A conceptual framework to untangle the concept of urban ecosystem services.

Urban ecosystem service (UES) is becoming an influential concept to guide the planning, design, and management of urban landscapes towards urban sustainability. However, its use is hindered by definitional ambiguity, and the conceptual bases underpinning its application remain weak. This is exemplified by two different but equally valid interpretations of UES: "urban ecosystem services", referring to ecosystem services from analogs of natural and semi-natural ecosystems within urban boundaries, and "urban ecosystem services", a much broader term that includes the former group as well as urban services in a city. While we recognize that a single definition of UES is not possible nor necessary as its application is context-dependent, it is nevertheless useful to clarify the relationships between these interpretations to promote consistent use, and importantly, explore how a broader interpretation of UES might advance its applications in areas that have been neglected. We developed a conceptual framework that links UES to natural and human-derived capital to explain the relationships between the dual meanings of UES and proposed three normative propositions to guide its application: (1) integrate holistically multiple components of natural capital to provide UES, (2) reduce dependence on non-renewable abiotic resources and human-derived capital, and (3) enhance UES through technology. The framework we developed helps to resolve the current ambiguity in the meanings of UES, highlights the need to recognise neglected aspects of natural capital important for UES, and can be used to clarify relationships with related concepts conveying dependence of human well-being on nature.

Trait differentiation and adaptation of plants along elevation gradients.

Studies of genetic adaptation in plant populations along elevation gradients in mountains have a long history, but there has until now been neither a synthesis of how frequently plant populations exhibit adaptation to elevation nor an evaluation of how consistent underlying trait differences across species are. We reviewed studies of adaptation along elevation gradients (i) from a meta-analysis of phenotypic differentiation of three traits (height, biomass and phenology) from plants growing in 70 common garden experiments; (ii) by testing elevation adaptation using three fitness proxies (survival, reproductive output and biomass) from 14 reciprocal transplant experiments; (iii) by qualitatively assessing information at the molecular level, from 10 genomewide surveys and candidate gene approaches. We found that plants originating from high elevations were generally shorter and produced less biomass, but phenology did not vary consistently. We found significant evidence for elevation adaptation in terms of survival and biomass, but not for reproductive output. Variation in phenotypic and fitness responses to elevation across species was not related to life history traits or to environmental conditions. Molecular studies, which have focussed mainly on loci related to plant physiology and phenology, also provide evidence for adaptation along elevation gradients. Together, these studies indicate that genetically based trait differentiation and adaptation to elevation are widespread in plants. We conclude that a better understanding of the mechanisms underlying adaptation, not only to elevation but also to environmental change, will require more studies combining the ecological and molecular approaches.

The nutrient economy of Lodoicea maldivica, a monodominant palm producing the world's largest seed.

The iconic Lodoicea maldivica palm appears to invest heavily in reproduction, with females bearing the world's largest seeds and males producing copious pollen. We asked how these palms, which grow in extremely poor soils, obtain sufficient nutrients to support such high levels of reproductive function. Our study site was the Vallée de Mai UNESCO Site on Praslin, Seychelles. We measured the trees' allocations of dry matter, nitrogen (N) and phosphorus (P) to aboveground growth and reproduction, quantified stemflow and throughfall, and measured availabilities of N and P in the soil. We show that the nutrient costs of reproduction are very high in male and female plants, and for P far exceed those of vegetative growth. We describe how the palm leaves form a huge funnel that intercepts particulate material, especially pollen, which is flushed to the base of the trunk when it rains. In this way, Lodoicea improves its nutrient supply and that of its dispersal-limited offspring. Lodoicea shares many functional characteristics with dominant trees of other monodominant forests in the humid tropics. It also exhibits unique features, including its huge seed, effective funnelling mechanism and diverse community of closely associated animals, suggesting a long evolutionary history under relatively stable conditions.

Assembly of nonnative floras along elevational gradients explained by directional ecological filtering.

Nonnative species richness typically declines along environmental gradients such as elevation. It is usually assumed that this is because few invaders possess the necessary adaptations to succeed under extreme environmental conditions. Here, we show that nonnative plants reaching high elevations around the world are not highly specialized stress tolerators but species with broad climatic tolerances capable of growing across a wide elevational range. These results contrast with patterns for native species, and they can be explained by the unidirectional expansion of nonnative species from anthropogenic sources at low elevations and the progressive dropping out of species with narrow elevational amplitudes--a process that we call directional ecological filtering. Independent data confirm that climatic generalists have succeeded in colonizing the more extreme environments at higher elevations. These results suggest that invasion resistance is not conferred by extreme conditions at a particular site but determined by pathways of introduction of nonnative species. In the future, increased direct introduction of nonnative species with specialized ecophysiological adaptations to mountain environments could increase the risk of invasion. As well as providing a general explanation for gradients of nonnative species richness and the importance of traits such as phenotypic plasticity for many invasive species, the concept of directional ecological filtering is useful for understanding the initial assembly of some native floras at high elevations and latitudes.

