Post-fire regeneration characterizes woody vegetation of the Cerrado. Several species (e.g., from the Fabaceae) can resprout after fire due to the presence of storage bud-bearing belowground structures, such as xylopodia, having the capacity to rapidly allocate resources for the formation of new aboveground shoots, an advantage in fire-prone ecosystems. Therefore, we evaluated the morphoanatomical structure of the belowground organs, buds and their storage to elucidate fire-related functional traits in relation to regeneration. Besides the strong capacity of plants with xylopodia to resprout and/or their associated root suckers to propagate laterally, they also provide protection against pathogens, through the presence of defence compounds. We evaluated the morphoanatomy and performed histochemical tests with the belowground organs of eight legume species collected in open savannas in Central Brazil. Two species presented a taproot tuber and the six remaining species had a xylopodium as belowground organ. All xylopodia had buds on their upper portion. These organs were basically composed of lignified tissue, containing defence (phenolic compounds and lipidic substances), and storage (starch) substances. All xylopodia were associated to tuberous roots, and in two species these roots were also root suckers. Thus, the presence of belowground storage organs, in combination with stored defence compounds, likely facilitates the persistence of the investigated legumes in fire-prone ecosystems.

Flowering plants are essentially sessile organisms that disperse their genes through pollination, expanding their areas of occurrence through seed dispersal. In orchids, seed dispersal is commonly mediated by air currents. Conversely, members of several genera have evolved seeds adapted to endozoochory. This is the case for Vanilla, the most economically important genus in the orchid family. The role of indehiscent fruits in the attraction and rewarding of Vanilla seed dispersers was investigated based on field observations, analysis of fragrances, reward substances, and investigation of seed viability through the digestive tract. Indehiscent Vanilla fruits are consumed exclusively by herbivores, i.e. agoutis. Besides providing nutritional rewards, the fruits are rich in polyphenols that are unpalatable to omnivores. The most dominant compound in fruits is attractive only to agoutis. This is the first study showing synzoochory in Orchidaceae and specificity of seed dispersal in orchids. Indehiscent fruits may have evolved early in Neotropical Vanilla in response to selection pressures mediated by large herbivores as the genus emerged ca. 34 Mya in South America, concomitantly with megafauna diversification in the Oligocene. Extinction of the megafauna during the Pleistocene has left agoutis as inheritors of seed dispersal in species with large fleshy fruits. Apart from the effects on omnivores, this study shows that indehiscent fruits of V. chamissonis are consumed exclusively by agoutis, providing the first evidence of target mutualism in orchid seed dispersal.

Male and female dioecious plants often show sexual dimorphism, differing in morphological, physiological and life-history traits. Most previous studies have focused on differences between males and females during or after reproduction, paying little attention to the pre-reproductive stages of the individuals. Here we assessed the response of male and female individuals of the dioecious plant Silene latifolia to abiotic stress at different life stages, including pre-reproductive (i.e. seedlings and young plants) and reproductive individuals. We measured growth, resource allocation and discrimination against C under nutrient deficiency, water stress, as well as their interaction. We observed sexual dimorphism in root growth, with female seedlings having longer main roots than male plants. Pre-reproductive male and female plants also responded differently, in terms of root allocation, to nutrient and water availability. At reproduction, females grew more roots than males when water was not limiting. These differences could help explain the female-skewed sex ratios found in natural populations of S. latifolia. We found no evidence of sexual dimorphism in aboveground dry mass, although females had longer leaves than males at the seedling stage. We conclude that sexual dimorphism in S. latifolia may occur not as a consequence of reproduction, but well before it.

The orchid family is renowned for its enormous diversity in pollination biology. Many orchid species use deception to attract pollinators, and the main strategy in terrestrial orchids is food deception. Food-deceptive orchids usually show a low number of pollinator visitations, making field observations of pollinators difficult. In this study visual census, pollinator capture and molecular analysis of pollinaria found on caught insects allowed us to obtain information on species composition of orchid pollinators. A total of 321 insects were caught; most specimens were hymenopterans (Apis mellifera, Bombus ruderatus and Eucera rufa) and coleopterans (Tropinota hirta and T. squalida). The identity of species to which pollinaria found on the insect's body belonged was confirmed by molecular analysis. Moreover, some individuals of Billaea lata (Tachinidae, Diptera) were captured and photographed with the pollinaria on their head. Two new and important results emerged clearly in this work: a dipteran, Billaea lata, pollinator of Anacamptis pyramidalis, and two beetles in the genus Tropinota are pollinators of Orchis italica. Our results confirm that generalized food-deceptive orchids of the genera Orchis and Anacamptis show weak pollinator specificity.

