Annals of Botany

Background and AimsDistylous polymorphisms (distyly) are adaptations for plants to improve efficiency of cross-pollination and reduce pollen wastage. Theoretical models suggest that distyly evolves from stylar monomorphism via an intermediate stage of stigma-height dimorphism (SHD), however, this evolutionary scenario is only observed in few distylous lineages. The genus Jasminum have many species exhibit either distyly or SHD, providing an ideal opportunity to test models of the evolution of distyly. Focusing on the evolution of distyly, we investigated floral morphs and evaluated the occurrence of distyly and SHD in Jasminum using phylogenetic reconstruction and morphological analysis. MethodsWe investigated floral morphs and evaluated the occurrence of distyly and stigma-height dimorphism through morphology observation. To perform phylogenetic analysis, we sequenced plastomes of forty species from Jasminum and Chrysojasminum using Illumina next generation sequencing, and then constructed phylogenetic tree using maximum likelihood method and Bayesian inference. Based on the phylogenetic tree, we inferred the ancestral floral type through ancestral reconstruction. Key ResultsOur results suggest that the distyly originated in the common ancestor of Jasminum and Chrysojasminum. SHD occurs in several Jasminum species scattered in different clades of the phylogenetic tree, suggesting multiple independent reversions from distyly back to SHD. However, this transition is not associated with the loss of ancillary polymorphisms, as all the species examined in this study well retain dimorphic traits for other floral organs such as pollens and stigmas. Moreover, most species maintain strict heteromorphic self-incompatibility, while J. officinale has lost or at least partially lost self-incompatibility, suggesting that distyly is not always linked to self-incompatibility. ConclusionsIn Jasminum, breakdown of distyly resulted in evolutionary transitions to stigma-height dimorphism for multiple times, suggesting that distyly is not a stable floral polymorphism under certain selective forces. These findings advance our understanding on the evolution of distyly and plant reproductive systems.

Telomeres have the crucial role of protecting chromosome ends and its length varies significantly between organisms. What evolutionary factor shapes this natural variation has been a long standing question, with answers providing insights into chromosome function and evolution. In animals life-history variation relating to senescence or tumorigenesis explains telomere length variation. For plants, however, we lack knowledge of what factor is driving their length variation in nature. Is life-history differences also driving telomere length variation among plant species? We answer this question by analyzing the telomeres of 257 plant species spanning the major orders of the green plant kingdom. Telomere lengths were estimated for species that vary significantly in their life-history, geographical distribution, and trait characters. Results showed telomere length increased with the evolution of terrestrialization, where Chlorophytes had the shortest telomeres and Spermatophytes had the longest telomeres. Surprisingly, plants with different life-histories had minimal telomere length differences, but biogeographic clines had significant effect on telomere length variation. Plant telomere length increases closer to the equator, while telomere length decreases at higher altitude. Domestication was previously proposed to lengthen telomeres, but we found no consistent domestication effect on telomere lengths comparing crops and their wild progenitors. From our results we conclude plant telomere length contrasts with animal telomeres, in that life-history has minimal effect on length variation. Instead we propose the ecological adaptation hypothesis, where telomere length in plants is determined by selection from abiotic conditions, and suggest temperature is a major factor shaping telomere length in plants.

