American Journal of Botany

Species are the fundamental analytical units of evolutionary processes; thus evidence-based species delimitation is a crucial step for understanding species radiations. However, the task of delimiting species is particularly challenging in the context of a syngameon--a group of distinct, but closely related species that have incomplete reproductive isolation and frequently hybridize in nature. This problem is further exacerbated by the presence of cryptic species--species that are phenotypically distinct, though difficult to distinguish with gross morphology alone. Heuchera subsect. Heuchera comprises both clear and cryptic species within a syngameon that has seen study from morphological, experimental, and phylogenetic aspects. This group has long been recognized for its taxonomic complexity, namely two recognized hybrid zones with extreme morphological variation and persistent non-monophyly among parental populations. Here, we reassess species limits within Heuchera subsect. Heuchera, focusing on the hybrid complex between H. americana and H. richardsonii and adjacent H. americana populations. We use a multipronged approach with deep population-level sampling to 1) assess the genetic structure of 655 individuals across the geographic range of the H. americana group to identify genetic lineages and 2) assess the phenotypic diagnosability of these lineages. Despite extensive admixture and gene tree conflict, we find multiple cohesive lineages with diagnosable phenotypes. We recognize five species and three varieties within the H. americana group, one new and four resurrected. Our results demonstrate that even highly reticulate syngameons can be partitioned into meaningful taxonomic units with multiple lines of evidence.

Little is known about environmental drivers of opportunities for hybridization, but its phylogenetic distribution across species and areas is heterogeneous, suggesting that ecological traits may play an important role in concert with postzygotic isolation. Because plant-pollinator interactions are responsible for gene flow in most plant species, differences in the mosaic landscape of plant-pollinator interactions could explain why some plants are particularly prone to hybridization. Prezygotic isolation is mediated by sometimes complex pollen presentation; conversely, conserved pollination strategies would lead to evolutionary constraints on pollinator assemblage divergence in the speciation process and therefore predict higher opportunities for gene flow, although this hypothesis has yet to be tested. The plant taxonomic tribe Heuchereae (Saxifragaceae) is a well-characterized system for pollinator interactions and particularly for floral scent, the primary pollinator attractant in the group. Floral volatile organic compounds (VOCs) in this clade are hypervariable at the population level and are thought to be responsible for pollination selectivity, leading to divergent pollinator assemblages. Observing a contrast of hybridizing and non-hybridizing species, the levels of attractant divergence may therefore predict levels of hybridization. We investigated pollination biology in the plant genus Heuchera, notable for frequent interspecific gene flow compared to tribal relatives, asking whether high rates of hybridization may be associated with low interspecific divergence of VOCs and the pollinator assemblages they shape, using as our system the hybrid zone between H. americana var. americana and H. richardsonii in the midwestern USA. We optimized a closed-space collection and GC-MS (gas chromatography-mass spectrometry) protocol to characterize VOCs in Heuchera flowers. To identify floral visitation and effective pollinators we conducted pollination observations at 40 Heuchera populations over the span of two field seasons. GC-MS data from 89 Heuchera specimens representing 69 populations suggests that classes of VOCs, and to a large extent individual compounds, are shared within the hybrid complex while other Heuchera that are not thought to hybridize with these species have distinct species-specific compounds. Pollination observations and metabarcoding of pollinator pollen loads confirm shared effective pollinators in the hybrid zone and between adjacent parental populations. Attractant and visitation data considered together suggest that conservatism of pollinator interactions may be a typical feature associated with frequent hybridizers, perhaps arising from developmental or biochemical constraints on prezygotic isolation, and more broadly that the macroevolution of isolation mechanisms may be predictive of natural hybridization rate.

