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Ranunculus section Batrachium (water crowfoot) ranks among the most taxonomically challenging aquatic plant groups due to morphological reduction, phenotypic plasticity, polyploidy and reticulate evolution. This study, for the first time in this group, linked morphology, genome size and genetic data (two non-coding regions of plastid DNA and the ITS region of nuclear ribosomal DNA). This extensive data set, including 258 central European populations, enables us to recognize widespread lineages from hybrids and to trace the evolutionary processes underlying the observed diversity. Most of the traditionally recognized species are supported. However, the presence of two morphologically cryptic but genetically well-differentiated lineages was detected within Ranunculus trichophyllus , and three separate lineages of different parentage were confirmed in the Ranunculus penicillatus complex. An allopolyploid origin was revealed in Ranunculus aquatilis , Ranunculus baudotii and in both lineages of R. trichophyllus , for which the parentage has not yet been studied, and allopolyploidy is suspected in all other polyploid taxa except for the triploid cytotype of Ranunculus fluitans , which is most likely autopolyploid. We detected putative F1 hybrids of seven different parentage combinations, including two involving Ranunculus rionii , representing the first known hybrids of this species. An additional 13 hybrid cytotypes (backcrosses or entailing additional polyploidization) were revealed; c. 20% of Ranunculus peltatus accessions seem to be influenced by introgression detectable only using sequence data. The Batrachium group is remarkable due to the coexistence of well-defined lineages with recently evolved biotypes arising due to hybridization and polyploidization. [ABSTRACT FROM AUTHOR]

Ochagavia (four species) and Fascicularia (one species) form a well-supported clade of the early-diverging Bromelioideae. The two genera are morphologically similar, but they can be easily discerned on the basis of generative characters. Besides the species distributed on the Chilean mainland, the group includes O. elegans , endemic to the Robinson Crusoe Island of the Juan Fernández Islands. In previous molecular phylogenetic studies, O. elegans formed a sister clade to the remainder of Fascicularia and Ochagavia. A phylogenomic approach, including nearly complete and, in five cases, full plastomes (c. 160 kbp) and the nuclear rDNA cistron (c. 6 kbp), and scanning electron microscope (SEM) images of pollen were used to analyse relationships in the Fascicularia-Ochagavia group. Plastome and nuclear trees were largely congruent and supported previous phylogenetic analyses of O. elegans being sister to the remainder of the group. A divergent phylogenetic position was suggested for O. carnea using different organellar trees. SEM analysis of pollen supported the division of Fascicularia and Ochagavia. Evolutionary and taxonomic implications of our results are discussed. [ABSTRACT FROM AUTHOR]

Ficaria is a taxonomically intriguing polyploid complex with high morphological variability. Both hybridization and polyploidization have been suggested as the main evolutionary forces behind the high morphological variability in this genus; however, detailed studies are lacking. In Central Europe, two Ficaria taxa (diploid F. calthifolia and tetraploid F. verna subsp. verna) occasionally co-occur in local sympatry, which might result in hybridization. We investigated sympatric populations of the two Ficaria taxa using flow cytometry, chromosome counts, AFLP analysis and plastid DNA sequencing; we also performed experimental homoploid and heteroploid crosses to determine the frequency and direction of hybrid triploid formation, an alternative route of triploid origin (autopolyploidy) and the possibility of a one-step neoallotetraploid origin. Sympatric populations were composed of three genetic clusters corresponding to diploid F. calthifolia (2 n = 16), tetraploid F. verna subsp. verna (2 n = 32) and triploid plants (2 n = 24). The holoploid genome size and AFLP data suggest a hybrid origin of the triploids, thereby making their formation via autopolyploidization in F. calthifolia unlikely. The triploid populations are monoclonal and of independent origin. In contrast, the parental populations exhibit high genotypic diversity and frequent sexual reproduction, including those of predominantly asexual F. verna subsp. verna. Experimental crossing confirmed that both parental taxa produce fertile seeds via a sexual pathway, but not by apomixis, and that both serve as pollen acceptors in heteroploid crosses, which is consistent with the plastid sequencing. However, hybridization is asymmetric, with maternal-excess crosses being significantly more successful. No signs of neoautotetraploidization or neoallotetraploidization were detected. In summary, recent gene flow between the studied Ficaria taxa is either limited or absent. [ABSTRACT FROM AUTHOR]

