Annals of Botany

Background and aimsThis study combines morphological and environmental data to better understand a Brunfelsia (Solanaceae) species complex, aiming to clarify patterns of variation and identify ecological factors that shape morphotype boundaries. Such an approach provides a broader perspective on how organisms respond to environmental gradients and contributes to a more comprehensive understanding of biodiversity. MethodsWe analyzed 273 herbarium specimens for 13 morphological traits using univariate and ordination analyses, namely PCA and CVA. Climatic and edaphic variables were extracted for 147 specimens with georeferenced records. To assess habitat suitability and the ecological niche of each predefined morphotype, niche models under present conditions and niche overlap tests were conducted. A redundancy analysis (RDA) was applied to evaluate how environmental predictors explain variation in vegetative and floral traits. Finally, DAPC was used to estimate membership probabilities based on morphological and environmental data. Key ResultsTwo well-differentiated groups were recovered: the capitata-hydrangeiformis morphotype, allegedly composing a cline, and the ecologically and morphologically distinct "bahia" morphotype. Variation in floral traits was better explained by environmental predictors than variation in vegetative traits; moreover, floral traits were able to delineate morphotypes more robustly when plotted in isolation. However, when analyzing the results of ecological niche overlap, a significant ecological separation of the "bahia" morphotype from the others was observed. Therefore, key morphological characters for the taxonomy of Brunfelsia covary in part with environmental variables. ConclusionsThese findings support the recognition of "bahia" morphotype as a distinct species to be formally described. This integrative approach contributes to understanding diversification processes in biodiversity hotspots and highlights hidden taxonomic diversity within Brunfelsia, where many rare and narrow-endemic taxa lie.

PremiseHerbarium specimens are increasingly used to extract morphological traits for ecological and evolutionary studies, yet the effects of tissue desiccation on trait measurements remain poorly understood. Here, we tested whether higher tissue water content leads to greater measurement changes after herborization (H1) and whether fresh trait values can be reliably predicted from herbarium measurements (H2). MethodsWe evaluated the reliability of herbarium-based measurements by comparing fresh and dried traits of leaves, flowers, fleshy fruits, and seeds across 262 individuals representing 133 Neotropical Myrtaceae species. Phylogenetic least square models and machine-learning regressions were used to test H1 and H2. ResultsLeaves and flowers generally shrank after herborization, fruits size metrics tended to increase, and seeds were largely unaffected. Water content was significantly associated with the magnitude of herborization effects in flowers and some leaf and seed traits. Fresh trait values were accurately predicted from herbarium measurements. Prediction errors were lowest for leaf traits, followed by fruits, flowers, and seeds. DiscussionThese results partially support H1 and support H2, indicating that herbarium specimens can be reliably used for trait analyses when organ-specific responses are considered, providing a practical framework to account for potential desiccation bias in functional trait research.

Lack of sexual reproduction limits the fitness and long-term viability of many plant populations. This may pose a particular problem for populations at the edges of species ranges, which are often small and isolated and therefore may be less likely to attract pollinators. But despite the fact that many range-edge populations are of significant conservation concern and value, there is often little information about which visitors are effective pollinators, and few explicit tests of whether range-edge populations experience reduced pollination. Here, we assess which visitors are effective pollinators of sundial lupine (Lupinus perennis), a legume that is threatened in much of its range, and whether pollination success varies between populations in the range core and those at the species northern range edge. Across six populations in the northern USA and southern Canada (Ontario), sundial lupine was visited almost exclusively by bees, but only large bees (Bombus, Xylocopa) could be confirmed as effective pollinators in single-visit experiments. While seed production varied significantly among populations, visitation rates did not. Neither pollinator visitation, pollen receipt, nor seed production declined at sundial lupines northern range edge. We therefore found no evidence that pollination success constrains either performance of at-risk populations of sundial lupine or the species northern range limit.

