Chloroplast Genome Provides Insights into Molecular Evolution and Species Relationship of Fleabanes (Erigeron: Tribe Astereae, Asteraceae) in the Juan Fernández Islands, Chile.

Erigeron represents the third largest genus on the Juan Fernández Islands, with six endemic species, five of which occur exclusively on the younger Alejandro Selkirk Island with one species on both islands. While its continental sister species is unknown, Erigeron on the Juan Fernández Islands appears to be monophyletic and most likely evolved from South American progenitor species. We characterized the complete chloroplast genomes of five Erigeron species, including accessions of E. fernandezia and one each from Alejandro Selkirk and Robinson Crusoe Islands, with the purposes of elucidating molecular evolution and phylogenetic relationships. We found highly conserved chloroplast genomes in size, gene order and contents, and further identified several mutation hotspot regions. In addition, we found two positively selected chloroplast genes (ccsA and ndhF) among species in the islands. The complete plastome sequences confirmed the monophyly of Erigeron in the islands and corroborated previous phylogenetic relationships among species. New findings in the current study include (1) two major lineages, E. turricola-E. luteoviridis and E. fernandezia-E. ingae-E. rupicola, (2) the non-monophyly of E. fernandezia occurring on the two islands, and (3) the non-monophyly of the alpine species E. ingae complex.

Human Impacts on the Vegetation of the Juan Fernández (Robinson Crusoe) Archipelago.

The human footprint on marine and terrestrial ecosystems of the planet has been substantial, largely due to the increase in the human population with associated activities and resource utilization. Oceanic islands have been particularly susceptible to such pressures, resulting in high levels of loss of biodiversity and reductions in the numbers and sizes of wild populations. One archipelago that has suffered from human impact has been the Juan Fernández (Robinson Crusoe) Archipelago, a Chilean national park located 667 km west of Valparaíso at 33° S. latitude. The park consists of three principal islands: Robinson Crusoe Island (48 km2); Santa Clara Island (2.2 km2); and Alejandro Selkirk Island (50 km2). The latter island lies 181 kms further west into the Pacific Ocean. No indigenous peoples ever visited or lived on any of these islands; they were first discovered by the Spanish navigator, Juan Fernández, in 1574. From that point onward, a series of European visitors arrived, especially to Robinson Crusoe Island. They began to cut the forests, and such activity increased with the establishment of a permanent colony in 1750 that has persisted to the present day. Pressures on the native and endemic flora increased due to the introduction of animals, such as goats, rats, dogs, cats, pigs, and rabbits. Numerous invasive plants also arrived, some deliberately introduced and others arriving inadvertently. At present, more than three-quarters of the endemic and native vascular species of the flora are either threatened or endangered. The loss of vegetation has also resulted in a loss of genetic variability in some species as populations are reduced in size or go extinct. It is critical that the remaining genetic diversity be conserved, and genomic markers would provide guidelines for the conservation of the diversity of the endemic flora. To preserve the unique flora of these islands, further conservation measures are needed, especially in education and phytosanitary monitoring.

Assessing signals of selection and historical demography to develop conservation strategies in the Chilean emblematic Araucaria araucana.

Loss of genetic diversity reduces the ability of species to evolve and respond to environmental change. Araucaria araucana is an emblematic conifer species from southern South America, with important ethnic value for the Mapuche people (Pehuenche); the Chilean Government has catalogued its conservation status as vulnerable. Climatic fluctuations were potentially a major impact in the genetic variation within many tree species. In this context, the restricted geographic distribution of A. araucana in Chile appears to be a consequence of the Last Glacial Maximum (LGM). During the past two centuries, strong human intervention has also affected the geographical distribution and population sizes of A. araucana. Reduction of population size may cause loss of genetic diversity, which could affect frequency of adaptive loci. The aims of this study were to know the existence of potential loci under selection and populations with genetic, demographic disequilibrium in the Chilean distribution of A. araucana. Based on 268 polymorphic AFLP loci, we have investigated potential loci under selection and genetic, demographic disequilibrium within seven Chilean populations of Araucaria araucana. Correlation of 41 outlier loci with the environmental variables of precipitation and temperature reveals signatures of selection, whereas 227 neutral loci provide estimates of demographic equilibrium and genetic population structure. Three populations are recommended as priorities for conservation.