The non-native species of knotweeds (Fallopia sect. Reynoutria) are morphologically very similar and it is often difficult to distinguish between the hybrid F. ×bohemica and parental taxa, F. japonica and F. sachalinensis. To distinguish 30 samples of knotweeds, collected in Slovenia, we used PCR RFLP analysis of the trnK intron of plastid DNA in combination with the amplification of microsatellite nuclear locus KW6, which is a specific diagnostic marker for F. sachalinensis. We established that the combination of both markers unambiguously identifies the following samples: F. japonica (var. japonica), F. sachalinensis and F. ×bohemica. Based on described molecular markers we confirmed that the maternal parent of the taxon F. ×bohemica was F. japonica for all analysed hybrids. In addition, two species from Fallopia sect. Sarmentosae (F. baldschuanica and F. multiflora) were also analysed. Both could be distinguished from species of Fallopia sect. Reynoutria, but for the discrimination between them, some other markers should be used.

The genus Fagus (beech, Fagaceae) consists of about 10 species discontinuously distributed in East Asia, eastern North America, and Europe. Fagus multinervis occurs only on Ulleungdo Island, Korea, and is an important component of the island's plant community. The species was described primarily based on one of its stem characteristics: it branches at the base, producing several primary trunks. In part because no extant Fagus species are found in mainland Korea, and because the closest populations of Fagus are found in Japan, F. multinervis has been considered to be derived from the Japanese species, F. japonica. However, a recent study synonymized F. multinervis under F. engleriana and proposed that the beech population of Ulleungdo Island was derived instead from China via long-distance dispersal. Fagus multinervis is morphologically very similar to F. engleriana, but it can be distinguished by having rhombic lenticels that are vertically elongated. We determined the nucleotide sequences of the trnK-matK, trnL-trnF, trnH-psbA, and atpB-rbcL regions of plastid DNA and the second intron of the nuclear LEAFY gene from accessions of eight species, including eight F. multinervis individuals, in order to clarify the phylogenetic placement of this insular species. Phylogenetic analyses show that F. multinervis is monophyletic, and that it is closely related to F. engleriana and F. japonica. However, a sister relationship of F. multinervis with either of those species is not resolved. Therefore, our molecular data support the distinctness of F. multinervis as an endemic on Ulleungdo Island. Furthermore, incongruence between plastid and nuclear data suggests that F. multinervis may have originated via hybridization. [ABSTRACT FROM AUTHOR]

Inselberg-adapted species of bromeliads (Bromeliaceae) have been suggested as model systems for understanding the evolutionary genetics of species complexes and radiations in terrestrial, island-like environments. Bromeliads are particularly suitable for addressing the potential roles of interspecific gene exchange during plant speciation and radiation. We have studied populations of five narrowly endemic Alcantarea species adapted to high-elevation inselbergs of the Atlantic Rainforest of Brazil with nuclear and plastid DNA markers, estimated outcrossing rates in the giant bromeliad A. imperialis using progeny arrays and carried out a pilot study on the use of next generation sequencing-based genotyping in this group. Our results suggest widespread and asymmetric interspecific gene flow in the studied species complex, which visibly affects patterns of genetic diversity in the phenotypically variable mixed outcrosser A. imperialis. Our data support the hypothesis that gene flow has contributed to the origin of phenotypic forms in the A. imperialis s.l. species complex. We discuss potential conflicts between our neutral marker data and previous taxonomic work and suggest how these might be resolved. We close with a brief outlook on the potential of genomic tools to uncover the hidden links between genotypes, phenotypes and niches in bromeliads and other plant radiations. [ABSTRACT FROM AUTHOR]