Background and Aims Epiphytes comprise approximately 10% of global vascular plant diversity and play key roles in many tropical ecosystems. They possess traits allowing survival under limited water availability (i.e. the epiphytic trait syndrome), but knowledge of these trait combinations is taxonomically biased and their generality remains unclear. The megadiverse genus Anthurium (Araceae), with ~600 epiphytic species, offers an opportunity to address this gap by examining patterns of leaf trait covariation, their phylogenetic context, and differences among life forms. Methods A common garden experiment was conducted using 40 species from 13 sections spanning a gradient of epiphytic incidence. Twenty-one anatomical, morphological, and physiological leaf traits were quantified. Patterns of trait variation were assessed, and associations between leaf traits and epiphytism were evaluated both with and without accounting for phylogenetic relationships. Key Results Leaf trait variation was captured by two principal components. The first axis was negatively associated with stomatal density and size, leaf thickness, and leaf water content, while the second axis described a trade-off between leaf mass per area (LMA) and water loss rate. Epiphytic species generally exhibited smaller, more numerous stomata and higher LMA, consistent with adaptations for water retention. Epiphytism showed a phylogenetic signal; however, trait covariation patterns were not influenced by phylogenetic relatedness. Conclusions We found consistent associations between epiphytism and several water-related leaf traits in Anthurium, but some of these associations departed from general expectations of an epiphytic trait syndrome. Water-related traits showed variable phylogenetic signal and reflected multiple functional strategies for coping with intermittent water supply. These findings highlight the diversity of functional strategies underlying epiphytism and expand current understanding beyond well-studied taxa.

1. Most plant species are genetically differentiated among populations, often reflected by phenotypic trait variation that corresponds to local adaptation. Yet the strength of local adaptation and heritable contribution to phenotypic traits vary across traits, species, and environments. Additionally, climate change is rapidly altering environmental conditions, and the climate may shift faster than populations can adapt or track the change via dispersal, resulting in adaptive lags. However, it remains unclear how widespread such adaptive lags are across plant species. 2. We focused on Hordeum murinum, an annual ruderal grass widespread in Europe. We combined continental-scale in situ measurements of 2070 plants across 207 populations with common garden experiments across two contrasting climates and two soil types to disentangle heritable variation from phenotypic plasticity and assess potential adaptive lags under climate change. 3. We found that heritable variation was pronounced in developmental traits, particularly flowering time and plant height, while seed weight, reproductive investment and SLA showed intermediate heritable contribution, and flag leaf area and total biomass were primarily plastic. Heritable trait variation was strongly associated with temperature at the populations origin, and trait clines were consistent with in situ patterns, suggesting that temperature is the main driver of genetic differentiation in H. murinum. However, we detected that fitness peaked in populations originating from warmer climates, indicating that evolutionary responses may not keep pace with rapid environmental shifts. 4. Synthesis: Our results highlight that H. murinum harbors substantial heritable variation, shaped primarily by temperature. However, the pace of evolutionary change may be insufficient to track ongoing climate change, leaving populations potentially vulnerable to future environmental conditions.

In plants, ecological interactions such as pollination depend on whole-plant phenotypes, where coordinated variation among vegetative, floral, and reproductive traits can shape reproductive success. However, empirical studies linking integrated phenotypes that include non-floral traits to reproductive outcomes within populations remain limited. While prior work has shown that crimson monkeyflowers exhibit heritable variation in foliar anthocyanin striping, the functional significance of the trait has been thus far unknown. Using plants derived from natural populations, we conducted field and greenhouse experiments to assess whether foliar striping is genetically correlated with traits related to pollinator attraction. We found that foliar striped plants consistently exhibit larger flowers, greater nectar rewards, and decreased proportions of viable pollen relative to non-striped plants. When we manipulated flowers within plants with and without foliar striping to allow only outcrossing or only self-fertilization in a field environment, we found that outcrossed flowers had higher reproductive success than did self-fertilized, with outcrossed flowers from plants with foliar striping producing the highest overall seed numbers and seed mass. Our results reveal patterns of coordinated foliar and floral trait variation and associated reproductive output that are consistent with a pollination syndrome framework. The link between foliar pigmentation and increased per-calyx reproductive output represents a novel association between foliar pigmentation and a broader evolutionary and ecological function.