Methane transport and emissions from soil as affected by water table and vascular plants.

BACKGROUND: The important greenhouse gas (GHG) methane is produced naturally in anaerobic wetland soils. By affecting the production, oxidation and transport of methane to the atmosphere, plants have a major influence upon the quantities emitted by wetlands. Different species and functional plant groups have been shown to affect these processes differently, but our knowledge about how these effects are influenced by abiotic factors such as water regime and temperature remains limited. Here we present a mesocosm experiment comparing eight plant species for their effects on internal transport and overall emissions of methane under contrasting hydrological conditions. To quantify how much methane was transported internally through plants (the chimney effect), we blocked diffusion from the soil surface with an agar seal. RESULTS: We found that graminoids caused higher methane emissions than forbs, although the emissions from mesocosms with different species were either lower than or comparable to those from control mesocosms with no plant (i.e. bare soil). Species with a relatively greater root volume and a larger biomass exhibited a larger chimney effect, though overall methane emissions were negatively related to plant biomass. Emissions were also reduced by lowering the water table. CONCLUSIONS: We conclude that plant species (and functional groups) vary in the degree to which they transport methane to the atmosphere. However, a plant with a high capacity to transport methane does not necessarily emit more methane, as it may also cause more rhizosphere oxidation of methane. A shift in plant species composition from graminoids to forbs and/or from low to high productive species may lead to reduction of methane emissions.

Mate-choice for close kin is associated with improved offspring survival in Lodoicea maldivica, the largest-seeded plant in the world.

We studied spatial patterns of kinship in the offspring of the endangered Lodoicea maldivica, a dioecious palm that produces the largest seed of any plant. Previous research has suggested that restricted seed and pollen dispersal in populations resulted in strong spatial genetic structure. We used microsatellites to genotype young plants and their potential parents at four sites across the species' entire natural range. We determined the most likely parents of each young plant based on the spatial separation of each parent pair, their genetic relatedness, and the level of correlated paternity. We identified both parents (43 female, 54 male) for 139 of 493 young plants. Mean distance between parental pairs was 26.8 m. Correlated paternity was low (0.168), indicating that mother trees were often pollinated by several fathers. Parental pairs were more closely related than expected by chance, suggesting outbreeding depression. Our results highlight the apparent strong mate choice for close kin in parent pairs of surviving offspring. We discuss the alternative biological processes that could lead to this, including the potential for break-up of favourable allelic combinations necessary for the development of the palm's very large seed. Management implications include germinating seeds where they naturally fall, using a diverse range of male plants as pollen donors for hand pollination, and protecting the native community of gecko pollinators.

Ideas, concerns, expectations, and effects on life (ICEE) in GP consultations: an observational study using video-recorded UK consultations.

BACKGROUND: Eliciting patients' ideas, concerns, expectations, and whether a problem has an 'effect' on their life (ICEE), is a widely recommended communication technique. However, it is not known how frequently ICEE components are raised in UK GP consultations. AIM: To assess the frequency of ICEE in routine GP consultations with adult patients and explore variables associated with ICEE. DESIGN & SETTING: An observational study was undertaken. It involved secondary analysis of a pre-existing archive of video-recorded, face-to-face GP consultations in the UK. METHOD: Observational coding of 92 consultations took place. Associations were assessed using binomial and ordered logistic regression. RESULTS: Most consultations included at least one ICEE component (90.2%). The most common ICEE component per consultation was patient ideas (79.3%), followed by concerns (55.4%), expectations (51.1%), and then effects on life (42.4%). For all ICEE components patients more commonly initiated the ICEE dialogue, and in only three consultations (3.3%) did GPs directly ask patients about their expectations. Problems that were acute (odds ratio [OR] 2.98, 95% confidence interval [CI] = 1.36 to 6.53, P = 0.007) or assessed by GPs aged ≥50 years (OR 2.10, 95% CI = 1.07 to 4.13, P = 0.030) were associated with more ICEE components. Problems assessed later in the consultation (OR 0.60 per problem order increase, 95% CI = 0.41 to 0.87, P = 0.007) by patients aged ≥75 years (OR 0.40, 95% CI = 0.16 to 0.98, P = 0.046) and from the most deprived cohort (OR 0.39, 95% CI = 0.17 to 0.92, P = 0.032) were associated with fewer ICEE components. Patient ideas were associated with more patients being 'very satisfied' post-consultation (OR 10.74, 95% CI = 1.60 to 72.0, P = 0.014) and the opposite was true of concerns (OR 0.14, 95% CI = 0.02 to 0.86, P = 0.034). CONCLUSION: ICEE components were associated with patient satisfaction and demographic variables. Further research is required to assess if the way ICEE are communicated affects these associations and other potential confounders.