The diploid aquatic genus Sparganium (Typhaceae) comprises ca. 14 species mainly in cool temperate regions of the world. Among these, S. emersum comprises two infraspecific taxa, subspecies acaule from eastern North America and subspecies emersum from Eurasia and western North America (and occasionally from eastern North America as well). However, there has been some discussion regarding the monophyly of S. emersum sensu lato. We tested the hypothesis of a polyphyletic S. emersum sensu lato in a phylogenetic framework. Sequence data from six plastid DNA regions and nuclear phyC were analyzed using maximum parsimony, maximum likelihood, and Bayesian inference. We obtained a moderately resolved phylogeny with the plastid DNA data set, while phylogenetically less-informative phyC was useful to distinguish morphological species and discern hybrid and non-hybrid specimens. Sparganium emersum sensu lato was resolved as polyphyletic, clustering with S. angustifolium and S. glomeratum, respectively. Sparganium acaule is resurrected to be a sister to S. glomeratum, for which synapomorphic and distinguishing morphological characters are provided. Three cases of hybridization were detected. [ABSTRACT FROM AUTHOR]

V eronica subsection P entasepalae is a diploid-polyploid complex of c. 20 species distributed in Eurasia and North Africa, in which species boundaries are difficult to determine. Here, we present the first comprehensive phylogenetic analysis of V. subsection P entasepalae based on nucleotide sequences [internal transcribed spacer ( ITS) and the plastid trnH-psbA and ycf6-psbM spacers] combined with ploidy estimations. Our results support the monophyly of the subsection. Five well-supported clades are recovered in the ITS sequence analyses, corresponding to broad geographical areas. The causes of the extensive incongruence found between the ITS and plastid DNA datasets, namely incomplete lineage sorting and/or hybridization and polyploidization, are discussed. Most of the diploids traditionally recognized based on morphological characters and one tetraploid are each recovered as monophyletic by the ITS sequence analyses. The Balkan species V . kindlii is resurrected. DNA ploidy level for V . teucrioides is reported here for the first time (2 x). Diploid populations have been found for V . orbiculata, which was previously thought to be only tetraploid. Past contact in the amphi- Adriatic area between V . orsiniana and V . orbiculata is suggested. Finally, molecular analyses show that diploid V . jacquinii and diploid V . orbiculata are unrelated. This study contributes to our understanding of the evolutionary history of polyploid complexes, especially those in southern Europe, and highlights the importance of using multiple lines of evidence to investigate species boundaries in such actively diversifying groups. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 179, 670-692. [ABSTRACT FROM AUTHOR]

Recent molecular phylogenetic studies reported high diversity of Ruppia species in the Mediterranean. Multiple taxa, including apparent endemics, are known from that region, however, they have thus far not been exposed to phylogenetic analyses aimed at studying their relationships to taxa from other parts of the world. Here we present a comprehensive phylogenetic analyses of the R. maritima complex using data sets composed of DNA sequences of the plastid genome, the multi-copy nuclear ITS region, and the low-copy nuclear phyB gene with a primary focus on the Mediterranean representatives of the complex. As a result, a new lineage, 'Drepanensis', was identified as the seventh entity of the complex. This lineage is endemic to the Mediterranean. The accessions included in the former 'Tetraploid' entity were reclassified into two entities: an Asia-Australia-Europe disjunct 'Tetraploid_α' with a paternal 'Diploid' origin, and a European 'Tetraploid_γ' originating from a maternal 'Drepanensis' lineage. Another entity, 'Tetraploid_β', is likely to have been originated as a result of chloroplast capture through backcrossing hybridization between paternal 'Tetraploid_α' and maternal 'Tetraploid_γ'. Additional discovery of multiple tetraploidizations as well as hybridization and chloroplast capture at the tetraploid level indicated that hybridization has been a significant factor in the diversification of Ruppia. [ABSTRACT FROM AUTHOR]