Abstract summaryThis report presents a preliminary bryoflora for Grand Staircase-Escalante National Monument (GSENM) in southern Utah. The inventory included over 1000 collections made across 40 localities (i.e. macrohabitat types) spanning two ecologically important gradients in bryophyte habitat: shade and moisture availability. At present, the growing checklist contains 117 taxa of liverworts and mosses including 27 families, 65 genera, 116 species, 9 varieties, and 1 subspecies. Noteworthy records include 49 putative taxa new for the state of Utah, and 2 undescribed species in the genera Grimmia and Schistidium. We propose 4 of these species be considered for addition to the recently revised bryoflora of North America. As expected for arid and semiarid environments, the bryophytes of GSENM are predominantly acrocarpous mosses (75%) followed by pleurocarpous mosses (16%), thalloid liverworts (7%), and leafy liverworts (2%). The most diverse families included xeric-soil acrocarpous mosses in the Pottiaceae (35%) and xeric-rock acrocarpous mosses in the Grimmiaceae (15%). Both xeric and mesic species were recovered in the Bryaceae (10% of species) while the pleurocarpous Amblystegiaceae included mesic and hydric species (7%). Most species in the bryoflora have broad global or disjunct distributions, but notably, the known distribution of 17 species appears limited in the United States, or globally, and warrant monitoring in GSENM. Using floristic habitat sampling across 19 macrohabitat types (combinations of 6 topography and 7 vegetation classes), mean site richness was 17.2 {+/-} 9 (SD) and ranged from 4 to 34 species. Six diversity hotspots supported [≥]30 species and were canyons with perennial or ephemeral streams dominated by mixed conifer, hardwood-riparian, riparian, or pinyon-juniper vegetation. High richness is likely supported by greater habitat diversity including xeric, mesic, and hydric conditions on variable substrates (e.g. rock, soil, biocrust, downed wood, seeps, and riparian aquatic/semi-aquatic habitat). Consequently, managing and monitoring diversity under future climate change and land-use alterations will necessitate a habitat-stratified approach that utilizes repeated floristic habitat sampling to document changes in site-level richness and to predict other candidate diversity hotspots on the basis of microhabitat-level diversity, which could be assessed by trained non-bryologists. Collection data are available to the public as georeferenced and photographed observations of half of the bryophyte collections on our iNaturalist.com project, Bryophytes of Grand Staircase Escalante, available for scientific, educational, or outreach activities. Observations are accessible to visitors (via the smartphone app) who wish to know what species have been found along popular trails in GSENM. Landscape-level richness may not reach that of the neighboring Grand Canyon National Park (>155 species), which supports a unique high-elevation bryophyte community sheltered in the mixed conifer and spruce-fir forests of the North Rims Kaibab Plateau. Future collecting by experts will inevitably uncover more species in this ecologically diverse monument important to conserving dryland bryophyte diversity and ecosystem function. This study will serve as a baseline for future research and long-term monitoring related to climate change impacts on dryland bryophytes including biocrust species. O_FIG O_LINKSMALLFIG WIDTH=158 HEIGHT=200 SRC="FIGDIR/small/708354v1_ufig1.gif" ALT="Figure 1"> View larger version (106K): org.highwire.dtl.DTLVardef@c50925org.highwire.dtl.DTLVardef@1db65c3org.highwire.dtl.DTLVardef@f60909org.highwire.dtl.DTLVardef@cb5244_HPS_FORMAT_FIGEXP M_FIG C_FIG Cover photos (by T. A. Clark): View of sandstone canyon wall along the Escalante River Trail taken during a July collection trip in 2015 (top) during which riparian bryophytes were collected by authro, T. A. Clark, (shown in photo) at a sandstone seep (bottom). Bureau of Land Managements National Landscape Conservation System Grant Cooperative Agreement #L14AC00275 issued to P.I. Lloyd R. Stark, UNLV O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=151 SRC="FIGDIR/small/708354v1_ufig2.gif" ALT="Figure 2"> View larger version (88K): org.highwire.dtl.DTLVardef@86109eorg.highwire.dtl.DTLVardef@1ad0efborg.highwire.dtl.DTLVardef@b2c239org.highwire.dtl.DTLVardef@1ed4a4a_HPS_FORMAT_FIGEXP M_FIG C_FIG Copyright 2020 by the authorsAll content contained herein is the property of the authors and all images the property of Theresa A. Clark and should not be used without permission except for education, in which case inclusion of the author/photographers name in citation or superimposed over any image(s) is requested.