Dittrichia viscosa (L.) Greuter, a perennial plant in the Asteraceae, has strong allelopathic activity due to the high content of various secondary metabolites. The bicyclic sesquiterpenoid α-costic acid is the most abundant secondary metabolite of D. viscosa. Its remarkable insecticidal, antiparasitic, and phytotoxic activities point to its potential use as a natural herbicide, but information on its mode of action is lacking. To shed light on the mechanism of action of α-costic acid in plant cells, we investigated the phytotoxicity of α-costic acid in tomato plants (Solanum lycopersicum L.) through in vivo assays, the underlying cellular effects using biochemical assays, and the effect on subcellular organelles using confocal microscopy on tomato protoplasts incubated with organelle-specific fluorescent probes. In vivo tests showed that α-costic acid inhibited the growth of tomato seedlings and induced chlorosis and spot lesions in leaves. Biochemical assays demonstrated that α-costic acid caused ion leakage, chlorophyll depletion, HO overproduction, callose deposition, and membrane lipid peroxidation. Confocal microscopy demonstrated that α-costic acid determined ROS overproduction and network disruption in mitochondria, singlet oxygen overproduction in chloroplasts, vacuole disintegration, and autophagosome formation. Overall, our data are consistent with a model according to which α-costic acid phytotoxicity is related to oxidative stress in mitochondria and chloroplasts that induces extensive membrane damage, ultimately resulting in cell death associated with autophagy.

Chronic reductions in soil moisture combined with high air temperatures can modify tree carbon and water relations. However, little is known about how trees acclimate their foliar structure to the individual and combined effects of these two climate drivers. We used open-top chambers to determine the multi-year effects of chronic air warming (+5 °C) and soil moisture reduction (-50%) alone and in combination on the foliar anatomy of two European tree species. We further investigated how these climate drivers affected the relationship between foliar anatomy and physiology/chemistry in young downy oak and European beech trees. After 4 years, reduced soil moisture led to development of thinner leaves with a narrower epidermis and lower gas exchange for oak and beech, but to a lesser extent in the latter. In contrast, prolonged warming did not affect the anatomical and physiological/chemical traits in either species. Warming also did not exacerbate the impacts of dry soils, highlighting soil moisture as the key driver in leaf anatomical shifts. While soil moisture altered oak foliar anatomy, and the physiology and chemistry of both species, our work revealed a limited acclimation potential towards more drought- and heat-tolerant leaves as conditions become drier and warmer, suggesting potentially high vulnerability of both species to future climate predictions.

Ceratostigma willmottianum Stapf is a unique chalk gland (salt-excreting) plant from China, with a salt gland structure that excretes white crystals of calcium carbonate (CaCO), which has potential biomineralization and carbon sequestration functions. Due to the narrow distribution of wild germplasm resources, there is a lack of diversity of new varieties to satisfy commercial development and scientific exploration. Therefore, we used ethyl methanesulfonate (EMS) mutagenesis to obtain new dwarf mutant germplasm, and analysed it in terms of morphology, growth, photosynthesis, salt glands, and excretion traits. All four dwarfing mutant strains (DM1, DM2, DM3, and DM4) exhibited extreme dwarfing (62.28%, 62.28%, 74.55% and 61.68% reduction in plant height, respectively), faster growth, increased belowground root biomass, and earlier bud differentiation and flowering. Photosynthetic capacity was enhanced: chlorophyll content, maximum quantum yield of PSII (Fv/Fm), effective quantum yield of PSII (ΦPSII), photochemical quenching coefficient (qP), electron transfer rate (ETR), net photosynthesis (Pn), intercellular CO concentration (Ci), stomatal conductance (Gs), and transpiration (Tr), were significantly higher in leaves of DM mutants. The density of salt glands per unit leaf area and average Ca excretion rate of individual salt glands increased significantly (especially in DM2), and CaCO accumulation per unit leaf area was 28.57% higher than that of the wild type. Pearson correlation analysis showed that photosynthetic capacity was significantly and positively correlated with CaCO excretion. The above study not only provided enriched new germplasm of C. willmottianum, but also important research material for studying the mechanism of CaCO excretion by salt glands and carbon sequestration capacity of biomineralization.