Highlights: [•] Phylogenetic analysis of nrITS sequences of Galanthus provides a well-resolved topology. [•] Seven major clades are defined: Platyphyllus, Trojanus, Ikariae, Elwesii, Nivalis, Woronowii, and Alpinus. [•] Phylogenetic network analysis identifies several possible hybridization events. [•] Incongruence between ITS and plastid data are more likely due to lack of resolution in the plastid data. [•] Some Galanthus species are in need of taxonomic recircumscription. [ABSTRACT FROM AUTHOR]

Little is known about the contribution of interspecific hybridization, a frequent phenomenon in plants, to the high plant diversity in southeastern Europe, one of the continent's diversity hot spots. A good system to study the relevance of hybridization for biodiversity in this region is Veronica subg. Pseudolysimachium sect. Pseudolysimachion (Plantag- inaceae). Depending on the presumed frequency of hybridization, existing taxonomic concepts in this group range from distinguishing only morphological races without explicit taxonomic status to recognizing several species each with a series of intraspecific taxa. Using genetic (plastid sequences and AFLP fingerprints), ploidy-level and morphometric data, three core groups, pertaining to the currently recognized species V barrelieri, V orchidea, and V spicata, were identified. All three species are, however, connected by numerous and gradual genotypic transitions and show rampant discrepancies between genetic and morphometric-taxonomic assignments. Complete homogenization of the three core groups is probably prevented by geographic isolation, ecological divergence and ploidy differences. Misinterpretation of hybrid swarms as separate taxa and the mosaic distribution of different indumentum types have led to a gross overestimation of taxonomic diversity of V sect. Pseudolysimachion in southeastern Europe. Taxonomically, this might be accommodated by reducing V barrelieri, V orchidea and V spicata to subspecific rank and abandoning recognition at least of those subspecies and varieties included in our study. [ABSTRACT FROM AUTHOR]

The closely related dioecious herbs Silene latifolia and Silene dioica are widespread and predominantly sympatric in Europe. The species are interfertile, but morphologically and ecologically distinct. A study of large-scale patterns of plastid DNA (polymerase chain reaction–restriction fragment length polymorphism) haplotypes in a sample of 198 populations from most of the European ranges of both species revealed extensive interspecific haplotype sharing. Four of the 28 detected haplotypes were frequent (found in > 40 populations) and widespread. Three of these frequent haplotypes occurred in both species and the geographic distribution of each haplotype was broadly congruent in both species. Each of these three, shared and widespread haplotypes is likely to have colonized central and/or northern Europe after the last glaciation from one or more of refugial areas in southern Europe. Interspecific hybridization and plastid introgression within refugial regions and/or during the early stages of postglacial expansion is the most plausible explanation for the broadly similar distribution patterns of the shared, frequent chloroplast haplotypes in the two species. The fourth frequent, widespread haplotype was absent from S. latifolia and almost entirely restricted to Nordic S. dioica. It is most likely that this haplotype spread into the Nordic countries from a central or northern European source or from a refugial area in Russia. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 161, 153–170. [ABSTRACT FROM AUTHOR]

Eight variable regions (microsatellites, insertion/deletion and duplication regions) from the plastid DNA genome were analyzed for 91 populations belonging to Dactylorhiza majalis ssp. traunsteineri and closely related taxa. A total of 36 composite plastid haplotypes were found. The two dominating haplotypes had a clear geographic distribution suggesting at least two separate immigration routes into Scandinavia after the last glaciation: one southwestern route and one or two southeastern routes. D. majalis ssp. traunsteineri could not be clearly separated from any of the other taxa included in the study except for D. majalis ssp. sphagnicola. The morphologically similar taxa D. majalis ssp. traunsteineri, D. majalis ssp. lapponica and D. majalis ssp. russowii showed no genetic differentiation, and therefore we suggest an amalgamation of the three taxa into one broadly circumscribed subspecies; D. majalis ssp. lapponica. The plastid data also revealed incidents of hybridization and possible introgression between D. majalis ssp. lapponica and other members of the genus, e.g., D. incarnata. [ABSTRACT FROM AUTHOR]