AO_SCPLOWBSTRACTC_SCPLOWMulti-species communities of epiphytic bromeliads are a defining component of Neotropical canopies, yet we have little knowledge of how closely related species differ in the balance struck among vegetative growth, clonal propagation, and sexual reproduction. We compared reproductive output, clonality, and sexual systems in sympatric populations of Catopsis nutans (Sw.) Griseb. and Catopsis sessiliflora (Ruiz & Pav.) Mez occupying citrus groves in central Belize, sampling 235 reproductively mature individuals across 138 host trees in nine groves. Reproductive output, measured as the count of reproductive structures per individual, was modeled with negative binomial generalized linear mixed models that accounted for vegetative size and host tree identity. All sampled C. nutans were hermaphroditic, whereas all C. sessiliflora were unisexual, representing a dioecious population. Reproductive output increased with vegetative size in both species, and the scaling relationship did not differ between them despite their differing sexual systems. After accounting for size, C. sessiliflora produced more reproductive structures and more connected pups than C. nutans, and we found no evidence of a trade-off between clonal and sexual output in both species. Within C. sessiliflora, staminate individuals produced more flowers than pistillate individuals across comparable sizes. Co-occurring Catopsis can differ markedly in baseline reproductive and clonal output while sharing a conserved scaling of output on vegetative size, offering a foundation for further comparisons of sex-specific reproductive allometry in bromeliads.

Premise of the ResearchThe prevalence of sexual dimorphisms, which evolve due to contrasting strategies to maximize reproductive success in males and females, is variable among dioecious plant species. In the Salicaceae, many traits have been assessed across many studies, but direct or indirect associations between these traits and reproductive allocation are often neglected. Given the dynamic evolution of sex determination systems and the strong interest in wood production in the family, we wondered whether sexual dimorphisms related to reproduction may have gone unreported. Here, we assess sexual dimorphism in reproductive traits in two species of Salix. Recognition of reproductive sexually dimorphic traits will contribute to understanding the evolution of sex determination systems in the Salicaceae. MethodologyWe conducted observational studies in natural populations to assess the presence of sexual dimorphisms in early spring bud density, catkin number, and flower number per catkin across four sampling periods in Salix exigua. We also analyzed flower number and catkin number per flower in Salix nigra. Pivotal ResultsWe observed no sexual dimorphism in pre-season buds per branch in S. exigua but did find that males produced more flowers per catkin and more catkins per branch than females in both S. exigua and S. nigra. ConclusionsHigher flower numbers in males compared to females is consistent with expectations from intra-sexual selection among males. The presence of reproductive sexual dimorphisms in Salix suggests that sexual selection may affect the evolution of mating strategies in Salix species, and the evolution of the sex determination system within this genus.

The genus Solidago represents a taxonomically challenging group due to its sheer number of species, putative hybridization, polyploidy, and shallow genetic divergence among species. Here we use a dataset obtained exclusively from herbarium specimens to evaluate the status of Solidago ulmifolia var. palmeri, a morphologically subtle taxon potentially confined to Alabama, Arkansas, Mississippi, and Missouri. A multivariate analysis of both discrete and continuous morphological data revealed no clear distinction between S. ulmifolia var. palmeri and Solidago ulmifolia var. ulmifolia. Solidago ulmifolia var. palmeris status was also assessed with a phylogenomic and SNP clustering analysis of data generated with the "Angiosperms353" probe kit. Neither analysis supported Solidago ulmifolia var. palmeri as a distinct taxon, and we suggest that this name should be discarded. The status of Solidago delicatula (formerly known as Solidago ulmifolia var. microphylla) was also assessed. Both morphological and phylogenic analyses supported the species status of S. delicatula and we suggest maintaining this species at its current rank. These results highlight the utility of the Angiosperms353 probe kit, both with herbarium tissue and at lower taxonomic levels. Indeed, this is the first study to utilize this kit to identify genetic groups within a species.