Stilbenes, naturally occurring polyphenolic secondary metabolites, play a pivotal role in adaptation of various plant species to biotic and abiotic factors. Recently, increased attention has been directed toward their potential to enhance plant stress tolerance. We evaluated drought tolerance of three grapevine varieties grown with different levels of water deficit. Throughout, we studied physiological mechanisms associated with drought stress tolerance, particularly stilbene accumulation in root tissues, using HPLC. Additionally, we explored the possible relationship between antioxidant potential and stilbene accumulation in response to water deficit. The results underscore the detrimental impact of water deficit on grapevine growth, water status, and membrane stability index, while revealing varying tolerance among the studied genotypes. Notably, Syrah variety had superior drought tolerance, compared to Razegui and Muscat d'Italie grapes. Under severe water deficit, Syrah exhibited a substantial increase in levels of stilbenic compounds, such as t-resveratrol, t-piceatannol, t-ɛ-viniferin, and t-piceid, in root tissues compared to other genotypes. This increase was positively correlated with total antioxidant activity (TAA), emphasizing the active role of resveratrol and its derivatives in total antioxidant potential. This demonstratres the potential involvement of resveratrol and its derivatives in enhancing antioxidant status of the drought-tolerant Syrah grape variety. Our findings suggest that these stilbenes may function as valuable markers in grapevine breeding programs, offering novel insights for the sustainable cultivation of grapevines in water-limited environments.

The root system harbours complex bacterial communities, which are critical for plant growth and health. Significant differences exist between bacterial communities in the root compartments; however, limited reports have explored their phylogenetic composition and niche conservatism in the root system of sorghum. We used the sorghum Hongyingzi cultivar as test plant, and applied 16S rRNA high-throughput sequencing and various statistical approaches. Phylogenetic composition of bacterial communities in root compartments were primarily driven by closely related species with similar environmental adaptations. We also found evidence of phylogenetic niche conservatism in bacterial communities for edaphic factors in the various root compartments, with pH and available N playing essential roles in shaping community composition. Environmental threshold analysis revealed threshold ranges of dominant taxa for pH and available N, indicating wider adaptive thresholds for more abundant taxa. Reconstruction of ancestral states suggested evolutionary changes in adaptability of certain bacterial taxa to edaphic factors, suggesting a shift towards slightly acidic, high N environments and reflecting the prolonged mutual interaction between bacteria and plants in cultivated soils. These findings enhance our understanding of environmental responses and evolutionary dynamics of root-associated microbiota in young sorghum plants and provide novel insights into ecological adaptations, shedding light on their responses to environmental factors. Our study contributes to a better understanding of the ecological dynamics of root-associated microbiota and offers analytical pathways for exploring the nutritional regulation of root microbiota.

A fundamental goal in ecology and evolution is to explain the factors that shape species' abundance and range limits. Evaluating the performance of early life-stages across an altitudinal gradient can be valuable for understanding what factors shape range limits and for predicting how plant species may respond to climate change. To experimentally evaluate the presence of local adaptation in a threatened palm (Euterpe edulis) at early life-stages, we reciprocally sowed seeds at two contrasting elevations. In addition, to evaluate the effect of seed predation on E. edulis seed germination and seedling establishment, seed addition experiments were conducted at three different elevations. Our results showed no evidence of local adaptation in the early life-stages for the two E. edulis populations. We observed lower germination and seedling performance of both E. edulis populations at the low-elevation site. The exclusion of seed predation increased seedling establishment across all elevations. Seed predation and dry soil conditions were the main factors that constrained seedling establishment at the upper altitudinal limit and at the lower elevation, respectively. Climate change in the study area will result in warmer and drier environmental conditions. The lack of local adaptation and the lower performance of both E. edulis populations in warm and dry conditions, combined with a higher seed predation at the upper altitudinal limit, might cause an altitudinal range contraction, increasing the vulnerability of this threatened species to climate change.