The Dactylorhiza incarnata/ maculata complex (Orchidaceae) was used as a model system to understand genetic differentiation processes in a naturally occurring polyploid complex with much of ongoing diversification and wide distribution in recently glaciated areas in northern Europe. Data were obtained for 12 hypervariable regions in the plastid DNA genome. A total of 166 haplotypes were found in a sample of 1099 plants. Allopolyploid taxa have inherited their plastid genomes from D. maculata s.l. Overall haplotype diversity of the combined group of allopolyploid taxa was comparable to that of maternal D. maculata s.l., but populations of allopolyploids were also more strongly differentiated from each other and contained lower numbers of haplotypes than populations of D. maculata s.l. In addition to haplotypes found in extant D. maculata s.l., the allopolyploids also contained several distinct and widespread haplotypes that were not found in any of the parental lineages. Some of these haplotypes were shared between widespread allopolyploids. Divergent allopolyploids with small distributions did not seem to originate from local polyploidization events, but rather as segregates of already existing allopolyploids. Genetic diversification of allopolyploid Dactylorhiza is the result of repeated polyploid formation, secondary hybridization and introgression between already existing polyploids and extant representatives of parental lineages, hybridization between independently derived polyploid lineages, and phyletic diversification in the group of allopolyploids. Although some polyploid taxa must have evolved after the last glaciation, genetic material from the parental lineages has been transferred continuously for longer periods of time. This combination of processes may explain the taxonomic complexity encountered in Dactylorhiza and other polyploid complexes distributed in previously glaciated parts of Europe. [ABSTRACT FROM AUTHOR]

The olive tree (Olea europaea) has successfully invaded several regions in Australia and Pacific islands. Two olive subspecies (subspp. europaea and cuspidata) were first introduced in these areas during the nineteenth century. In the present study, we determine the origin of invasive olives and investigate the importance of historical effects on the genetic diversity of populations. Four invasive populations from Australia and Hawaii were characterized using eight nuclear DNA microsatellites, plastid DNA markers as well as ITS-1 sequences. Based on these data, their genetic similarity with native populations was investigated, and it was determined that East Australian and Hawaiian populations (subsp. cuspidata) have originated from southern Africa while South Australian populations (subsp. europaea) have mostly derived from western or central Mediterranean cultivars. Invasive populations of subsp. cuspidata showed significant loss of genetic diversity in comparison to a putative source population, and a recent bottleneck was evidenced in Hawaii. Conversely, invasive populations of subsp. europaea did not display significant loss of genetic diversity in comparison to a native Mediterranean population. Different histories of invasion were inferred for these two taxa with multiple cultivars introduced restoring gene diversity for europaea and a single successful founder event and sequential introductions to East Australia and then Hawaii for cuspidata. Furthermore, one hybrid (cuspidata × europaea) was identified in East Australia. The importance of hybridizations in the future evolution of the olive invasiveness remains to be investigated.Heredity (2007) 99, 608–619; doi:10.1038/sj.hdy.6801037; published online 8 August 2007 [ABSTRACT FROM AUTHOR]