Understanding evolutionary relationships in hyperdiverse plant groups remains a major challenge in systematics. The orchid genus Bulbophyllum, the second largest genus of flowering plants, represents an exceptional example of phylogenetic and morphological complexity. Relationships, particularly within the species-rich Asian clade, have remained poorly resolved due to extensive morphological variation and limited resolution in previous phylogenetic studies. Here, we reconstructed phylogenetic relationships using 63 plastid genes from 355 specimens representing 322 species and 65 of the 97 recognised sections of Bulbophyllum. Our analyses confirmed that the genus comprises five major evolutionary lineages comprised of species predominantly from Australasia, Madagascar, Continental Africa, Neotropics, and Asia. We provide the first robust phylogenetic evidence for a dichotomous split within the Asian clade into two well-supported lineages: the Asian-Malesian clade and the Malesian-Papuasian clade, with the latter containing a strongly supported Papuasian subclade. Additionally, this study supports the monophyly of several currently recognised sections while clarifying relationships in previously problematic groups. This study provides the most comprehensive plastid-based phylogenomic framework for Bulbophyllum to date and establishes a foundation for future taxonomic revision and integrative analyses of diversification and trait evolution within this hyperdiverse genus.

BackgroundPlants are exposed to various environmental challenges. With ongoing climate change, droughts and insect outbreaks are expected to become more frequent. Thus, a better understanding is needed of how different plant species respond to such single and combined challenges. This study investigated common versus species-specific responses to environmental challenges in three perennial plant species of different growth forms and whether responses differ intraspecifically among accessions. Clones of different accessions of the herbaceous species Tanacetum vulgare, the woody vine Solanum dulcamara, and the tree Populus nigra were subjected to similar control, herbivory, drought, and combined (drought and herbivory) treatments for the same periods. After the exposure, concentrations of foliar phytohormones and various morphological traits were measured. ResultsAcross all species, several foliar phytohormones and one of ten morphological traits responded consistently to the environmental challenges. Jasmonoyl-isoleucine was induced by herbivory and the combined treatment, abscisic acid (ABA) by drought and the combined treatment, and indole acetic acid by the combined treatment in all species. Root mass remained unchanged in all species. However, structural equation models (SEMs) revealed a shared regulatory pathway across species in which ABA connected treatment and root mass, indicating a common hormonal response potentially linking challenges to growth responses. Despite these common patterns, species-specific responses were pronounced. In P. nigra, a unique induction of salicylic acid was found under the combined treatment, while aboveground mass and root-shoot ratio remained unaffected by any treatment, in contrast to the other two species. Species-specific SEMs further indicated distinct phytohormone-mediated pathways underlying morphological variation. Phenotypic plasticity reflected these species-specific patterns, with none of the phytohormones or morphological traits exhibiting uniform plasticity across species. Intraspecific variation further shaped responses, as phytohormone and morphological trait plasticity depended on accession, indicating substantial accession-specific plant responses. ConclusionsOur results indicate that some responses to comparable challenges may be conserved across species, while others are species-specific. The combined treatment elicited the most pronounced responses, and such complex responses may become more frequent under current global change. Our study highlights that comprehensive understanding of plant responses requires systematic comparisons at both interspecific and intraspecific scales.

Background and AimsComplex genomic histories driven by hybridization and polyploidy can shape key plant traits such as defense, stress tolerance, and toxicity, particularly in Amaran-thaceae, which includes crops such as quinoa and spinach. Within this family, white goosefoot (Chenopodium album) is both a widespread agricultural weed and a traditional food resource. However, its evolutionary history is complicated by discordant signals among genomic markers within the C. album complex, comprising diploid, tetraploid, and hexaploid taxa. Here, we tested whether reticulate evolution underlies this genome-wide discordance. MethodsUsing genome-scale phylogenomic data, we analysed 2,298 conserved nuclear loci (BUSCO genes) across 27 Amaranthaceae genomes. Both single- and multicopy gene families were included to capture signals of gene duplication, incomplete lineage sorting, and hybridization. Complementary phylogenomic approaches were used to evaluate whether the evolutionary history is best supported by strictly bifurcating relationships or by reticulate evolution. Key ResultsA consistent C. album lineage was recovered, comprising tetraploid and hexaploid C. album cytotypes together with C. suecicum, C. strictum, C. formosanum, C. acuminatum, and C. opulifolium. Phylogenetic discordance was concentrated within Chenopodium, particularly around the C. album and C. quinoa lineages. Models incorporating hybridization fit better than strictly bifurcating relationships, supporting at least two reticulation events. Hybridization signals were detected in 271 loci in tetraploid and 270 in hexaploid C. album, of which 232 were shared, indicating a shared hybrid origin rather than independent lineages. ConclusionsThe evolutionary history of the C. album lineage is best explained by reticulate processes involving hybridization and polyploidy. Conserved nuclear loci retain persistent signatures of these events, helping to resolve complex evolutionary histories in polyploid plant systems.