Alien and endangered plants in the Brazilian Cerrado exhibit contrasting relationships with vegetation biomass and N : P stoichiometry.

Although endangered and alien invasive plants are commonly assumed to persist under different environmental conditions, surprisingly few studies have investigated whether this is the case. We examined how endangered and alien species are distributed in relation to community biomass and N : P ratio in the above-ground community biomass in savanna vegetation in the Brazilian Cerrado. For 60 plots, we related the occurrence of endangered (Red List) and alien invasive species to plant species richness, vegetation biomass and N : P ratio, and soil variables. Endangered plants occurred mainly in plots with relatively low above-ground biomass and high N : P ratios, whereas alien invasive species occurred in plots with intermediate to high biomass and low N : P ratios. Occurrences of endangered or alien plants were unrelated to extractable N and P concentrations in the soil. These contrasting distributions in the Cerrado imply that alien species only pose a threat to endangered species if they are able to invade sites occupied by these species and increase the above-ground biomass and/or decrease the N : P ratio of the vegetation. We found some evidence that alien species do increase above-ground community biomass in the Cerrado, but their possible effect on N : P stoichiometry requires further study.

Genetically based differentiation in growth of multiple non-native plant species along a steep environmental gradient.

A non-native plant species spreading along an environmental gradient may need to adjust its growth to the prevailing conditions that it encounters by a combination of phenotypic plasticity and genetic adaptation. There have been several studies of how non-native species respond to changing environmental conditions along latitudinal gradients, but much less is known about elevational gradients. We conducted a climate chamber experiment to investigate plastic and genetically based growth responses of 13 herbaceous non-native plants along an elevational gradient from 100 to 2,000 m a.s.l. in Tenerife. Conditions in the field ranged from high anthropogenic disturbance but generally favourable temperatures for plant growth in the lower half of the gradient, to low disturbance but much cooler conditions in the upper half. We collected seed from low, mid and high elevations and grew them in climate chambers under the characteristic temperatures at these three elevations. Growth of all species was reduced under lower temperatures along both halves of the gradient. We found consistent genetically based differences in growth over the upper elevational gradient, with plants from high-elevation sites growing more slowly than those from mid-elevation ones, while the pattern in the lower part of the gradient was more mixed. Our data suggest that many non-native plants might respond to climate along elevational gradients by genetically based changes in key traits, especially at higher elevations where low temperatures probably impose a stronger selection pressure. At lower elevations, where anthropogenic influences are greater, higher gene flow and frequent disturbance might favour genotypes with broad ecological amplitudes. Thus the importance of evolutionary processes for invasion success is likely to be context-dependent.

Factors affecting the documentation of spoken safety-netting advice in routine GP consultations: a cross-sectional study.

BACKGROUND: Previous studies have reported how often safety-netting is documented in medical records, but it is not known how this compares with what is verbalised and what factors might influence the consistency of documentation. AIM: To compare spoken and documented safety-netting advice and to explore factors associated with documentation. DESIGN AND SETTING: A cross-sectional study, using an existing GP consultations archive. METHOD: Observational coding involving classifying and quantifying medical record entries and comparison with spoken safety-netting advice in 295 video-/audio-recorded consultations. Associations were tested using logistic regression. RESULTS: Two-thirds of consultations (192/295) contained spoken safety-netting advice that applied to less than half of the problems assessed (242/516). Only one-third of consultations (94/295) had documented safety-netting advice, which covered 20.3% of problems (105/516). The practice of GPs varied widely, from those that did not document their safety-netting advice to those that nearly always did so (86.7%). GPs were more likely to document their safety-netting advice for new problems (P = 0.030), when only a single problem was discussed in a consultation (P = 0.040), and when they gave specific rather than generic safety-netting advice (P = 0.007). In consultations where multiple problems were assessed (n = 139), the frequency of spoken and documented safety-netting advice decreased the later a problem was assessed. CONCLUSION: GPs frequently do not document the safety-netting advice they have given to patients, which may have medicolegal implications in the event of an untoward incident. GPs should consider how safely they can assess and document more than one problem in a single consultation and this risk should be shared with patients to help manage expectations.