The Himalayan-Tibetan-Hengduan (HTH) region is the richest biodiversity hotspot for high-elevation plants. However, owing to its remote and physically challenging topography as well as the trans-national nature of the region, many taxonomic problems in the area remain unresolved, particularly in the Himalaya. This, in turn, has impeded our understanding of the assembly of its extraordinary high-elevation flora. Here, we resolve phylogenetic relationships and delimit species in a distinctive clade of honeysuckles that is endemic to the HTH, the Isoxylosteum clade of Lonicera, using restriction-site associated DNA sequencing (RADseq) and morphological data. Five species complexes of Isoxylosteum have standardly been recognized. Three of these complexes are highly variable and have been divided into several varieties or species each. Phylogenetic, population structure, and morphological analyses of leaf and floral traits from samples collected across the range of the clade support the recognition of five species, including a species that has most often been recognized as a variety of L. rupicola (L. rupicola var. minuta). Instead, we find that it is sister to L. spinosa. This is surprising because the geographic range of L. minuta is contiguous with the other varieties of L. rupicola in the northern Hengduan region but widely separated from L. spinosa whose range lies mainly to the west of the Tibetan plateau. On close examination we find that several morphological and ecological traits also support a closer relation of L. minuta to L. spinosa. None of the other eight previously recognized varieties and species were supported. Floral traits showed high discriminatory power, correctly classifying 89% of samples to species. By comparison, leaf dimensions classified species with 59% accuracy. Our results identify diagnostic morphological apomorphies for each recognized species and major clade and provide a revised taxonomic framework for Isoxylosteum.

Asian Passifloraceae occupy a distinctive evolutionary and ecological position within the family despite their relatively low species diversity compared with the Neotropics. Many Asian representatives are highly localized, small and often ephemeral climbers that persist seasonally through rhizomes, tuberous stems or dormant seeds, while considerable morphological plasticity may obscure species limits and evolutionary relationships. Xishuangbanna, southwestern China, lies at the convergence of Southeast Asian, Indian-Himalayan and southern Chinese floristic elements and represents an important regional centre of Passifloraceae diversity, with two species of Adenia and five species of Passiflora, including the recently described P. xishuangbannaensis and P. menghaiensis. We investigate the evolutionary relationships, plastome evolution and population genomics of these taxa using complete plastome assemblies, a concatenated dataset of 68 selected plastid protein-coding genes, 356 reconstructed nuclear Coding Sequences (CDS), and Genotyping-By-Sequencing (GBS) across the known wild distribution of P. xishuangbannaensis. Plastid, concatenated nuclear and nuclear coalescent phylogenies were strongly incongruent and differed from published classifications based on morphology and earlier phylogenies (ITS, ncpGS, ctyGS, ndhF and trnL-F). Gene-tree discordance and phylogenetic-network inference indicated widespread incomplete lineage sorting together with introgression. The two statistically best-supported network models placed P. menghaiensis, which showed high genetic similarity to the Indian P. napalensis, as a sister lineage involved in independent reticulation events associated with P. altebilobata, P. xishuangbannaensis and P. sumatrana. A pronounced biogeographic pattern was evident within Passiflora supersection Disemma, particularly in the P. siamica-P. cochinchinensis lineage across the Hua Line, whereas relationships among other Asian Passiflora blurred this boundary. This pattern suggests that diversification and reticulation within the Asian lineage may have overlapped temporally with the development of the biogeographic divide represented by the Hua Line. The concentration of early-diverging lineages around Xishuangbanna and the eastern Himalayan-Indian region further points to this area as an important centre in the early diversification of Asian Passiflora. Within this context, the highly localized P. xishuangbannaensis may represent either a relictual of an early Asian lineage or the surviving product of an ancient reticulate complex, contrasting with lineages such as P. siamica that subsequently expanded farther across Southeast Asia. Comparative plastome analyses revealed extensive structural and gene-content evolution within subgenus Decaloba, including pseudogenization, gene and intron losses, and repeated Inverted-Repeat (IR) expansions and contractions; substantial plastome modification also characterized supersection Disemma. Passiflora sumatrana exhibited a particularly distinctive IR expansion extending into the accD-pafII region, potentially characterizing this lineage. Adenia plastomes were generally more structurally conservative, although A. penangiana displayed an IR-boundary contraction involving the rps19-rpl2 region. Mitochondrial CDS and non-coding regions provided the best-resolved phylogenetic signal and revealed strong discordance with the chloroplast phylogeny, consistent with maternal mitochondrial inheritance and variable plastid transmission, potentially involving paternal or biparental inheritance and heteroplasmy. GBS analyses of P. xishuangbannaensis using complementary distant-reference, de novo and closely related-reference approaches showed that mapping to P. organensis provided the clearest SNP distribution and population resolution. ADMIXTURE, PCA and FST analyses revealed two strongly geographically structured populations with additional substructure and substantial differentiation (FST = 0.112). Linkage disequilibrium based demographic reconstruction using GONE2 indicated declining effective population size (Ne) toward the present in both populations, with a particularly abrupt recent decline in Pop1 and a more gradual decline in Pop2. Few candidate Self-Incompatibility (SI) genes could be confidently reconstructed, including limited recovery of highly variable docking regions. However, the intracellular region of an S-locus Receptor Kinases (SRK) contained a distinctive non-synonymous substitution predicted to alter protein configuration without major disruption of overall folding, potentially contributing to compatibility differences between populations. Together, these results reveal a complex evolutionary history combining historical dispersal, incomplete lineage sorting, reticulation, morphological plasticity, plastome structural evolution and strong population differentiation. The narrow distributions and recent demographic decline of these newly recognized Xishuangbanna taxa emphasize their conservation importance, while broader Asian taxon sampling and deeper genomic sequencing will be essential to resolve the evolutionary history of this discreet and poorly known Passifloraceae radiation.

