distribution area of K. × houghtonii at the global scale by gathering and validating all its occurrences and to track its colonization history. Currently, K. × houghtonii can be found on all continents except Antarctica, although it did not reach a global distribution until the 2000s. Its potential distribution, estimated with MaxEnt modelling software, is mainly centered in subtropical regions, from 20° to 40° of both northern and southern latitudes, mostly in areas with a high anthropogenic activity. Unexpectedly, concomitant to a poleward migration, future niche models suggest a considerable reduction of its range by up to one-third compared to the present, which might be related with the Crassulaceaean Acid Metabolism (CAM) of K. × houghtonii. Further research may shed light as to whether a decrease in potential habitats constitutes a general pattern for Crassulaceae and CAM plants.

Genome size variation at constant chromosome number is not correlated with repetitive DNA dynamism in Anacyclus (Asteraceae).

BACKGROUND AND AIMS: Changes in the amount of repetitive DNA (dispersed and tandem repeats) are considered the main contributors to genome size variation across plant species in the absence of polyploidy. However, the study of repeatome dynamism in groups showing contrasting genomic features and complex evolutionary histories is needed to determine whether other processes underlying genome size variation may have been overlooked. The main aim here was to elucidate which mechanism best explains genome size evolution in Anacyclus (Asteraceae). METHODS: Using data from Illumina sequencing, we analysed the repetitive DNA in all species of Anacyclus, a genus with a reticulate evolutionary history, which displays significant genome size and karyotype diversity albeit presenting a stable chromosome number. KEY RESULTS: By reconstructing ancestral genome size values, we inferred independent episodes of genome size expansions and contractions during the evolution of the genus. However, analysis of the repeatome revealed a similar DNA repeat composition across species, both qualitative and quantitative. Using comparative methods to study repeatome dynamics in the genus, we found no evidence for repeat activity causing genome size variation among species. CONCLUSIONS: Our results, combined with previous cytogenetic data, suggest that genome size differences in Anacyclus are probably related to chromosome rearrangements involving losses or gains of chromosome fragments, possibly associated with homoploid hybridization. These could represent balanced rearrangements that do not disrupt gene dosage in merged genomes, for example via chromosome segment exchanges.

Progress in the study of genome size evolution in Asteraceae: analysis of the last update.

The Genome Size in Asteraceae Database (GSAD, http://www.asteraceaegenomesize.com) has been recently updated, with data from papers published or in press until July 2018. This constitutes the third release of GSAD, currently containing 4350 data entries for 1496 species, which represent a growth of 22.52% in the number of species with available genome size data compared with the previous release, and a growth of 57.72% in terms of entries. Approximately 6% of Asteraceae species are covered in terms of known genome sizes. The number of source papers included in this release (198) means a 48.87% increase with respect to release 2.0. The significant data increase was exploited to study the genome size evolution in the family from a phylogenetic perspective. Our results suggest that the role of chromosome number in genome size diversity within Asteraceae is basically associated to polyploidy, while dysploidy would only cause minor variation in the DNA amount along the family. Among diploid taxa, we found that the evolution of genome size shows a strong phylogenetic signal. However, this trait does not seem to evolve evenly across the phylogeny, but there could be significant scale and clade-dependent patterns. Our analyses indicate that the phylogenetic signal is stronger at low taxonomic levels, with certain tribes standing out as hotspots of autocorrelation between genome size and phylogeny. Finally, we also observe meaningful associations among nuclear DNA content on Asteraceae species and other phenotypical and ecological traits (i.e. plant habit and invasion ability). Overall, this study emphasizes the need to continue generating and analysing genome size data in order to puzzle out the evolution of this parameter and its many biological correlates.

Phylogeography of Dictyota fasciola and Dictyota mediterranea (Dictyotales, Phaeophyceae): unexpected patterns on the Atlantic-Mediterranean marine transition and taxonomic implications.

The Atlantic-Mediterranean marine transition is a fascinating biogeographic region, but still very poorly studied from the point of view of seaweed phylogeography. Dictyota fasciola and D. mediterranea (Dictyotales, Phaeophyceae) are two currently recognized sister species that share a large part of their distribution along the Mediterranean Sea and the Atlantic Ocean, representing a unique study model to understand the diversification processes experienced by macroalgae during and after Messinian at this marine region. In this study, we sampled 102 individuals of D. fasciola and D. mediterranea from 32 localities along their distribution range and sequenced the mitochondrial cox1 and the chloroplast rbcL-rbcS DNA regions for all the samples. Our data do not support the occurrence of two sister species but a morphologically variable and highly genetic diverse species or a complex of species. Most of the observed genetic diversity corresponds to the Mediterranean populations, whereas the Atlantic ones are much more homogeneous. The early-diverged lineages inferred from both mtDNA and cpDNA phylogenetic reconstructions were constituted by samples from the Mediterranean Sea. Together, these results suggest that the Mediterranean Sea acted as a refugium for the D. fasciola-D. mediterranea lineage during the geologic and climatic changes occurred on the region since the Miocene, subsequently dispersing to the Atlantic Ocean.

A phylogenetic road map to antimalarial Artemisia species.