Recent reviews of isolating barriers in plants conclude that prezygotic barriers play an outsized role in plant speciation; yet these conclusions derive overwhelmingly from studies of sympatric, perennial herbs in temperate zones, and at later stages of speciation. Trees possess several traits that are expected to influence barrier evolution, including prolonged generation times and reproduction, predominant outcrossing, and long-distance gene flow. We examined early-evolving post-pollination barriers between ecologically diverged, vegetatively distinct varieties of the tree species, Metrosideros polymorpha, that have a common floral morphology and highly overlapping flowering times. We performed controlled crosses between each of Hawaii Islands four varieties and maternal trees of the high-elevation variety and examined pollen-tube growth, fruit set, seed germination, and seedling phenotype. We then monitored survivorship, maturation rate, and fertility of F1 hybrids over [≥]8 years alongside parental controls and a fourth F1 genotype derived from companion studies. The four F1 crosses showed four contrasting patterns and strengths of predominantly postzygotic isolation, including high F1 mortality that manifested over several years. Results from this and other tree studies suggest that ecological speciation in trees follows the classical speciation model of early postzygotic barrier formation followed by reinforcement, whenever stable environments promote recurring hybridization.

PREMISE OF THE STUDYThe size and shape (physiognomy) of woody, dicotyledonous angiosperm leaves are correlated with climate and these relationships have been used to develop. proxies. These proxies assume that leaf morphology plastically responds to meteorological conditions and that leaf traits change isometrically through development.\n\nMETHODSWe used Digital Leaf Physiognomy (DiLP) to measure leaf characters of multiple Vitis species from the USDA Germplasm Repository in Geneva, NY from the 2012-2013 and 2014-2015 growing seasons. These growing seasons had different temperature and precipitation.\n\nKEY RESULTSWe found three primary results: (1) there were predictable significant differences in leaf characters in leaves of different developmental stages along the vine, (2) there were significant differences in leaf characters in leaves of the same developmental stage between the growing seasons, and (3) there were significant differences in leaf characters between growing seasons.\n\nCONCLUSIONSWe found that Vitis leaf shape had the strongest relationship with growing season meteorological conditions in taxa growing in their native range. In addition, leaves have variable phenotypic plasticity along the vine. We interpret that the meteorological signal was strongest in those leaves that have completed allometric expansion. This is significant for leaf physiognomic-paleoclimate proxies because these leaves are most likely to be preserved in leaf litter and reflect the type of leaves included in paleoclimate reconstructions. We found that leaf development does have the potential to be a confounding factor, but it is unlikely to exert a significant influence on analysis due to differential preservation potential.

SO_SCPLOWUMMARYC_SCPLOWO_LIThe tree of life is riddled with reticulate evolutionary histories, and some clades, such as the eastern standing Phlox, appear to be hotspots of hybridization. In this group there are two cases of reinforcement and nine hypothesized hybrid species. Given the historical importance of this group for our understanding of plant speciation, the relationships of these taxa and the role of hybridization and gene flow in their diversification require genomic validation. C_LIO_LIUsing phylogenomic analyses, we resolve the evolutionary relationships of the eastern standing Phlox and test hypotheses about if and how hybridization and gene flow were creative forces in their diversification. C_LIO_LIOur results provide novel resolution of the phylogenetic relationships in this group, including well-supported paraphyly across some species. We identify gene flow during one of two cases of reinforcement and find support for one of the five hypothesized homoploid hybrid speciation events. Additionally, we infer the ancestries of four allotetraploid hybrid species. C_LIO_LIHybridization has contributed to diverse evolutionary outcomes within this Phlox group; although, not as extensively as previously hypothesized. This study demonstrates the importance of phylogenomics in confirming hypothesized histories of non-model systems and adds to the growing evidence of interspecific genetic exchange in the generation of biodiversity. C_LI