Plastid Phylogenomics of Dendroseris (Cichorieae; Asteraceae): Insights Into Structural Organization and Molecular Evolution of an Endemic Lineage From the Juan Fernández Islands.

Dendroseris D. Don comprises 11 species endemic to the Juan Fernández islands in Chile. They demonstrate spectacular and unusual growth forms of rosette trees with extremely variable morphology and occupy wide ecological ranges on the islands. These unique plants are now highly threatened with extinction with very small population sizes, typically consisting of 10 or fewer individuals in wild. Despite morphological and ecological divergence among species of Dendroseris, their monophyly has been supported in previous studies, but with little resolution among subgeneric groups. We assembled seven complete plastome sequences from seven species of Dendroseris, including representatives from three subgenera, and carried out comparative phylogenomic analyses. The plastomes are highly conserved in gene content and order, with size ranging from 152,199 to 152,619 bp and containing 130 genes (87 coding genes, 6 rRNA genes, and 37 tRNA genes). Plastid phylogenomic analyses based on both the complete plastome sequences and 81 concatenated coding genes only show Dendroseris nested within Sonchus sensu lato, and also that inter-subgeneric relationships are fully resolved. Subg. Phoenicoseris is resolved as sister to the remaining species of the genus and a sister relationship between the two subgenera Dendroseris and Rea. Ten mutation hotspots from LSC and SSC regions and variable SSRs are identified as potential chloroplast markers for future phylogenetic and phylogeographic studies of Sonchus and related groups.

Differential Genome Size and Repetitive DNA Evolution in Diploid Species of Melampodium sect. Melampodium (Asteraceae).

Plant genomes vary greatly in composition and size mainly due to the diversity of repetitive DNAs and the inherent propensity for their amplification and removal from the host genome. Most studies addressing repeatome dynamics focus on model organisms, whereas few provide comprehensive investigations across the genomes of related taxa. Herein, we analyze the evolution of repeats of the 13 species in Melampodium sect. Melampodium, representing all but two of its diploid taxa, in a phylogenetic context. The investigated genomes range in size from 0.49 to 2.27 pg/1C (ca. 4.5-fold variation), despite having the same base chromosome number (x = 10) and very strong phylogenetic affinities. Phylogenetic analysis performed in BEAST and ancestral genome size reconstruction revealed mixed patterns of genome size increases and decreases across the group. High-throughput genome skimming and the RepeatExplorer pipeline were utilized to determine the repeat families responsible for the differences in observed genome sizes. Patterns of repeat evolution were found to be highly correlated with phylogenetic position, namely taxonomic series circumscription. Major differences found were in the abundances of the SIRE (Ty1-copia), Athila (Ty3-gypsy), and CACTA (DNA transposon) lineages. Additionally, several satellite DNA families were found to be highly group-specific, although their overall contribution to genome size variation was relatively small. Evolutionary changes in repetitive DNA composition and genome size were complex, with independent patterns of genome up- and downsizing throughout the evolution of the analyzed diploids. A model-based analysis of genome size and repetitive DNA composition revealed evidence for strong phylogenetic signal and differential evolutionary rates of major lineages of repeats in the diploid genomes.

Correction to: Factors driving adaptive radiation in plants of oceanic islands: a case study from the Juan Fernández Archipelago.

The article Factors driving adaptive radiation in plants of oceanic islands: a case study from the Juan Fernández Archipelago, written by Koji Takayama, Daniel J. Crawford, Patricio López­Sepúlveda, Josef Greimler, Tod F. Stuessy was originally published electronically on the publisher's internet portal (currently SpringerLink) on 13 March 2018 without open access.