ETHNOPHARMACOLOGICAL RELEVANCE: The discovery of the antimalarial agent artemisinin is considered one of the most significant success stories of ethnopharmacological research in recent times. The isolation of artemisinin was inspired by the use of Artemisia annua in traditional Chinese medicine (TCM) and was awarded a Nobel Prize in 2015. Antimalarial activity has since been demonstrated for a range of other Artemisia species, suggesting that the genus could provide alternative sources of antimalarial treatments. Given the stunning diversity of the genus (c. 500 species), a prioritisation of taxa to be investigated for their likely antimalarial properties is required. MATERIALS AND METHODS: Here we use a phylogenetic approach to explore the potential for identifying species more likely to possess antimalarial properties. Ethnobotanical data from literature reports is recorded for 117 species. Subsequent phylogenetically informed analysis was used to identify lineages in which there is an overrepresentation of species used to treat malarial symptoms, and which could therefore be high priority for further investigation of antimalarial activity. RESULTS: We show that these lineages indeed include several species with documented antimalarial activity. To further inform our approach, we use LC-MS/MS analysis to explore artemisinin content in fifteen species from both highlighted and not highlighted lineages. We detected artemisinin in nine species, in eight of them for the first time, doubling the number of Artemisia taxa known to content this molecule. CONCLUSIONS: Our findings indicate that artemisinin may be widespread across the genus, providing an accessible local resource outside the distribution area of Artemisia annua.

Opposite trends in the genus Monsonia (Geraniaceae): specialization in the African deserts and range expansions throughout eastern Africa.

The African Austro-temperate Flora stands out by its important species richness. A distinctive element of this flora is Monsonia (Geraniaceae), mostly found in the Namib-Karoo but also in the Natal-Drakensberg, the Somalian Zambezian and the Saharo-Arabian regions. Here, we reconstruct the evolution and biogeographic history of Monsonia based on nuclear and plastid markers, and examine the role of morphological and niche evolution in its diversification using species distribution modeling and macroevolutionary models. Our results indicate that Monsonia first diversified in the Early Miocene c.21 Ma, coinciding with the start of desertification in southwestern Africa. An important diversification occurred c. 4-6 Ma, after a general cooling trend in western South Africa and the rising of the Eastern African Mountains. The resulting two main lineages of Monsonia are constituted by: (1) Namib-Karoo succulents, and (2) herbs of the Natal-Drakensberg plus three species that further colonised steppes in north and eastern Africa. The highest diversity of Monsonia is found in the Namib-Karoo coastal belt, within a mosaic-like habitat structure. Diversification was likely driven by biome shifts and key innovations such as water-storing succulent stems and anemochorous fruits. In contrast, and unlike other arid-adapted taxa, all species of Monsonia share a C3 metabolism.

Key processes for Cheirolophus (Asteraceae) diversification on oceanic islands inferred from AFLP data.

The radiation of the genus Cheirolophus (Asteraceae) in Macaronesia constitutes a spectacular case of rapid diversification on oceanic islands. Twenty species - nine of them included in the IUCN Red List of Threatened Species - have been described to date inhabiting the Madeiran and Canarian archipelagos. A previous phylogenetic study revealed that the diversification of Cheirolophus in Macaronesia started less than 2 Ma. As a result of such an explosive speciation process, limited phylogenetic resolution was reported, mainly due to the low variability of the employed molecular markers. In the present study, we used highly polymorphic AFLP markers to i) evaluate species' boundaries, ii) infer their evolutionary relationships and iii) investigate the patterns of genetic diversity in relation to the potential processes likely involved in the radiation of Cheirolophus. One hundred and seventy-two individuals representing all Macaronesian Cheirolophus species were analysed using 249 AFLP loci. Our results suggest that geographic isolation played an important role in this radiation process. This was likely driven by the combination of poor gene flow capacity and a good ability for sporadic long-distance colonisations. In addition, we also found some traces of introgression and incipient ecological adaptation, which could have further enhanced the extraordinary diversification of Cheirolophus in Macaronesia. Last, we hypothesize that current threat categories assigned to Macaronesian Cheirolophus species do not reflect their respective evolutionary relevance, so future evaluations of their conservation status should take into account the results presented here.

The explosive radiation of Cheirolophus (Asteraceae, Cardueae) in Macaronesia.

BACKGROUND: Considered a biodiversity hotspot, the Canary Islands have been the key subjects of numerous evolutionary studies concerning a large variety of organisms. The genus Cheirolophus (Asteraceae) represents one of the largest plant radiations in the Canarian archipelago. In contrast, only a few species occur in the Mediterranean region, the putative ancestral area of the genus. Here, our main aim was to reconstruct the phylogenetic and biogeographic history of Cheirolophus with special focus on explaining the origin of the large Canarian radiation. RESULTS: We found significant incongruence in phylogenetic relationships between nuclear and plastid markers. Each dataset provided resolution at different levels in Cheirolophus: the nuclear markers resolved the backbone of the phylogeny while the plastid data provided better resolution within the Canarian clade. The origin of Cheirolophus was dated in the Mid-Late Miocene, followed by rapid diversification into the three main Mediterranean lineages and the Macaronesian clade. A decrease in diversification rates was inferred at the end of the Miocene, with a new increase in the Late Pliocene concurrent with the onset of the Mediterranean climate. Diversification within the Macaronesian clade started in the Early-Mid Pleistocene, with unusually high speciation rates giving rise to the extant insular diversity. CONCLUSIONS: Climate-driven diversification likely explains the early evolutionary history of Cheirolophus in the Mediterranean region. It appears that the exceptionally high diversification rate in the Canarian clade was mainly driven by allopatric speciation (including intra- and interisland diversification). Several intrinsic (e.g. breeding system, polyploid origin, seed dispersal syndrome) and extrinsic (e.g. fragmented landscape, isolated habitats, climatic and geological changes) factors probably contributed to the progressive differentiation of populations resulting in numerous microendemisms. Finally, hybridization events and emerging ecological adaptation may have also reinforced the diversification process.