Why only tetraploid Solidago gigantea (Asteraceae) became invasive: a common garden comparison of ploidy levels.

Many studies have compared the growth of plants from native and invasive populations, but few have considered the role of ploidy. In its native range in North America, Solidago gigantea Aiton (Asteraceae) occurs as a diploid, tetraploid and hexaploid, with considerable habitat differentiation and geographic separation amongst these ploidy levels. In the introduced range in Europe, however, only tetraploid populations are known. We investigated the growth performance and life history characteristics of plants from 12 European and 24 North American (12 diploid, 12 tetraploid) populations in a common garden experiment involving two nutrient and two calcium treatments. Twelve plants per population were grown in pots for two seasons. We measured 24 traits related to leaf nutrients, plant size, biomass production and phenology as well as sexual and vegetative reproduction. Native diploid plants had a higher specific leaf area and higher leaf nutrient concentrations than native tetraploids, but tetraploids produced many more shoots and rhizomes. Diploids grown with additional calcium produced less biomass, whereas tetraploids were not affected. European plants were less likely to flower and produced smaller capitulescences than North American tetraploids, but biomass production and shoot and rhizome number did not differ. We conclude that a knowledge of ploidy level is essential in comparative studies of invasive and native populations. While clonal growth is important for the invasion success of tetraploid S. gigantea, its potential was not acquired by adaptation after introduction but by evolutionary processes in the native range.

The content and conduct of GP consultations for dermatology problems: a cross-sectional study.

BACKGROUND: Skin complaints are common in primary care, and poor outcomes in long-term conditions are often due to low adherence to treatment. Shared decision making and self-management support may help, yet there is little understanding of patient involvement or the support provided by GPs. AIM: To describe the content of primary care consultations for skin problems, including shared decision making practice, delivery of self-management advice, and follow-up. DESIGN AND SETTING: Cross-sectional study of video-recorded UK adult GP consultations and linked data. METHOD: A coding tool was developed and applied to all consultations with skin problems. Shared decision making was assessed using the observer OPTION5 scale. RESULTS: A total of 45/318 consultations (14.2%) related to one or more skin problems, which were discussed alongside other problems in 71.1% (32/45) of consultations. Of the 100 different problems discussed in these consultations, 51 were dermatological. The mean amount of time spent on skin problems in the consultations was 4 minutes 16 seconds. Medication was recommended for 66.7% (34/51) of skin problems, with low shared decision making (mean OPTION5 score = 10.7). Self-management advice (verbal only) was given for 47.1% (24/51) of skin problems. Most skin problems (84.3%; 43/51) were not referred to secondary care; 32.6% (14/43) of the skin problems not referred were seen again in primary care within 12 weeks, of which 35.7% (5/14) follow-up appointments were not planned. CONCLUSION: In this study, skin problems were usually presented alongside other complaints and resulted in a medication recommendation. Shared decision making was uncommon and self-management advice not consistently given, with re-attendance for the same problem common. GPs' training should reflect how frequently skin problems are seen and seek to improve patient involvement in decision making and support self-management.

Species richness both impedes and promotes alien plant invasions in the Brazilian Cerrado.

Worldwide, alien plant invasions have been intensively studied in the past decades, but mechanisms controlling the invasibility of native communities are not fully understood yet. The stochastic niche hypothesis predicts that species-rich plant communities are less prone to alien plant invasions than species-poor communities, which is supported by some but not all field studies, with some very species-rich communities such as the Brazilian Cerrado becoming heavily invaded. However, species-rich communities potentially contain a greater variety of facilitative interactions in resource exploitation than species-poor communities, from which invasive plants might benefit. This alternative hypothetical mechanism might explain why nutrient-poor, species-rich ecosystems are prone to invasion. Here we show that a high species richness both impedes and promotes invasive plants in the Brazilian Cerrado, using structural equation modelling and data from 38 field sites. We found support for the stochastic niche hypothesis through an observed direct negative influence of species richness on abundance of alien invasive species, but an indirect positive effect of species richness on invasive alien plants through soil phosphatase activity that enhances P availability was also found. These field observations were supported with results from a mesocosm experiment. Root phosphatase activity of plants increased with species richness in the mesocosms, which was associated with greater community P and N uptake. The most prominent alien grass species of the region, Melinis minutiflora, benefited most from the higher N and P availability in the species mixtures. Hence, this study provides a novel explanation of why species-richness may sometimes promote rather than impede invasion, and highlights the need to perform facilitation experiments in multi-species communities.