Ragweeds and relatives: Molecular phylogenetics of Ambrosiinae (Asteraceae).

Ambrosiinae are one of the most distinct subtribes in the Heliantheae alliance (Asteraceae), mainly due to specialization toward wind pollination. Taxa of the subtribe are principally native to the Americas, although some species have attained a cosmopolitan distribution. Members of subtribe Engelmanniinae are considered close to Ambrosiinae, due to shared morphological traits. However, the placement of Ambrosiinae within the Heliantheae alliance has not yet been corroborated by phylogenetic analyses. In the present study, we test the circumscription of subtribe Ambrosiinae and examine relationships among its genera. We used sequence information from three plastid (psbA-trnH, trnQ-rps16 and trnL-F) and two nuclear (ITS and D35) marker regions. Phylogenetic inference analyses were conducted, applying Bayesian Inference (BI) and Maximum Likelihood (ML). Subtribe Ambrosiinae is found monophyletic or nearly so in all analyses. The genera Dugesia and Rojasianthe (previously considered part of subtribe Engelmanniinae) in some cases cluster together with Ambrosiinae; these genera are clearly not part of Engelmanniinae. Within Ambrosiinae, the genera Parthenium and Parthenice occupy basal positions, whereas members of the genus Ambrosia are the most derived representatives of the subtribe. Previous subdivision of Ambrosiinae into "Iveae" (members having androgynous capitula and free achenes) and "Ambrosieae" (genera with unisexual heads and achenes enclosed in burs) is not corroborated. Results also allow consideration of relationships among species and subgeneric groups within Parthenium, Iva, and Ambrosia.

Dating the Species Network: Allopolyploidy and Repetitive DNA Evolution in American Daisies (Melampodium sect. Melampodium, Asteraceae).

Allopolyploidy has played an important role in the evolution of the flowering plants. Genome mergers are often accompanied by significant and rapid alterations of genome size and structure via chromosomal rearrangements and altered dynamics of tandem and dispersed repetitive DNA families. Recent developments in sequencing technologies and bioinformatic methods allow for a comprehensive investigation of the repetitive component of plant genomes. Interpretation of evolutionary dynamics following allopolyploidization requires both the knowledge of parentage and the age of origin of an allopolyploid. Whereas parentage is typically inferred from cytogenetic and phylogenetic data, age inference is hampered by the reticulate nature of the phylogenetic relationships. Treating subgenomes of allopolyploids as if they belonged to different species (i.e., no recombination among subgenomes) and applying cross-bracing (i.e., putting a constraint on the age difference of nodes pertaining to the same event), we can infer the age of allopolyploids within the framework of the multispecies coalescent within BEAST2. Together with a comprehensive characterization of the repetitive DNA fraction using the RepeatExplorer pipeline, we apply the dating approach in a group of closely related allopolyploids and their progenitor species in the plant genus Melampodium (Asteraceae). We dated the origin of both the allotetraploid, Melampodium strigosum, and its two allohexaploid derivatives, Melampodium pringlei and Melampodium sericeum, which share both parentage and the direction of the cross, to the Pleistocene ($<$1.4 Ma). Thus, Pleistocene climatic fluctuations may have triggered formation of allopolyploids possibly in short intervals, contributing to difficulties in inferring the precise temporal order of allopolyploid species divergence of M. sericeum and M. pringlei. The relatively recent origin of the allopolyploids likely played a role in the near-absence of major changes in the repetitive fraction of the polyploids' genomes. The repetitive elements most affected by the postpolyploidization changes represented retrotransposons of the Ty1-copia lineage Maximus and, to a lesser extent, also Athila elements of Ty3-gypsy family.

Factors driving adaptive radiation in plants of oceanic islands: a case study from the Juan Fernández Archipelago.