Extrafloral nectaries (EFNs) are a widespread plant defense mutualism trait and are highly convergent, appearing in hundreds of plant lineages worldwide. Here we investigate a report of possible EFNs in Erythranthe angulosa, a recently-described California wildflower. We integrate field observations, insect bioassays, an induction experiment, and microscopy to test for signatures of EFN function, finding no evidence that the distinctive axillary swellings produced by E. angulosa function as EFNs. We also uncovered two distinct morphs at the type locality of E. angulosa that diverge in the number of axillary swellings produced, as well as other shoot architecture traits such as stem thickness, leaf size, and branch number. Although the axillary swellings appear to not function as EFNs, they remain a compelling morphological variant within the yellow monkeyflowers that may perform storage or another unknown function.

Reports that the South American climbing vine Boquila trifoliolata modifies its leaf shape to mimic leaves of its host plant have raised considerable attention. Boquila leaf development was proposed to reflect visual inputs perceived in an unknown manner. However, the very existence of Boquila leaf shape mimicry remains inconclusive, since the reported observations are open to alternative explanations. We performed an initial quantitative characterization of leaf shape variability in glasshouse-cultured clonal Boquila plants grown without close host contact, and attempted to reproduce the leaf shape mimicry phenomenon under controlled culture conditions using live olive (Olea europaea) plants, artificial (decoy) olive or artificial ivy plants as supports. While we found leaves of variable shape (including those resembling ivy leaves) both in plants grown without host contact and in those climbing on live or decoy hosts, we did not observe any link between leaf shape and host presence or character. Instead, the leaf shape appears to be affected by environmental conditions including the season. Although our study was limited to a single Boquila genotype and an ecologically unrealistic host selection, our observations suggest that the alleged mimicry might originate from unintentional misinterpretation of intrinsic discontinuous leaf shape plasticity in field observations.