A new nothosubspecies Cirsium × vivantii is described after a molecular and morphological characterization of eight individuals collected in two separate valleys of the French central Pyrenees. Both hypervariable Amplified Fragment Length Polymorphism (AFLP) markers and nuclear rDNA (ITS) and plastid ( trnL-F, TRNT-L) DNA sequences were analysed. The profiles of these hybrid samples were compared to those of 43 individuals belonging to their presumed parental taxa C. carniolicum ssp. rufescens and C. palustre. A total of 133 AFLP bands were scored from three primer-pair combinations. All 130 AFLP bands that amplified in the hybrid samples were present in either C. carniolicum ssp. rufescens, C. palustre or both taxa, supporting the participation of these plant genomes in the resulting hybrids. Several Additive Polymorphic Sites (APS) detected in the ITS sequences of the hybrid samples also confirmed their derived origins from ribotypes of the two parental taxa. The lack of exclusive AFLP markers and the nonconcerted evolution of rDNA polymorphisms towards either of the parental ribotypes indicated their recent origin. Plastid trnT-L sequences were used to identify C. palustre as the maternal parent of six of these hybrid individuals; either parent could have acted as the plastid genome donor for the other two individuals. The morphological study revealed that all hybrid individuals were morphologically intermediate between their parents showing largely lobed and less spiny basal leaves as in C. carniolicum ssp. rufescens and decurrent leaf bases and pinkish corollas as in C. palustre. © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 154, 421–434. [ABSTRACT FROM AUTHOR]

The parentage of polyploid Sorbus species in the British Isles was investigated using plastid DNA microsatellites. Four hundred and fifty-three samples from 30 taxa were screened using six microsatellite fragments, which gave 28 haplotypes. The haplotypes formed groups clearly related to the ancestral diploids Sorbus aria, Sorbus aucuparia, and Sorbus torminalis. Species in the Sorbus aria group all had Aria haplotypes (with the exception of one English S. aria), species in the Sorbus anglica group had an Aucuparia haplotype, and species in the Sorbus latifolia group had a Torminalis haplotype. Sorbus intermedia had an Aucuparia haplotype. This indicated that the hybridization events that led to the formation of species in the S. anglica and S. latifolia groups usually did so with S. aria s.l. as the pollen-donating (paternal) parent. The polyploids S. anglica, Sorbus bristoliensis, Sorbus croceocarpa, Sorbus decipiens, Sorbus devoniensis, Sorbus hibernica, Sorbus lancastriensis, Sorbus leptophylla, Sorbus leyana, Sorbus minima, Sorbus rupicola, Sorbus subcuneata, Sorbus vexans, Sorbus whiteana, Sorbus wilmottiana, and three unnamed taxa may each be derived from a single maternal lineage. The polyploids Sorbus eminens, Sorbus porrigentiformis, and S. latifolia have multiple maternal lineages. The two primary diploid hybrids S. × thuringiaca and S. × vagensis have arisen many times independently. © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 154, 291–304. [ABSTRACT FROM AUTHOR]

Aim The olive tree is considered one of the best indicators of the Mediterranean climate. The species’ distribution is associated with geographical and bioclimatic factors, as well as being influenced by a long period of cultivation. Despite concerted efforts of different research groups, the origin of the Mediterranean olive tree still remains elusive. In the present study, relationships between taxa and populations covering the entire range of Olea europaea were investigated using both maternal (plastid genome) and biparental (nuclear genome) markers to disclose evolutionary patterns in the olive complex. Phylogenetic and phylogeographical results of the two-genome analyses were interpreted in a biogeographical context. Location Mediterranean, temperate and subtropical floristic regions of the Old World. Methods Phylogeographical reconstructions of plastid DNA polymorphism were performed using microsatellites, restriction sites and indels on a wide sample of 185 representative trees across the Old World, including 28 herbarium specimens from remote areas. Additionally, the potential utility of one ITS-1 pseudogene for phylogenetic analyses was explored using Bayesian and maximum parsimony approaches on a subsample of 38 olive trees. Results Forty plastid haplotypes were recognized and split into two lineages and seven sublineages. The analysis of ITS-1 sequences also allowed the identification of seven well differentiated groups. Distribution of plastid and ribosomal DNA lineages was congruent, but particular cases of phylogenetic incongruence were disclosed (particularly in the Sahara and Madeira). Lastly, two divergent ITS-1 copies were isolated from the same sample of four individuals of different subspecies. Main conclusions Phylogenetic congruence of both ITS-1 and plastid lineages suggested an evolutionary scenario of predominant isolation during the Plio-Pleistocene in Macaronesia, the Mediterranean, southern Africa, eastern Africa and Asia. The Saharan desert appeared to have played an important role of vicariant barrier between southern and northern African populations in early times. Incongruence of some plastid and nuclear results, as well as intermingled ITS-1 copies of different lineages in single individuals, was interpreted as a result of recurrent reticulation events in the olive complex. We identified an ancient hybrid zone from the Sahara to north-eastern African mountains, where divergent plastid and nuclear lineages still co-exist. Results of this paper, and previous studies, suggest that the cultivated olive originated from a pre-Quaternary Mediterranean ancestor, with no evidence for a recent hybrid origin. In contrast, a continuous process of olive domestication through local hybridization events of cultivated trees with natural populations may have brought about a remarkably high genomic diversity among cultivated trees across the Mediterranean. [ABSTRACT FROM AUTHOR]