Adaptive radiation is a common evolutionary phenomenon in oceanic islands. From one successful immigrant population, dispersal into different island environments and directional selection can rapidly yield a series of morphologically distinct species, each adapted to its own particular environment. Not all island immigrants, however, follow this evolutionary pathway. Others successfully arrive and establish viable populations, but they remain in the same ecological zone and only slowly diverge over millions of years. This transformational speciation, or anagenesis, is also common in oceanic archipelagos. The critical question is why do some groups radiate adaptively and others not? The Juan Fernández Islands contain 105 endemic taxa of angiosperms, 49% of which have originated by adaptive radiation (cladogenesis) and 51% by anagenesis, hence providing an opportunity to examine characteristics of taxa that have undergone both types of speciation in the same general island environment. Life form, dispersal mode, and total number of species in progenitors (genera) of endemic angiosperms in the archipelago were investigated from literature sources and compared with modes of speciation (cladogenesis vs. anagenesis). It is suggested that immigrants tending to undergo adaptive radiation are herbaceous perennial herbs, with leaky self-incompatible breeding systems, good intra-island dispersal capabilities, and flexible structural and physiological systems. Perhaps more importantly, the progenitors of adaptively radiated groups in islands are those that have already been successful in adaptations to different environments in source areas, and which have also undergone eco-geographic speciation. Evolutionary success via adaptive radiation in oceanic islands, therefore, is less a novel feature of island lineages but rather a continuation of tendency for successful adaptive speciation in lineages of continental source regions.

The Impact of Reconstruction Methods, Phylogenetic Uncertainty and Branch Lengths on Inference of Chromosome Number Evolution in American Daisies (Melampodium, Asteraceae).

Chromosome number change (polyploidy and dysploidy) plays an important role in plant diversification and speciation. Investigating chromosome number evolution commonly entails ancestral state reconstruction performed within a phylogenetic framework, which is, however, prone to uncertainty, whose effects on evolutionary inferences are insufficiently understood. Using the chromosomally diverse plant genus Melampodium (Asteraceae) as model group, we assess the impact of reconstruction method (maximum parsimony, maximum likelihood, Bayesian methods), branch length model (phylograms versus chronograms) and phylogenetic uncertainty (topological and branch length uncertainty) on the inference of chromosome number evolution. We also address the suitability of the maximum clade credibility (MCC) tree as single representative topology for chromosome number reconstruction. Each of the listed factors causes considerable incongruence among chromosome number reconstructions. Discrepancies between inferences on the MCC tree from those made by integrating over a set of trees are moderate for ancestral chromosome numbers, but severe for the difference of chromosome gains and losses, a measure of the directionality of dysploidy. Therefore, reliance on single trees, such as the MCC tree, is strongly discouraged and model averaging, taking both phylogenetic and model uncertainty into account, is recommended. For studying chromosome number evolution, dedicated models implemented in the program ChromEvol and ordered maximum parsimony may be most appropriate. Chromosome number evolution in Melampodium follows a pattern of bidirectional dysploidy (starting from x = 11 to x = 9 and x = 14, respectively) with no prevailing direction.

Genetic consequences of cladogenetic vs. anagenetic speciation in endemic plants of oceanic islands.

Adaptive radiation is a common mode of speciation among plants endemic to oceanic islands. This pattern is one of cladogenesis, or splitting of the founder population, into diverse lineages in divergent habitats. In contrast, endemic species have also evolved primarily by simple transformations from progenitors in source regions. This is anagenesis, whereby the founding population changes genetically and morphologically over time primarily through mutation and recombination. Gene flow among populations is maintained in a homogeneous environment with no splitting events. Genetic consequences of these modes of speciation have been examined in the Juan Fernández Archipelago, which contains two principal islands of differing geological ages. This article summarizes population genetic results (nearly 4000 analyses) from examination of 15 endemic species, involving 1716 and 1870 individuals in 162 and 163 populations (with amplified fragment length polymorphisms and simple sequence repeats, respectively) in the following genera: Drimys (Winteraceae), Myrceugenia (Myrtaceae), Rhaphithamnus (Verbenaceae), Robinsonia (Asteraceae, Senecioneae) and Erigeron (Asteraceae, Astereae). The results indicate that species originating anagenetically show high levels of genetic variation within the island population and no geographic genetic partitioning. This contrasts with cladogenetic species that show less genetic diversity within and among populations. Species that have been derived anagenetically on the younger island (1-2 Ma) contain less genetic variation than those that have anagenetically speciated on the older island (4 Ma). Genetic distinctness among cladogenetically derived species on the older island is greater than among similarly derived species on the younger island. An important point is that the total genetic variation within each genus analysed is comparable, regardless of whether adaptive divergence occurs.