Demographic biases in engagement with nature in a tropical Asian city.

Urban residents can benefit from spending time in outdoor spaces and engaging with nature-related activities. Such engagement can improve health and well-being, support community cohesion, and improve environmentally-friendly behaviours. However, engagement with nature may not be equal amongst different members of society. We investigated individual variation in engagement with nature in Singapore, a high-density city in tropical Southeast Asia. Through a survey of 1000 residents, we analysed relationships between demographic factors such as age, income, and sex, and the frequency of visitation to different ecosystem types, and the frequency of engagement with different nature-related activities. Parks and neighbourhood open spaces were among the most commonly-visited outdoor spaces, with nature reserves and other natural areas being visited less frequently. Common activities included sitting outdoors, art and photography, and running, while hiking and nature recreation were less frequent. In contrast with previous studies, we found relatively small differences among different groups of the population in their preferred types of outdoor activities. Older people, those with lower incomes, and without degrees were less likely to visit most types of outdoor space and engage with most types of nature-related activities. In the case of nature reserves, the distance from the visitor's home had a significantly negative influence on the frequency of visitation. These findings demonstrate that the benefits of engagement with nature are not equally enjoyed by all demographic groups, and that some groups lack engagement across the board. Strategies to increase nature engagement in tropical cities could include increasing the local availability and accessibility of different types of outdoor space, and education and public outreach programmes to encourage participation.

Identification of sex-linked markers in the sexually cryptic coco de mer: are males and females produced in equal proportions?

Lodoicea maldivica (coco de mer) is a long-lived dioecious palm in which male and female plants are visually indistinguishable when immature, only becoming sexually dimorphic as adults, which in natural forest can take as much as 50 years. Most adult populations in the Seychelles exhibit biased sex ratios, but it is unknown whether this is due to different proportions of male and female plants being produced or to differential mortality. In this study, we developed sex-linked markers in Lodoicea using ddRAD sequencing, enabling us to reliably determine the gender of immature individuals. We screened 589 immature individuals to explore sex ratios across life stages in Lodoicea. The two sex-specific markers resulted in the amplification of male-specific bands (Lm123977 at 405 bp and Lm435135 at 130 bp). Our study of four sub-populations of Lodoicea on the islands of Praslin and Curieuse revealed that the two sexes were produced in approximately equal numbers, with no significant deviation from a 1:1 ratio before the adult stage. We conclude that sex in Lodoicea is genetically determined, suggesting that Lodoicea has a chromosomal sex determination system in which males are the heterogametic sex (XY) and females are homogametic (XX). We discuss the potential causes for observed biased sex ratios in adult populations, and the implications of our results for the life history, ecology and conservation management of Lodoicea.

Establishment of parallel altitudinal dines in traits of native and introduced forbs.

Due to altered ecological and evolutionary contexts, we might expect the responses of alien plants to environmental gradients, as revealed through patterns of trait variation, to differ from those of the same species in their native range. In particular, the spread of alien plant species along such gradients might be limited by their ability to establish clinal patterns of trait variation. We investigated trends in growth and reproductive traits in natural populations of eight invasive Asteraceae forbs along altitudinal gradients in their native and introduced ranges (Valais, Switzerland, and Wallowa Mountains, Oregon, USA). Plants showed similar responses to altitude in both ranges, being generally smaller and having fewer inflorescences but larger seeds at higher altitudes. However, these trends were modified by region-specific effects that were independent of species status (native or introduced), suggesting that any differential performance of alien species in the introduced range cannot be interpreted without a fully reciprocal approach to test the basis of these differences. Furthermore, we found differences in patterns of resource allocation to capitula among species in the native and the introduced areas. These suggest that the mechanisms underlying trait variation, for example, increasing seed size with altitude, might differ between ranges. The rapid establishment of clinal patterns of trait variation in the new range indicates that the need to respond to altitudinal gradients, possibly by local adaptation, has not limited the ability of these species to invade mountain regions. Studies are now needed to test the underlying mechanisms of altitudinal clines in traits of alien species.