Balancing sexual reproduction with vegetative growth poses challenges for many plants. Additionally, reproductive effort, such as production of pollen or flowers, is not always correlated with numbers of viable and germinable seeds. Energetic tradeoffs like these can be particularly fraught for imperiled species and might be especially complicated in landscapes with a possibility of interspecific hybridization. In this multi-year study, we track the reproductive effort, flowering phenology, and reproductive output of two interfertile Sarracenia (pitcher plants). We show that reproductive effort varies among years and sites, and that production of pollen and flowers does not always result in higher seed output. We demonstrate that phenological overlap in the timing of flower production and pollen viability could enable hybridization, and that the more imperiled taxon produces fewer seeds per flower. Results have implications for conservation of these pitcher plants, management of hybridization in these and other systems, and general principles of reproductive allocation.

Polyploidization can profoundly affect plant metabolite biosynthesis, yet its influence on chemodiversity remains poorly understood, despite the central role of chemodiversity in mediating plant interactions with the environment. The coexistence of facultative apomictic and sexual reproductive systems across ploidy levels in Hypericum provides an excellent model for investigating the evolution of chemodiversity following polyploidization. We analyzed ploidy levels and leaf metabolic fingerprints across selected populations of three Hypericum taxa, H. maculatum, H. perforatum subsp. perforatum and H. perforatum subsp. veronense. Polyploidization was common across all three taxa. Leaf metabolic fingerprints were more pronouncedly differentiated by the ploidy level of the mother plant (F0) than that of the offspring (F1). Although unique metabolic features emerged in plants of most ploidy levels, diploid plants exhibited fewer metabolic features than polyploid plants. Higher Shannon diversity, functional Hill diversity, and intensities of features belonging to specific chemical families were associated with higher F0 ploidy levels in H. perforatum subsp. perforatum, but not in H. maculatum and H. perforatum subsp. veronense. Our findings demonstrate that polyploidization can lead to rapid shifts in chemodiversity across generations in Hypericum. The fast divergence in chemodiversity associated with polyploidization in H. perforatum may contribute to its remarkable invasive potential.

Myricaria Desv. (Tamaricaceae) is a genus of shrubs that play a keystone role in montane riparian ecosystems across Eurasia, shaping riverine habitats and supporting ecological function. The genus has a centre of origin in the Qinghai-Tibetan Plateau and exhibits a broad distribution, but many species boundaries are unresolved. Here, we present the first phylogenomic analysis of Myricaria using the Angiosperms353 target enrichment bait set, with sampling across its full geographic range. Off-target plastid loci were extracted from next-generation sequencing data using the CAPTUS bioinformatics pipeline. We infer species relationships using ASTRAL-IV and network analysis with SplitsTree, in conjunction with morphology. We also provide a taxonomic treatment of the genus, integrating our morphological observations and phylogenomic analyses for species delimitations. Based on our analyses, recognise two infrageneric sections: sect. Parallelantherae (containing only M. elegans) and sect. Myricaria (the remainder of the genus, with type species M. germanica). We also propose synonymising M. davurica, M. bracteata and M. squamosa with M. germanica. Although species boundaries in the Asian highlands remain unresolved, we conclude that the species M. elegans, M. germanica, M. laxiflora, M. longifolia, M. platyphylla, and M. pulcherrima are well-supported both phylogenomically and morphologically.

Sinia rhodoleuca, the sole species of the monotypic genus Sinia (Ochnaceae), was previously transferred to Sauvagesia based mainly on morphological similarities. However, its phylogenetic position has remained unresolved because molecular data for the species were unavailable. Here, we generated genomic data for Sinia rhodoleuca and reconstructed its phylogenetic position within Sauvagesieae. Our phylogenomic analyses consistently recovered Sinia rhodoleuca as sister to Indosinia, whereas the Neotropical Sauvagesia formed a distantly related lineage, rendering Sauvagesia broadly circumscribed non-monophyletic. Comparative morphological evidence further supports the close relationship between Sinia and Indosinia, particularly in their closely parallel secondary veins, lacerate stipules, and prominent petaloid staminodes, while differences in floral characters support their recognition as distinct genera. We therefore reinstate Sinia as a distinct genus and provide a revised taxonomic treatment of Sinia rhodoleuca. Our study demonstrates how phylogenomic evidence can resolve long-standing taxonomic uncertainties and reveal evolutionary relationships obscured by morphological similarity.