Premise of studyUnder increasingly frequent pollinator-limited environments, plants need to rely on modes of reproductive assurance such as selfing and cloning. However, few studies investigate the interplay between selfing and cloning in plants that can do both. Here, we explore mechanisms determining the relative expression of selfing and cloning throughout the European distribution of the wild woodland strawberry (Fragaria vesca) under a pollinator-free environment. MethodsWe established an outdoor common garden with 121 woodland strawberry genotypes from across Europe and excluded them from pollinators. For each genotype, we recorded reproductive traits and performed hand-pollination treatments. Key ResultsWe found a weak trade-off between cloning and selfing, driven by increased seed and fruit provisioning rather than flower production. The capacity to autonomously self-fertilize was determined by the lateral proximity of the anthers to the pistils (lateral herkogamy), but not by early inbreeding depression. Genotypes sampled at lower latitudes and altitudes were better at self-fertilizing and had smaller petals. The propensity to clone increased towards the east, where genotypes also had smaller petals, particularly at higher latitudes. ConclusionAt the species level, we detected a trade-off between the propensity for clonal reproduction and the capacity for self-fertilization. At a continental scale, the capacity to self-fertilize varied along a north-south gradient, whereas clonal propensity varied along an east-west gradient. Our results suggest that these two modes of reproductive assurance may compensate for reduced pollinator attractiveness (smaller petals) in regions where each mode is most strongly expressed.

Reduced competition or facilitation between kin relative to nonkin can improve plant performance, particularly under resource-limited conditions. Understanding whether kin interactions differ between invasive and native species may provide insights into the mechanisms underlying the persistence and spread of invasive species, particularly for species that spread clonally. To explore this, we conducted a greenhouse experiment using the invasive Alternanthera philoxeroides and its native congener A. sessilis in China. For both species, we grew central plants without or with neighbors, and for the latter we had three intraspecific neighbor kinship treatments (kin only, nonkin only, and both kin and nonkin [mixed] neighbors). To test whether kinship effects are affected by resource limitation, we grew the plants under two watering conditions (well-watered and drought-stressed). Our findings revealed that at both the group (i.e., pot-level) and individual levels, invasive plants had a higher biomass production and experienced a less negative relative neighbor effect in kin groups than in nonkin groups, while these patterns were reversed in the native species. Although aboveground architecture of central plants did not differ significantly between kin and nonkin neighbors in either species, neighbor plants of the invasive species produced fewer nodes in kin groups than in nonkin groups, while the reverse was true for the native species. These patterns were not affected by the watering treatment. Together, these results indicate that while the native plants has stronger kin competition, the invasive species has reduced kin competition. Such reduced competition among kin in the invasive Alternanthera philoxeroides may enhance its population dominance and facilitate its spread.