Progressive migration and anagenesis in Drimys confertifolia of the Juan Fernández Archipelago, Chile.

A common mode of speciation in oceanic islands is by anagenesis, wherein an immigrant arrives and through time transforms by mutation, recombination, and drift into a morphologically and genetically distinct species, with the new species accumulating a high level of genetic diversity. We investigate speciation in Drimys confertifolia, endemic to the two major islands of the Juan Fernández Archipelago, Chile, to determine genetic consequences of anagenesis, to examine relationships among populations of D. confertifolia and the continental species D. winteri and D. andina, and to test probable migration routes between the major islands. Population genetic analyses were conducted using AFLPs and nuclear microsatellites of 421 individuals from 42 populations from the Juan Fernández islands and the continent. Drimys confertifolia shows a wide genetic variation within populations on both islands, and values of genetic diversity within populations are similar to those found within populations of the continental progenitor. The genetic results are compatible with the hypothesis of high levels of genetic variation accumulating within anagenetically derived species in oceanic islands, and with the concept of little or no geographical partitioning of this variation over the landscape. Analysis of the probability of migration within the archipelago confirms colonization from the older island, Robinson Crusoe, to the younger island Alejandro Selkirk.

Relationships and genetic consequences of contrasting modes of speciation among endemic species of Robinsonia (Asteraceae, Senecioneae) of the Juan Fernández Archipelago, Chile, based on AFLPs and SSRs.

This study analyses and compares the genetic signatures of anagenetic and cladogenetic speciation in six species of the genus Robinsonia (Asteraceae, Senecioneae), endemic to the Juan Fernández Islands, Chile. Population genetic structure was analyzed by amplified fragment length polymorphism (AFLP) and microsatellite (simple sequence repeat, SSR) markers from 286 and 320 individuals, respectively, in 28 populations. Each species is genetically distinct. Previous hypotheses of classification among these species into subgenera and sections, via morphological, phytochemical, isozymic and internal transcribed spacer (ITS) data, have been confirmed, except that R. saxatilis appears to be related to R. gayana rather than R. evenia. Analysis of phylogenetic results and biogeographic context suggests that five of these species have originated by cladogenesis and adaptive radiation on the older Robinson Crusoe Island. The sixth species, R. masafuerae, restricted to the younger Alejandro Selkirk Island, is closely related to and an anagenetic derivative of R. evenia from Robinson Crusoe. Microsatellite and AFLP data reveal considerable genetic variation among the cladogenetically derived species of Robinsonia, but within each the genetic variation is lower, highlighting presumptive genetic isolation and rapid radiation. The anagenetically derived R. masafuerae harbors a level of genetic variation similar to that of its progenitor, R. evenia. This is the first direct comparison of the genetic consequences of anagenetic and cladogenetic speciation in plants of an oceanic archipelago.

The importance of comprehensive phylogenetic (evolutionary) classification-a response to Schmidt-Lebuhn's commentary on paraphyletic taxa.

The review of paraphyly in botanical systematics by Schmidt-Lebuhn brings together a number of useful perspectives for the reader. It fails to offer new ideas, however, and it does not recognize the fallacies of strict cladistic classification, namely accepting only holophyletic groups, and insisting that sister groups have the same rank. The reason for adherence to these rules is to maintain the convenience of cladistic classification. While convenience in biological classification by itself is not necessarily bad, it becomes unacceptable when its use overshadows achieving a higher level of evolutionary (and phylogenetic) information content. Evolutionary divergence and reticulation are both significant parts of the evolutionary process that cannot be ignored in biological classification and that are necessary for high predictive quality.