Hybridization is a powerful process in plant evolution generating reticulate patterns of speciation, introgression, and chloroplast capture. In the Petota clade of Solanum, which spans cultivated and wild potatoes, these processes cause much of the taxonomic complexity of the group. We examined the evolutionary history of the Commersoniana group (Solanum commersonii and S. malmeanum) relative to S. chacoense (Tuberosa Group) using an integrative framework of phylogenomics and morphology. With target-capture sequencing (Angiosperms353) of nuclear and plastid loci recovered from herbarium specimens, together with data mining we built nuclear and plastome phylogenies and ran symmetry tests, gene concordance analyses, and coalescent simulations to weigh incomplete lineage sorting against chloroplast capture. The data reveal cytonuclear discordance and events consistent with chloroplast capture from S. chacoense into Commersoniana lineages supported by both empirical and simulated results. Phylogenetic networks confirm repeated historical and recent reticulation, especially involving S. malmeanum. Non-metric Multidimensional Scaling (NMDS) of morphological traits did not recover clear species boundaries but was consistent with a hybrid origin for the group. These results indicate that recurrent hybridization and event consistent with chloroplast capture are strongly influencing evolution in the examined wild potatoes, complicating classical taxonomy and informing conservation and breeding. They also underscore the value of combining genomic and phenotypic data to resolve species boundaries in plant groups with tangled hybrid histories.

Seed ecophysiology is essential for understanding plant regeneration and developing effective conservation and ecological restoration strategies, yet knowledge remains scarce for most threatened Cerrado species. We characterised the germination niche, desiccation tolerance and storage behaviour of Xyris paradisiaca (Xyridaceae), an Endangered species endemic to Central Brazil, to assess whether its restricted distribution is associated with narrow germination requirements and to inform seed-based conservation. Germination was tested across light regimes, constant temperatures, decreasing water potentials and short-duration heat shocks, while thermal- and hydro-time models were used to quantify thermal and hydric thresholds. Seeds exhibited an absolute light requirement but broad abiotic tolerances. Germination remained >87% between 15 and 40 {degrees}C, with estimated cardinal temperatures of Tb = 8.94 {degrees}C, To = 33.13 {degrees}C and Tc = 45.53 {degrees}C. Germination remained similar to the control down to -0.6 MPa and exceeded 40% at -1.0 MPa, with a median base water potential of {Psi}b = -1.03 MPa. Germination also remained high after 1-min heat shocks up to 200 {degrees}C. Seeds were desiccation tolerant, with 100% germination after drying and a viability loss index of -0.04, and germination remained >90% after 24 months of ambient storage. Thus, the highly restricted distribution of X. paradisiaca is not driven by a narrow physiological germination niche. Its broad environmental tolerances, desiccation tolerance and favourable storage behaviour also highlight its unexplored potential for seed-based restoration, propagation and ex situ conservation.

Hybridization and introgression are thought to play key roles in the formation of biodiversity. However, detecting gene flow between species and understanding reticulation patterns remain challenging, especially in species-rich lineages with complex evolutionary histories. Adiantum is a large fern genus, and ecological studies in Amazonia have found that species identification is often difficult due to morphological similarity and overlapping characteristics among species. Although several hybrids have been described in tropical America, comprehensive studies investigating genetic exchanges in this genus are still lacking. We used chloroplast and nuclear phylogenomic data to examine evolutionary relationships among tropical American Adiantum species. By combining traditional phylogenetic analyses with advanced bioinformatic methods such as HybSeq-based target capture, reference-guided phasing (HybPhaser), and network-based analyses, we found widespread reticulate evolution involving both recent and ancient hybridization events. These were especially common among those species that have been difficult to delineate morphologically. Our findings indicate that reticulate evolution has played an important role in shaping the diversity of neotropical Adiantum, especially within the tetraphyllum lineage. Such widespread hybridization has no doubt contributed to morphological ambiguity and taxonomic challenges. Our integrated analytical approach provides a first attempt at untangling the reticulate evolutionary history in this group, and future studies with additional sampling can be expected to clarify the evolutionary processes further.