Angiosperm pollen, the male gametophyte, plays a crucial role in facilitating fertilization by protecting and transporting male sperm cells to the female pistil. Despite their seemingly simple structure, pollen grains undergo intricate development to produce viable sperm cells capable of fertilizing the egg cell. Factors such as resource limitation and plant aging can disrupt normal pollen development and affect pollen performance. We investigated the influence of plant resources and aging on pollen developmental failure in Azorella nivalis Phil., an exceptionally long-lived high-Andean species that grows in a stressful alpine environment. Leveraging the modular nature of plants, we aimed to identify intra-individual sources of variation in pollen developmental failure. By using pollen viability and variation in viable pollen grain size as indicators of pollen developmental performance, we assessed whether proxies of plant resource availability and aging influenced these pollen traits at the inter-individual, inter-flower and intra-flower levels. Our findings revealed decreased pollen viability in putative resource-depleted flowers and in shoots that experienced higher levels of meristematic divisions from the zygote (i.e., greater cell depth). Additionally, we observed increased variability in the size of viable pollen grains in resource-depleted anthers. Our study suggests that resource availability and shoot aging are critical determinants shaping pollen development in long-lived plants at the intra-individual level. These findings contribute to our understanding of how differences in male fitness can arise in plants, with implications for their evolutionary trajectory.

Cadmium (Cd) is an abiotic stressor negatively affecting plant growth and reducing crop productivity. The effects of Cd (25 μM) and of pre-soaking seeds with salicylic acid (SA) (500 μM) on morphological, physiological, and glycerolipid changes in two cultivars of wheat (Triticum aestivum L. 'Tosunbey' and 'Cumhuriyet') were explored. Parameters measured were length, fresh and dry biomass, Cd concentration, osmotic potential (ψ), lipid peroxidation, and polar lipid species in roots and leaves, as well as leaf chlorophyll a, carotenoids, and fv/fm. Fresh biomass of roots and leaves and leaf length were strongly depressed by Cd treatment compared to the control, but significantly increased with SA + Cd compared to Cd alone. Cd reduced leaf levels of chlorophyll a, carotenoids, and fv/fm, compared to controls. Treatment with SA + Cd increased pigment levels and fv/fm compared to Cd alone. Cd treatment led to a decrease in DW of total membrane lipids in leaves and depressed levels of monogalactosyldiacylglycerol and phosphatidic acid in leaves and roots of both cultivars. The effects of SA priming and SA + Cd treatment on lipid content and composition were cultivar-specific, suggesting that lipid metabolism may not be a primary target underlying SA remediation of the damaging effects of Cd on wheat growth and development.

Peanut (Arachis hypogaea L.) is the fourth most cultivated oilseed in the world, but its cultivation is subject to fluctuations in water demand. Current studies of tolerance between cultivars and physiological mechanisms involved in plant recovery after drought are insufficient for selection of tolerant cultivars. We evaluated tolerance of different peanut cultivars to water deficit and subsequent rehydration, based on physiological and biochemical status. Gas exchange, photosynthetic pigments, F/F, MDA, HO and antioxidant enzyme activity were analysed. Drought stress and rehydration triggered distinct changes in pigments, F/F, gas exchange, and HO across genotypes, with increased MDA in all cultivars under stress. Based on multivariate analysis, 'IAC Sempre Verde' was identified as most drought sensitive, while 'IAC OL3', 'IAC 503', and 'IAC OL6' exhibited variations in physiological responses and antioxidant activity correlated to their respective tolerance levels. Notably, 'IAC OL3' had higher WUE and enhanced enzymatic defence and was classified as the most drought tolerant in this context. The above findings suggest that antioxidant metabolism is a important factor for plant recovery post-rehydration. Our study provides insights into antioxidant and physiological responses of peanut cultivars, which can support breeding programs for selection of drought-tolerant genotypes. Future field studies should be conducted for a better understanding of tolerance of these cultivars, particularly through correlation of these data with crop yield impact.

Hybrid zones offer unique insight into reproductive barriers and plant speciation mechanisms. This study investigated postzygotic reproductive isolation in the natural hybrid Epidendrum × purpureum, which occurs in sympatry with its parent species, Epidendrum denticulatum and E. orchidiflorum. We examined the development of male and female gametophytes and the events leading to seed formation in this hybrid zone. Floral buds and flowers from E. × purpureum individuals were collected at various stages of development. Both self-pollination and backcrosses between hybrids and parental species were performed to follow ovule and seed development up to 60 days after pollination. The material was analysed using optical and confocal microscopy. In most hybrids, microsporogenesis and microgametogenesis occur regularly, forming viable male gametophytes. Non-viable male gametophytes were also observed and are the result of symmetrical mitotic division. The development of the female gametophyte occurs after self-pollination, and proceeds regularly, resulting in a reduced female gametophyte. Embryo development in the parental species occurs without abnormalities, while in backcrosses between hybrids and parental species, most embryos degenerate. Embryo degeneration in the crosses between hybrids can be explained by genetic incompatibilities. The co-occurrence of viable embryos and degenerating embryos in backcrosses between hybrids and parental species point to incomplete postzygotic reproductive barriers between the hybrid and the progenitors. Our findings suggest that E. × purpureum could facilitate gene flow between parental species, as much of its embryological development occurs without abnormalities.