Development of a tool for coding safety-netting behaviours in primary care: a mixed-methods study using existing UK consultation recordings.

BACKGROUND: Safety netting is recommended in a variety of clinical settings, yet there are no tools to record clinician safety-netting communication behaviours. AIM: To develop and assess the inter-rater reliability (IRR) of a coding tool designed to assess safety-netting communication behaviours in primary care consultations. DESIGN AND SETTING: A mixed-methods study using an existing dataset of video-and audio-recorded UK primary care consultations. METHOD: Key components that should be assessed in a coding tool were identified using the published literature and relevant guidelines. An iterative approach was utilised to continuously refine and generate new codes based on the application to real-life consultations. After the codebook had been generated, it was applied to 35 problems in 24 consultations independently by two coders. IRR scores were then calculated. RESULTS: The tool allows for the identification and quantification of the key elements of safety-netting advice including: who initiates the advice and at which stage of the consultation; the number of symptoms or conditions the patient is advised to look out for; what action patients should take and how urgently; as well as capturing how patients respond to such advice plus important contextual codes such as the communication of diagnostic uncertainty, the expected time course of an illness, and any follow-up plans. The final tool had substantial levels of IRR with the mean average agreement for the final tool being 88% (κ = 0.66). CONCLUSION: The authors have developed a novel tool that can reliably code the extent of clinician safety-netting communication behaviours.

Safety netting in routine primary care consultations: an observational study using video-recorded UK consultations.

BACKGROUND: Safety-netting advice is information shared with a patient or their carer designed to help them identify the need to seek further medical help if their condition fails to improve, changes, or if they have concerns about their health. AIM: To assess when and how safety-netting advice is delivered in routine GP consultations. DESIGN AND SETTING: This was an observational study using 318 recorded GP consultations with adult patients in the UK. METHOD: A safety-netting coding tool was applied to all consultations. Logistic regression for the presence or absence of safety-netting advice was compared between patient, clinician, and problem variables. RESULTS: A total of 390 episodes of safety-netting advice were observed in 205/318 (64.5%) consultations for 257/555 (46.3%) problems. Most advice was initiated by the GP (94.9%) and delivered in the treatment planning (52.1%) or closing (31.5%) consultation phases. Specific advice was delivered in almost half (47.2%) of episodes. Safety-netting advice was more likely to be present for problems that were acute (odds ratio [OR] 2.18, 95% confidence interval [CI] = 1.30 to 3.64), assessed first in the consultation (OR 2.94, 95% CI = 1.85 to 4.68) or assessed by GPs aged ≤49 years (OR 2.56, 95% CI = 1.45 to 4.51). Safety-netting advice was documented for only 109/242 (45.0%) problems. CONCLUSION: GPs appear to commonly give safety-netting advice, but the contingencies or actions required on the patient's part may not always be specific or documented. The likelihood of safety-netting advice being delivered may vary according to characteristics of the problem or the GP. How to assess safety-netting outcomes in terms of patient benefits and harms does warrant further exploration.

Phylogeography of native ploidy levels and invasive tetraploids of Solidago gigantea.

Ploidy level is an important aspect of the genetic makeup of a plant, and can strongly influence ecological characteristics such as invasiveness. We used a phylogeographical approach to elucidate the history of polyploidization and colonization success of diploid and tetraploid Solidago gigantea Aiton (Asteraceae) within its native range in North America. We were also able to identify the probable source material of the haplotype lineages invasive in Europe and Asia, where only tetraploid plants occur. To do this, we sequenced 1275 bp of chloroplast intergenic spacer DNA in 268 individuals from 57 populations. In addition, we performed a crossing experiment, which supported the hypothesis that chloroplast inheritance in this species is maternal. The phylogeographical analysis showed a complex pattern of 20 haplotypes of diploid and tetraploid plants. In North America, we found significant differentiation among regions, private haplotypes, and isolation by distance. Ploidy levels were more differentiated in the northern regions than in the South. The haplotype network was shallow and included one tetraploid-only, star-shaped cluster of haplotypes that were particularly successful colonizers. Post-glacial migration of diploid S. gigantea occurred mainly northwards east of the Appalachian Mountains, and to a lesser degree also southward. Our data suggest that tetraploids have formed several times in North America. Haplotype number and diversity were lower in European populations than in the native range, and we found evidence that four haplotypes were introduced to Europe from two source areas, New England and the Southern Appalachian Mountains.