Premise Rising temperatures can reduce plant reproductive success by disrupting pollen development, yet little is known about how reproductive heat sensitivity varies among natural populations. We evaluated pollen viability responses to elevated temperature in two closely related taxa of yellow monkeyflowers across multiple geographic scales to determine whether heat sensitivity varies among species, between populations and across elevations. Methods We conducted three common garden growth chamber experiments. First, we compared pollen viability responses to heat stress between Mimulus guttatus and members of the M. tilingii species complex. Second, we tested whether broad elevational categories explained variation in heat responses. Third, we evaluated heat sensitivity among nine eastern Sierra Nevada populations of M. guttatus spanning an elevational gradient. Pollen viability was assessed following exposure to control and heat treatments. Key results Heat exposure reduced pollen viability in all experiments. In the species comparison experiment, pollen viability decreased more strongly in the high-elevation restricted M. tilingii species complex than the widespread M. guttatus. We found substantial population-level variation in pollen viability within M. guttatus but not members of the M. tilingii complex. Broad elevational categories did not explain this variation in pollen viability responses. However, within eastern Sierra Nevada populations, reductions in pollen viability became stronger with increasing source elevation. Several populations deviated from this trend, indicating reproductive responses to heat cannot be explained by elevation alone. Conclusions Pollen heat sensitivity varies substantially among species and populations of yellow monkeyflowers. Elevation alone is insufficient to predict pollen viability responses to elevated temperatures, suggesting that local adaptation or genetic variation may contribute to reproductive heat tolerance. Some populations of M. guttatus may contain greater capacity to maintain reproductive function under future warming, highlighting the importance of considering intraspecific variation when predicting plant responses to climate change.

Climate change is exposing trees to rising atmospheric water demand. Because stomata regulate plant water loss, understanding stomatal behaviour is critical. However, few comparative studies examine species-specific stomatal responses to atmospheric demand. Here, we quantify stomatal behaviour in 38 temperate tree species (27 broadleaved, 11 conifers) in a German research arboretum during a warm summer without soil drought. We measured the diurnal stomatal conductance (gs) of 787 leaves and modelled gs species-specific responses to leaf-to-air vapour pressure deficit (VPDL). Four descriptors of the gs-VPDL relationship were derived: maximum stomatal conductance (gmax), the VPDL that maximises gs, the VPDL associated with a 50% reduction in gs, and the stomatal closure rate. We relate these metrics to drought-induced shifts of carbon isotope ratios and to leaf functional traits. Large variation in stomatal behaviour exists, ranging from early-closure to VPDL-tolerant strategies. Species maintaining gs at higher VPDL also show weaker physiological responses to past drought. gmax is partly explained by leaf economic traits; other gs-VPDL descriptors are not related to stomatal anatomy and leaf economy. Our interspecific comparison reveals substantial variation in stomatal responses to atmospheric demand that is relevant to drought responses, but cannot be readily inferred from commonly measured leaf traits.