O_LIQuantifying relationships between traits and climate using plants collected from diverse climatic origins, grown under common conditions, potentially provides valuable insights into climate adaptation. C_LIO_LIWe report on fifteen accessions of kangaroo grass (Themeda triandra), a C4 species distributed across Australia, Asia, the Middle East and Africa from the Andropogoneae clade of grasses that is vital to global agriculture. Plants were grown to maturity in glasshouses under two thermal regimes, with ample water supplied. Numerous physiological, "economic" and developmental traits were characterised. C_LIO_LIAs expected, plants grown at 20{degrees}C maxima had lower photosynthetic rates (Asat) and dark respiration rates, reduced leaf expansion, and delayed flowering compared with plants grown at 30{degrees}C. However, surprisingly few traits varied with climate-of-origin: accessions from colder climates had higher Asat alongside lower leaf mass per area, but only when grown at 20{degrees}C; flowering time showed the strongest correlation with site climate, with plants from wetter, warmer or less variable climates taking longer to flower. C_LIO_LIOur findings highlight remarkable phenotypic flexibility in key traits of T. triandra; this flexibility is likely key to its wide distribution. The strong relationship between flowering time and climate-of-origin underscores the importance of reproductive phenology as an adaptive trait. C_LI

Polyploidy is often thought to cause immediate reproductive isolation due to sterility and inviability of inter-ploidy offspring. However, recent research demonstrated genome-wide introgression in natural populations of diploids and tetraploids. Yet, it still remains unknown whether introgression varies in strength along the genome and what are the forces underlying such variation. Here we analyzed whole-genome resequencing data from natural populations of the Alder tree, Alnus glutinosa agg., which includes a widespread diploid lineage found across large parts of Europe and two autotetraploid lineages with more limited ranges on the Balkan and Iberian Peninsulas. Our sampling involved mixed-ploidy populations, where diploids, triploids and tetraploids co-occur as well as ploidy pure populations. We identified genomic regions of increased admixture, which coincide with putative locations of centromeres. We hypothesize that this pattern of shared variation at pericentromeric regions involves centromere drive, which happens when centromeres increase the likelihood of being included in the oocyte during female meiosis and which has been studied in only a few plant species. While it was previously suggested that centromere drive could cause reproductive isolation and speciation, here we propose that driving centromeres could be able to lift reproductive barriers caused by ploidy differences.

Long-term field observations typically are the "gold-standard" for inferences of phenological sensitivities in montane systems but are spatially limited. Herbarium specimens provide broader spatial coverage, but their utility to accurately capture montane phenology remains poorly known. We compared flowering phenology of 45 species inferred from herbarium specimens with comparable data from nearly 50 years of direct observations at the Rocky Mountain Biological Laboratory. Estimates of flowering time and phenological sensitivity to snow density were consistent between herbarium specimens and observations, but observations revealed secondary flowering peaks. Herbarium specimens additionally yielded shallower estimates of phenological sensitivity to spring temperature than did field observations. Across co-occurring species, "early" flowering individuals inferred from herbarium specimens, rather than the mean response across all individuals, may better approximate community-level phenological responses to temperature changes. We conclude that herbarium specimens are reliable resources for closing gaps in understanding phenological variation along elevational gradients of montane systems.

Background and AimsNon-native species are now ubiquitous members of regional floras. The factors that lead to establishment and dominance of non-native species are continuously debated. Fundamental hypotheses about drivers of invasion success include the role of phylogeny, polyploidy, genome size, and rapid niche evolution. These hypotheses have been tested in the seed plants, but ferns, the second largest group of vascular plants, have rarely been considered in these analyses, despite making up a non-trivial portion of non-native floras. MethodsWe compiled a dataset of global non-native ferns and categorized them along the invasion spectrum using descriptions from the literature and natural history collections. Using this dataset, we assessed I) the taxonomic diversity and phylogenetic clustering of non-native ferns, II) the geographic distribution of fern introductions, testing for shifts in climatic niches, and III) test for the association of invader traits across the invasion continuum, including smaller genome sizes and higher ploidal levels. Key ResultsWe generated a dataset that includes 83 taxa; of these, we classified 18 as casual, 35 as naturalized (but not invasive), and 30 as invasive. Using this dataset, we found I) weak or no phylogenetic clustering of non-native ferns, II) some regions are overrepresented as sources and recipients of introductions, III) climatic niches are often conserved between native and introduced ranges, but can differ between introductions, IV) naturalized ferns have smaller genomes, and V) invaders have higher ploidal levels. ConclusionsWe integrated regional floras, occurrence and climate data, phylogeny, and cytology to test fundamental hypotheses regarding the colonization success of ferns. This study provides insights into the ecological, genomic, and phylogenetic features associated with the colonization of new habitats by non-native ferns, a largely overlooked portion of non-native plant taxa.