Interpretation of patterns of genetic variation in endemic plant species of oceanic islands.

Oceanic islands offer special opportunities for understanding the patterns and processes of evolution. The availability of molecular markers in recent decades has enhanced these opportunities, facilitating the use of population genetics to reveal divergence and speciation in island systems. A common pattern seen in taxa on oceanic islands is a decreased level of genetic variation within and among populations, and the founder effect has often been invoked to explain this observation. Founder effects have a major impact on immigrant populations, but, over millions of years, the original genetic signature will normally be erased as a result of mutation, recombination, drift and selection. Therefore, the types and degrees of genetic modifications that occur must often be caused by other factors, which should be considered when explaining the patterns of genetic variation. The age of the island is extremely important because oceanic islands subside on their submarine plates over time. Erosion caused by wind, rain and wave action combine to grind down soft volcanic substrates. These geomorphological events can have a dramatic impact on population number and size, and hence levels of genetic diversity. The mode of speciation is also of significance. With anagenesis, genetic variation accumulates through time, whereas, with cladogenenesis, the gene pool splits into populations of adaptively radiating species. Breeding systems, population sizes and generation times are also important, as is hybridization between closely related taxa. Human disturbance has affected plant population number and size through the harvesting of forests and the introduction of invasive plants and animals. Therefore, the explanation of the observed levels of genetic variation in species of oceanic islands requires the consideration of many interconnected physical, biological and anthropomorphic factors.

Development of microsatellite markers in Robinsonia (Asteraceae) an endemic genus of the Juan Fernández Archipelago, Chile.

Ten microsatellite markers were developed for Robinsonia (Asteraceae), a genus endemic to the Juan Fernández Archipelago, Chile. Polymorphisms of these markers were tested using one population each of R. evenia, R. gayana, and R. gracilis. The number of alleles for these markers ranged from 2 to 17 per locus, and expected heterozygosity ranged from 0 to 0.847 by population. A significant deviation from Hardy-Weinberg equilibrium was observed in zero to two markers in each population, and no significant linkage disequilibrium between markers was detected. The markers reported here would be useful for evolutionary studies and conservation strategies in Robinsonia.

Genetic variation (AFLPs and nuclear microsatellites) in two anagenetically derived endemic species of Myrceugenia (Myrtaceae) on the Juan Fernández Islands, Chile.

PREMISE OF THE STUDY: Anagenesis (or phyletic evolution) is one mode of speciation that occurs in the evolution of plants on oceanic islands. Of two endemic species on the Juan Fernández Islands (Chile), Myrceugenia fernandeziana and M. schulzei (Myrtaceae), believed to have originated anagenetically from different continental progenitors, the first is endemic to Robinson Crusoe Island and has no clear tie to continental relatives; the last is endemic to the younger island, Alejandro Selkirk Island, and has close affinity to M. colchaguensis in mainland Chile. METHODS: Using AFLPs and six nuclear microsatellites from 381 individuals representing 33 populations, we determined patterns of genetic variation within and among populations on both islands and between those of the islands and mainland. KEY RESULTS: Considerable genetic variation was found within populations on both islands. The level of gene diversity within M. schulzei was equivalent to that of its close continental relative M. colchaguensis. Genetic diversity was not partitioned geographically in M. fernandeziana and was weakly so and nonsignificantly in M. schulzei. CONCLUSIONS: The high genetic variation in both taxa is most likely due to anagenetic speciation. Subsidence of the older island Robinson Crusoe, landscape erosion, and restructuring of communities have severely reduced the overall island population to a single panmictic system. On the younger and less modified Alejandro Selkirk Island, slightly stronger patterns of genetic divergence are seen in M. schulzei. Because both species are genetically diverse and number in the thousands of individuals, neither is presently endangered in the archipelago.