The Asparagaceae is an economically and ecologically important angiosperm (monocot) clade, containing iconic garden plants such as asparagus, hyacinth and agave, and arid-adapted keystone species like Joshua tree and dragon blood tree. The approximately 2,500 species in the family are spread across seven subfamilies: Agavoideae, Aphyllanthoideae, Asparagoideae, Brodiaeoideae, Lomandroideae, Nolinoideae and Scilloideae. Relationships among the seven subfamilies are generally unresolved and the sources of gene tree-species tree discordance are largely unknown. Investigating the biology underlying such discordance requires a robust sampling of both taxa and molecular markers, due to the extremely short branches that form the backbone of the Asparagaceae phylogeny. Using targeted sequencing of 1,726 low-copy nuclear genes, and a nearly complete sampling of genera, we interrogate relationships among all seven Asparagaceae subfamilies and investigate the underlying sources of discordance across the phylogeny. Analyses using different phylogenomic approaches (multispecies coalescence vs. nuclear gene supermatrix vs. chloroplast gene supermatrix) each revealed extensive discordance across the Asparagaceae backbone, which may be associated with rapid lineage diversifications that occurred in Africa shortly following the origin of the family ~49 Ma. Specifically, we found that two branches, representing ancestors of Aphyllanthoideae and Nolinoideae, may be responsible for much of the backbone discordance. The placement of Aphyllanthoideae, represented by one extant taxon (Aphyllanthes monspeliensis), is controversial with discordant topologies across many studies. However, multispecies coalescence-based analyses from this study strongly support a sister relationship between Aphyllanthoideae and a larger Agavoideae + Scilloideae + Brodiaeoideae clade. According to gene tree quartet frequencies and ABBA-BABA tests, we cannot reject incomplete lineage sorting (ILS) as the main source of discordance for the placement of Aphyllanthoideae; our results leave open the possibility of an ancient reticulation involving an ancestor of Aphyllanthoideae and an extinct basal Asparagaceae lineage. Regarding Nolinoideae, we found that conflicting support for two possible bifurcating clades (Asparagoideae + Nolinoideae vs. Asparagoideae + Lomandroideae) was associated with skewed support for alternative gene tree topologies, suggesting that phenomena other than ILS may explain the observed discordance. A quartet-based ABBA-BABA analysis, used to test for signatures of introgression, revealed a putative ancient hybridization event between two divergent, ancestral lineages which may have contributed to the origin of the Nolinoideae clade in Africa ~45 Ma. In sum, this study elucidates the long-troublesome backbone of the Asparagaceae phylogeny and advances our understanding of the evolutionary and biogeographical origins of all extant subfamilies. More broadly, this study expands our understanding of the various sources of gene tree discordance that may arise from natural processes associated with rapid lineage radiations across the tree of life.

Flower color has primarily been studied in the context of pollinator attraction, although effects on thermal energy balance are also important, especially in the context of global climate change. We used infrared imaging to compare petal temperatures of white versus pigmented cultivars of ten angiosperm taxa under controlled environmental conditions. Excised sets of flowers (n= 6 sets per species) exhibiting white, light, and/or dark anthocyanin (red to purple) coloration were mounted perpendicularly to the sun at mid-day, under clear sky, low wind (<1 m s-1) conditions. Sunlight was filtered through either UV-transparent or UV-opaque film, and petal temperatures were measured using an infrared camera after one minute equilibration. In all species, pigmented flowers were significantly warmer than lighter-colored conspecifics. Mean differences averaged +5.3{degrees}C for darker-colored versus white morphs, +2.9{degrees}C for lighter-colored versus white. Most warming was associated with visible wavelengths, but additional warming under UV-inclusion was also observed in some species. In situ observations of intact landscape plants under low-wind, high-light conditions corroborated experimental results, with differences exceeding 10{degrees}C observed in some taxa. Temperature differences >7{degrees}C were also recorded for purple versus white sections of the same flower in multicolored Viola and Petunia cultivars. Follow-up experiments using dark-pink and white varieties of Impatiens x hybrida corroborated well-known effects of sunlight intensity and wind speed on floral temperatures, helping to explain inconsistent reports in the literature. Our results clearly demonstrate that anthocyanin pigments can have significant and dramatic impacts on floral temperatures, which could be an important factor driving evolution of flower color. In the context of climate change, floral pigments could amplify the effects of rising global temperatures, negatively impacting plant reproduction and crop yields, especially on the warmer end of species ranges. Changes in flower color could also potentially induce shifts in pollinator communities, which could have community-scale effects.