O_LIIn fluctuating environments, the kinetics of stomatal opening and closing influence the balance between carbon gain and water loss. Smaller guard cells may respond faster to fluctuating environmental conditions because of their greater surface area for osmolyte flux relative to cell volume. A related hypothesis is that operational stomatal conductance (gop) is often well below its theoretical maximum (gmax) because at this stomatal aperture, guard cell volume is poised to change rapidly with small changes in turgor pressure. C_LIO_LIWe analyzed 2,124 estimates of stomatal closure kinetics in response to an abrupt increase in vapor pressure deficit (VPD) among 29 diverse wild tomato populations in the genus Solanum. C_LIO_LILeaves with small guard cells and a lower gop to gmax ratio (fgmax) closed faster, but explained variation in kinetic parameters at different levels of biological organization. Guard cell size had high phylogenetic heritability and varied relatively little within populations, whereas fgmax varied mostly among individuals and between light intensity treatments. C_LIO_LISmaller stomata can be speedier, but only if stomata are held at an aperture where they are responsive to changing turgor pressure. Selection on stomatal speed may influence not only anatomical traits like guard cell size, but also physiological controls on gop. C_LI

Polyploidization is widely recognised as a major driver of plant diversification, with many species persisting as mixed-ploidy systems where multiple cytotypes co-exist. Polyploids are disproportionately represented among invasive species, yet their role in facilitating biological invasions remains poorly understood. Lantana camara, one of the worlds most successful invasive plants, exhibits remarkable cytotype diversity, but the distribution and evolutionary relationships of these cytotypes in its native and invasive ranges have remained unclear. Here, we characterise ploidy variation and assess genetic differentiation among cytotypes in invasive L. camara populations across India. Flow cytometry of more than a thousand individuals reveals that tetraploids overwhelmingly dominate the invasive range, accounting for more than 95% of individuals, while triploids and hexaploids occur at much lower frequencies. Using genome-wide ddRAD-derived SNP markers from diploids, triploids, tetraploids, and hexaploids, we find no genetic differentiation among cytotypes. Instead, individuals of different ploidy levels cluster together across multiple genetic clusters, consistent with recurrent and potentially independent origins of polyploids. These patterns further suggest that L. camara polyploids likely arise via autopolyploid formation. Together, our results establish tetraploidy as the predominant cytotype in Indias invasive populations and reveal a lack of cytotype-specific genetic structure. These findings highlight the need to investigate the ecological advantages of tetraploids and the mechanisms that generate cytotype diversity, key steps toward understanding how polyploidy contributes to the invasive success of this globally important species.

Belowground, plants are exposed to a wide range of biotic stresses that vary in severity and nature, including tissue damage, disruption of vascular connectivity, and depletion of assimilates. How plants adapt their root systems to cope with different types of belowground biotic stresses is not well known. In this paper we compare above- and belowground plant adaptations to three nematode species with distinct tissue migration and feeding behaviours to study mechanisms underlying tolerance to different types of biotic stresses. We monitored both green canopy growth and changes in root system architecture of Arabidopsis inoculated with Pratylenchus penetrans, Heterodera schachtii, and Meloidogyne incognita. This revealed three distinct phases in aboveground plant responses: (i) initial growth inhibition associated with host invasion and tissue damage, (ii) persistent growth reduction associated with nematode sedentarism, and (iii) late growth stimulus in more advanced stages of infection. Specific adaptations in the root systems further revealed fundamentally different stress coping strategies. Tissue damage and intermittent feeding by P. penetrans in the root cortex did not induce significant changes in root system architecture. Tissue damage to the root cortex and prolonged feeding on host vascular cells by H. schachtii induced secondary root formation compensating for primary root growth inhibition. Prolonged feeding on host vascular cell by M. incognita alone did not induce secondary root formation, but was accompanied by typical local tissue swelling instead. Our data suggest that local secondary root formation and tissue swelling are two distinct compensatory mechanisms underlying tolerance to sedentarism by root-feeding nematodes. HighlightHow plants utilize root system plasticity to cope with different types of biotic stresses by root feeding nematodes remains largely unknown. Here, we report on specific adaptive growth responses in Arabidopsis roots to three nematode species, Pratylenchus penetrans, Heterodera schachtii, and Meloidogyne incognita, with fundamentally different strategies for host invasion, subsequent migration through host tissue, and feeding on host cells.