Anagenetic speciation in Ullung Island, Korea: genetic diversity and structure in the island endemic species, Acer takesimense (Sapindaceae).

Anagenetic speciation is an important mode of speciation in oceanic islands; one-fourth of the endemic plants are estimated to have been derived via this process. Few studies, however, have critically examined the genetic consequences of anagenesis in comparison with cladogenesis (involved with adaptive radiation). We hypothesize that endemic species originating via anagenetic speciation in a relatively uniform environment should accumulate genetic variation with limited populational differentiation. We undertook a population genetic analysis using nine nuclear microsatellite loci of Acer takesimense, an anagenetically derived species endemic to Ullung Island, Korea, and its continental progenitor A. pseudosieboldianum on the Korean Peninsula. Microsatellite data reveal a clear genetic distinction between the two species. A high F value in the cluster of A. takesimense was found by Bayesian clustering analysis, suggesting a strong episode of genetic drift during colonization and speciation. In comparison with A. pseudosieboldianum, A. takesimense has slightly lower genetic diversity and possesses less than half the number of private and rare alleles. Consistent with predictions, weak geographical genetic structure within the island was found in A. takesimense. These results imply that anagenetic speciation leads to a different pattern of specific and genetic diversity than often seen with cladogenesis.

Development of microsatellite markers in species of Erigeron (Asteraceae) endemic to the Juan Fernández Archipelago, Chile.

PREMISE OF THE STUDY: Microsatellite markers were developed in Erigeron rupicola and tested by amplification in six Erigeron species endemic to the Juan Fernández Archipelago, Chile, to investigate genetic diversity and population structure. • METHODS AND RESULTS: Using 454 pyrosequencing, 24 primer pairs were developed in E. rupicola, 12 of which amplified and presented polymorphism among endemic species of Erigeron in the Archipelago. Two populations from E. rupicola and E. fernandezianus were genotyped, and one to eight alleles per locus per population were detected. The expected heterozygosity ranged from 0.000 to 0.812. • CONCLUSIONS: These results indicate the utility of primers for cross-species populational studies in all endemic species of Erigeron in the Archipelago.

The evolutionary history of the white-rayed species of Melampodium (Asteraceae) involved multiple cycles of hybridization and polyploidization.

PREMISE OF THE STUDY: Polyploidy plays an important role in race differentiation and eventually speciation. Underlying mechanisms include chromosomal and genomic changes facilitating reproductive isolation and/or stabilization of hybrids. A prerequisite for studying these processes is a sound knowledge on the origin of polyploids. A well-suited group for studying polyploid evolution consists of the three species of Melampodium ser. Leucantha (Asteraceae): M. argophyllum, M. cinereum, and M. leucanthum. METHODS: The origin of polyploids was inferred using network and tree-based phylogenetic analyses of several plastid and nuclear DNA sequences and of fingerprint data (AFLP). Genome evolution was assessed via genome size measurements, karyotype analysis, and in situ hybridization of ribosomal DNA. KEY RESULTS: Tetraploid cytotypes of the phylogenetically distinct M. cinereum and M. leucanthum had, compared to the diploid cytotypes, doubled genome sizes and no evidence of gross chromosomal rearrangements. Hexaploid M. argophyllum constituted a separate lineage with limited intermixing with the other species, except in analyses from nuclear ITS. Its genome size was lower than expected if M. cinereum and/or M. leucanthum were involved in its origin, and no chromosomal rearrangements were evident. CONCLUSIONS: Polyploids in M. cinereum and M. leucanthum are of recent autopolyploid origin in line with the lack of significant genomic changes. Hexaploid M. argophyllum also appears to be of autopolyploid origin against the previous hypothesis of an allopolyploid origin involving the other two species, but some gene flow with the other species in early phases of differentiation cannot be excluded.