The renewed interest in the use of hybrid zones for studying speciation calls for the identification and study of hybrid zones across a wide range of organisms, especially in long-lived taxa for which it is often difficult to generate interpopulation variation through controlled crosses. Here, we report on the extent and direction of introgression between two members of the‘model tree’ genusPopulus:Populus alba(white poplar) andPopulus tremula(European aspen), across a large zone of sympatry located in the Danube valley. We genotyped 93 hybrid morphotypes and samples from four parental reference populations from within and outside the zone of sympatry for a genome-wide set of 20 nuclear microsatellites and eight plastid DNA restriction site polymorphisms. Our results indicate that introgression occurs preferentially fromP. tremulatoP. albaviaP. tremulapollen. This unidirectional pattern is facilitated by high levels of pollen vs. seed dispersal inP. tremula(pollen/seed flow = 23.9) and by great ecological opportunity in the lowland floodplain forest in proximity toP. albaseed parents, which maintains gene flow in the direction ofP. albadespite smaller effective population sizes (N e) in this species (P. alba N e c.500–550;P. tremula N e c.550–700). Our results indicate that hybrid zones will be valuable tools for studying the genetic architecture of the barrier to gene flow between these two ecologically divergentPopulusspecies. [ABSTRACT FROM AUTHOR]

Abstract To obtain further information on the polyploid dynamics of the the Dactylorhiza incarnata/maculata polyploid complex and the origin of the allotetraploid D. sphagnicola (Orchidaceae), plastid DNA variation was studied in 400 plants from from Sweden and elsewhere in Europe and Asia Minor by means of polymerase chain reaction–restriction fragment length polymorphisms (PCR-RFLPs) and sequencing. Allotetraploid taxa in Europe are known have evolved by multiple independent polyploidization events following hybridization between the same set of two distinct ancestral lineages. Most allotetraploids have inherited the plastid genome from parents similar to D. maculata sensu lato , which includes, e.g. the diploid D. fuchsii and the autotetraploid D. maculata sensu stricto . D. sphagnicola carries a separate plastid haplotype different from the one found in other allotetraploid taxa, which is in agreement with an independent origin from the parental lineages. Some of the remaining allotetraploids have local distributions and appear to be of postglacial origin, whereas still other allotetraploids may be of higher age, carrying plastid haplotypes that have not been encountered in present day representatives of the parental lineages. Introgression and hybridization between diploids and allotetraploids, and between different independently derived allotetraploids may further have contributed to genetic diversity at the tetraploid level. Overall, the Dactylorhiza polyploid complex illustrates how taxon diversity and genetic diversity may be replenished rapidly in a recently glaciated area. [ABSTRACT FROM AUTHOR]