Montane plant populations are experiencing novel conditions due to climate change. Furthermore, climate change is causing increased climate perturbations, such as the 2012-2016 drought in the western US, remarkable in its aridity, longevity, and warmer temperatures. This drought provided an opportunity to understand how montane populations respond to extreme perturbations, including at range limits. We resurrected seeds of the endemic annual plant Erythranthe laciniata, collected in 2008 or earlier (before the drought) and in 2014 (the height of the drought), in a common garden experiment to understand how drought influenced evolution in contemporary field conditions. The study included nine populations across the species range, including range edges. Over 2,100 replicates were sown in three common gardens at natural populations at low, central, and high elevations. We recorded phenology and flower production to estimate lifetime fitness. This experiment took place in 2021, a year with low precipitation and high temperatures. We found higher fitness in the drought generation at the high garden, while both generations showed similar fitness at the central and low gardens. We detected climate adaptation at the low and high gardens, and rapidly evolved faster phenology at the high garden. Lifetime fitness was substantially lower at lower gardens overall, even for low-elevation populations. Low-elevation populations outperformed central populations at the central garden, suggesting adaptive mismatch. Together, these results indicate rapid contemporary adaptation that is beneficial at the leading edge of the species range. Nevertheless, low fitness at lower elevations may foreshadow range contraction under continued climate change.

O_LIPlants take up nutrients from the soil while investing in absorptive root surface or mycorrhizal partners. Root hairs - a major structure for nutrient uptake and cheap to build - increase the absorptive root surface. As such they are an important component of plant resource economics but largely neglected in root economic concepts so far. C_LIO_LIThis is mainly due to data scarcity, which we set out to overcome by measuring root-hair traits on 82 European grassland species in a greenhouse experiment. Using fluorescence and light microscopy, root-hair length and incidence was measured along with mycorrhizal colonization. C_LIO_LIWe found a phylogenetically conserved trade-off between plant investment into root hairs and mycorrhiza. A similar trade-off between root-hair incidence and mycorrhiza occurred at the intraspecific level, while patterns were heterogeneous among species. Plant species with high colonization rates showed the highest variability in root-hair incidence. C_LIO_LIWe conclude that plants vary along a gradient ranging from investment into root hairs as part of a "do-it-yourself" strategy to collaboration with mycorrhizal fungi while showing intraspecific variation in root-hair incidence. These findings demonstrate that root hairs play a fundamental role in fine-root trait variation and need to be considered when studying belowground plant economic strategies. C_LI