Drought stress severely impedes plant growth, development, and yield. Therefore, it is critical to uncover the genetic mechanisms underlying drought resistance to ensure future food security. To identify the genetic controls of these responses in Sorghum, an agriculturally and economically important grain crop, an interspecific recombinant inbred line (RIL) population was established by crossing a domesticated inbred line of Sorghum bicolor (TX7000) with its wild relative, Sorghum propinquum. This RIL population was evaluated under drought conditions, allowing for the identification of quantitative trait loci (QTL) that contribute to drought resistance. We detected eight QTL in the drought population that explain a significant portion of the observed variation for four traits (height, aboveground biomass, relative water content, and leaf temperature/transpiration). The allelic effects of, and the candidate genes within, these QTL emphasize: (1) the influence of domestication on drought-responsive phenotypes, such as height and aboveground biomass, and (2) how control of water uptake and/or loss can be driven by species-specific plant architecture. Our findings shed light on the interconnected roles of shoot and root responses in drought resistance as it relates to regulation of water uptake and/or loss, while the detected allelic effects demonstrate how maintenance of grain production and yield under drought is a likely result of domestication-derived drought tolerance.

Plant-microbe interactions significantly influence plant growth dynamics and adaptability. This study explores the impact of metabolites on microbial biodiversity in shoot tips and wood of Populus nigra under greenhouse conditions, using high-throughput sequencing and metabolite profiling. Branches from P. nigra were harvested, rooted, and transplanted into pots for growth. After 3 months, tissue samples from shoot tips and wood were collected, and metabolites extracted and analysed using GC-MS and LC-MS. Genomic DNA was extracted and subjected to high-throughput sequencing for bacterial biodiversity profiling. Both datasets were analysed using bioinformatic and statistical pipelines. Metabolite profiling indicated that shoot tips had a higher relative abundance of primary and secondary metabolites, including sugars, fatty acids, organic acids, phenolic acid derivatives and salicinoids, while wood was enriched in flavonoids. Bacterial biodiversity also differed significantly between these tissues, with Clostridiales, Bacteroidales and Bacillales dominating in shoot tips, associated with rapid growth and anaerobic fermentation, while wood tissues were characterized by diazotrophs from Rhizobiales, Sphingomonadales and Frankiales. PCoA clustering confirmed tissue-specific microbial differences. Functional analysis revealed an enrichment of fundamental cellular processes in shoot tips, while wood exhibited pathways related to degradation and mortality. Metabolite profiling revealed significant variations in primary and secondary metabolites, highlighting their influence on microbial biodiversity across plant tissues. The dominance of specific bacterial orders and distinct functional pathways in each tissue suggests a tailored microbial response to the unique environments of shoot tips and wood.

Cold resistance in fruit trees has a direct impact on food production and scientific studies. 'Donghe No.1' is an excellent cold-tolerant peach variety. Metabolomic changes under freezing stress were examined to understand the mechanisms of cold adaptation. The UPLC-MS/MS system was used to identify differentially expressed metabolites (DEMs) in branches of 'Donghe No.1' under freezing stress for 12 h at -5°C, -20°C, -25°C, or -30°C. In total, 1096 metabolites and 196 DEMs were obtained at -5°C vs -20°C, -25°C, and - 30°C, while 179 DEMs and eight shared DEMs obtained at -5°C vs -20°C, -20°C vs -25°C, and -25°C vs -30°C. KEGG enrichment identified 196 DEMs associated with amino acid metabolism, linoleic acid metabolism, alpha-linolenic acid metabolism, phenylpropanoid biosynthesis, and flavonoid biosynthesis under freezing stress. A metabolic network in 1-year-old peach branches under freezing stress is proposed. Moreover, these results enhance understanding of metabolite responses and mechanisms to freezing stress in peach and will help in future breeding of freezing-tolerant varieties and investigating tolerance mechanisms.