Timing of flowering is shifting with climate change. Although climate-driven shifts in phenology sometimes affect seed production, whether changing phenology will scale up to affect population dynamics of long-lived plants remains largely unknown, particularly under changing precipitation. Understanding how phenology affects persistence and extinction risk is a pressing need given contemporary biodiversity loss. We combined nearly a decade of demographic censuses and a four-year phenological survey in a rainfall manipulation experiment to examine the effects of experimental drought and irrigation on flowering phenology, vital rates (e.g., survival and individual growth), and population growth in the perennial herb Lomatium utriculatum. We found that drought advanced flowering by 3.3 days on average, and that earlier-flowering plants produced more seeds regardless of treatment. However, both rainfall treatments reduced seed production compared to controls. We quantified the phenology-mediated and direct, non-phenological effects of rainfall manipulation on population growth rates using integral projection models and a life table response experiment. Drought and irrigation increased {lambda} through increased individual growth, but these effects were partially negated by treatment-driven declines in seed output. In contrast, changes to seed production resulting from shifting flowering times had negligible effects on population growth. Our results suggest that climate-driven phenological shifts may only marginally impact population dynamics in perennial plants and highlight that assessing phenologys consequences for persistence under climate change must also account for direct demographic effects of the climate driver(s) themselves. SignificanceWill changing flowering times under climate change increase extinction risk in plant populations? Despite well-documented earlier flowering and its influence on the number of offspring produced, how changing flowering times will affect population growth or decline is still mostly unknown. We study this in a perennial wildflower subject to changes in rainfall. While we found that drought meant earlier flowering and that, all else equal, early flowering meant more seeds, these effects only marginally affected population growth. Instead, population growth was influenced mostly by rainfall-driven changes to individual plant growth. While shifting flowering times remain an important indicator of climate change, assessing extirpation in plants requires considering flowering times as only one of many life cycle processes changing with climate.

The ecological and evolutionary processes determining species range limits remain poorly understood. Ultimately, range limits depend on the species abilities to persist under heterogeneous conditions, by adaptive differentiation and phenotypic plasticity, including transgenerational effects. To investigate ecological differentiation and transgenerational effects in the clonal invasive knotweed, Reynoutria japonica, in Europe, we conducted a two-phase transplant experiment: plants sampled along the entire latitudinal gradient were planted in three sites located at the northern range margin, mid-range and near the southern range margin, and then re-transplanted among all three sites after two years. Biomass production and allocation were generally not associated with latitude of origin and previous growth at the same site did not promote performance. We therefore find no evidence that adaptive differentiation or transgenerational effects contribute to the wide distribution of R. japonica in Europe. However, at the northern site, with a 25% shorter season, knotweed plants invested much less biomass below-ground, and the pattern was further strengthened in plants that had grown in the northern site in the previous generation. Overwintering below-ground rhizomes are essential for survival and spread. We further explored limiting climate conditions in a species distribution model for the European range and found that mean annual temperature and temperature annual range are the main predictors of the European distribution of R. japonica. Taken together, our study suggests that low temperatures and associated short seasons may pose a limit to the broad environmental tolerance of R. japonica and restrict its northward spread by reducing below-ground biomass accumulation.

Increasing global temperatures and the rising frequency of heat waves pose a significant threat to plant reproduction. The reproductive phase is particularly sensitive to heat stress, yet the underlying mechanisms regulating thermotolerance during this stage remain insufficiently understood, despite significant advcances in its understanding during vegetative growth. Heat stress responses are largely controlled by heat shock factors (HSFs) and their downstream targets, including heat shock proteins (HSPs). Among these, HSP101 is essential for acquired thermotolerance and recovery from stress, while HEAT SHOCK BINDING PROTEIN (HSBP) acts as a negative regulator of HSF activity, modulating the heat shock response. Here, we investigated the impact of elevated temperature regimes on the reproductive development of Arabidopsis thaliana, with a particular focus on pollen development and fertility. Our results show that heat stress negatively affects pollen development in a dose-dependent manner, leading to reduced reproductive success. We confirmed the critical role of HSP101 in reproductive thermotolerance using the hot1-3 mutant, deficient in HSP101. Furthermore, we provide evidence that the hot1-3 mutant is tetraploid. The origin of this event is unknown, but it is tempting to speculate that disruption of heat stress responses and interference with meiotic processes may lead to whole genome duplication. Overall, this study provides new insights into the regulation of plant reproductive development under heat stress and highlights the importance of HSP101 in maintaining fertility. These findings contribute to a better understanding of plant responses to rising temperatures and may inform strategies to enhance crop resilience under climate change. Main ConclusionFlowering Arabidopsis plants adapt to long-term high temperature by shortening the flowering period and reducing their fertility. The study also demonstrated that the commonly used hot1-3 mutant is tetraploid.