Tropical rainforests are hot and may be particularly sensitive to ongoing anthropogenic global warming. This has led to increased interest in the thermotolerance of tropical trees. Thermotolerance of leaves of two tropical tree species, Terminalia catappa and Coccoloba uvifera, was determined by exposing leaf samples to 15-min heat treatments, followed by measurements of potential photosystem II quantum yield (dark-adapted value of variable/maximum chlorophyll a fluorescence, F/F) after 24 h and 14 days, and visible damage (necrosis) after 14 days. T (24 h), the temperature at which F/F declined by 50% 24 h after heat treatments, was associated with only ~10% leaf area damage in C. uvifera and no damage in T. catappa. In neither species was leaf necrosis observed at T (24 h), the temperature at which F/F declined by 5%. In both species, temperatures significantly higher than T (24 h) were required for 50% leaf area necrosis to occur. T (14 days) was a better proxy of visible leaf damage than T (24 h). The relationship between heat-induced F/F decline and tissue necrosis varies among species. In species surveys of leaf thermal tolerances, calibration of the F/F assay against the necrosis test is recommended for each species under investigation. F/F measurements soon after heat exposure do not reliably predict irreversible heat damage and may thus not be suitable to model and predict the thermostability of tropical forest trees.

Developing melon genotypes with resistance to Fusarium oxysporum f. sp. Melonis-(FOM) race1.2 is a major goal in any breeding program. In this study, we identified the role of 11 gene markers that contribute to polygenic resistance during the FOM1.2-melon interaction. qRT-PCR analysis elucidated upregulation of candidate marker genes AMT, DXPR, Fom-2, GLUC, GalS, GRF3, MLO, PRK, RuBlsCo, TLP and WRKY in resistant 'Shante-F1' and 'Khatouni', and susceptible 'Shante-T' and 'Shahabadi' at 7, 14 and 21 days post-inoculation (dpi). We also studied changes in defence-related enzyme activity: chitinase (CHI), β-1,3-glucanase (GLU) and peroxidase (POX) in melon roots. AMT, GLUC and DXPR transcripts were upregulatied in leaf and root tissues of the resistant 'Shante-F1' and 'Shahabadi'. Transcript levels for GalS and GRF3 increased 6.77- and 6.83-fold in roots of 'Shante-F1' at 7 dpi, whereas in PRK, TLP and WRKY theye increased by 7.84-, 5.15- and 12.26-fold at 14 dpi, respectively. However, transcript levels increased by 5.18-fold for Fom-2 and 8.46-fold for MLO at 21 dpi. Also, RBC transcript level peaked at 14 dpi with 4.9-fold increase in leaves of resistant genotypes, whereas AMT increased 2.94-fold at 21 dpi, and GLUC and DXPR increased 7.11- and 2.91-fold at 14 dpi in 'Shante-F', respectively. Defence-related-enzyme activity was also upregulated three-fold in resistant varieties. The dynamic shifts in the melon transcriptome induced by FOM1.2 emphasize that resistance mechanisms are predominantly regulated through signalling pathways involving CHI, GLU, and POX defence response. Surprisingly, the AMT gene, basically resistant to downy mildew, Pseudoperonospora cubensis; GLUC, MLO and PRK resistant to powdery mildew (Sphaerotheca fusca); TLP and WRKY resistant to Phytophthora blight (Phytophthora capsici); and GRF3 and RBC resistant to root knot nematodes (Meloidogyne spp.) were upregulated in resistant genotypes, indicating a dual role of these genes in resistance to more than one disease at a time.

Plants synthesize a broad array of specialized chemical compounds that mediate their interactions with the surrounding environment. Some of this chemical diversity is functional and subject to natural selection, but the factors underlying chemical evolution at the intraspecific level remain largely unknown. Here, we combined chemical, environmental and genetic data to investigate the effect of aridity on the expression of chemotypes in the invasive shrub Senecio pterophorus. We studied the variation in pyrrolizidine alkaloids (PAs), a group of specialized metabolites widespread across the families Boraginaceae, Asteraceae and Fabaceae, from native populations spanning a cline of aridity and from three cross-continental introductions, under natural and common garden conditions. We examined whether the relationship between chemistry and aridity was compatible with a process of adaptive differentiation using a method that partitions the variance and covariance by controlling for the population neutral genetic structure. We found a consistent shift from retrorsine-like to seneciphylline-like compounds under increasing aridity in both natural and controlled conditions in coherence with the biosynthetic pathways. This pattern was independent of the neutral genetic structure and occurred along the environmental gradient in the native range and in a convergent manner in all nonnative regions, which suggests adaptive differentiation in response to aridity. Our findings show that the diversity of PAs in S. pterophorus has been partially shaped by aridity. Investigating how abiotic factors influence chemical evolution is key to elucidating the plant responses in future climate scenarios and the cascading effects on other trophic levels.