PREMISE OF THE STUDYLife history is an important predictor of population genetic variation, although this link remains unexplored in numerous important plant lineages. One such lineage is the legume genus Strophostyles, which contains both annual and herbaceous perennial vines native to eastern North America. Specifically, it remains to be determined whether Strophostyles species with different life histories show different patterns of genetic differentiation and diversity, as well as if these species hybridize across their range. METHODSHere we sampled the perennial Strophostyles helvola and annual S. leiosperma in five sites across a latitudinal transect in the central United States, including three sites where the species occur in sympatry. Using genotyping-by-sequencing, we identified 5556 polymorphic SNPs across 166 individuals. KEY RESULTSThere is no evidence that Strophostyles helvola and S. leiosperma hybridize in the populations examined. Within species, Strophostyles helvola (perennial) displays admixture among populations, while S. leiosperma (annual) does not, although both species show more genetic diversity among rather than within populations. Patterns of genetic diversity are varied across populations of both species, with both heterozygote excess and deficiency. CONCLUSIONSThe complex patterns of genetic differentiation and diversity warrant further investigation of life history and population dynamics in Strophostyles, particularly mating system and modes of gene flow. This study exemplifies the diversity of population genetic patterns even within a small genus, and it reinforces the need to characterize such diversity in non-model systems to gain a more complete understanding of how life history contributes to population genetics.

Sexual dimorphism in plant growth and/or reproductive responses to the surrounding environment has been documented in some plant species. In gynodioecious plants, it is especially important to understand whether females and hermaphrodites differ in their response to environmental stressors, as the fitness of females relative to hermaphrodites determines the extent to which these separate sexes are maintained in natural populations. Soil nutrient availability is of particular importance given the different nutrient requirements of male and female sexual functions in plants. Here, we evaluated and compared the growth of females and hermaphrodites of Geranium maculatum in response to varying levels of nutrients. Using a greenhouse experiment, we manipulated the overall nutrient, nitrogen, and phosphorus levels in the soil and measured growth, allocation, and leaf quality responses in both females and hermaphrodites. We found that sexes responded similarly in their growth and allocation responses to nutrient availability, albeit evidence that female leaf chlorophyll content may have increased more than that of hermaphrodites across soil nitrogen levels. Our findings demonstrate that hermaphrodites differ from females in terms of their physiological response to varying nutrient levels, however these physiological differences did not translate into meaningful growth or reproduction differences.

PremiseIn plants, meristic traits, such as petal and sepal numbers, are usually considered invariant within taxa, yet certain species consistently exhibit great variability in these traits. The factors contributing to "atypical" counts are not well-known, published hypotheses include relaxation of pollinator selection, inbreeding, and hybridization, among others. The sand verbenas, Abronia (Nyctaginaceae), usually have five perianth lobes ( petals), yet certain taxa exhibit marked departures from this norm. MethodsHere we integrate an analysis of images from community science data (iNaturalist) and common garden experiments to evaluate a comprehensive set of adaptive and nonadaptive explanations for the production of these atypical flowers across an evolutionary transition from xenogamy (outcrossing) to autogamy (selfing) in the coastal sand verbena Abronia umbellata. Key resultsThe shift to autogamy in this lineage correlated with a higher frequency of atypical flowers from ~7% to ~20% and a significant reduction in mean petal number per inflorescence. Autogamous success did not change with petal number, and neither hybridization or up to three generations of inbreeding consistently increased production of atypical flowers or decreased mean petal number, all in contrast to previously-published hypotheses. In contrast, intra-inflorescence, inter-plant (intra-population), inter-population, and inter-variety comparisons demonstrated a correlation of reduced floral size with reduced petal number, suggesting correlated evolution due to a well-established relation between organ number and meristem size. ConclusionsThe reduction in petal number was probably a consequence of selection for smaller flowers associated with increased selfing. While we could not completely eliminate several alternative hypotheses, including a long-term history of inbreeding or relaxed selection on petal number constancy, those are less likely to explain the observed changes, though they may have contributed to the trend. In general, we develop a framework of hypotheses for evolutionary investigations of meristic variation in floral organs.

The frequency of hybridization differs strongly across different taxa and areas of Earth, yet the environmental drivers of this variation remain poorly understood. Areas strongly influenced by Pleistocene glaciation have long been hypothesized to be rich in hybrid taxa through forcing previously allopatric species into contact and interrupting ecological barriers. Here, we revisit naturally occurring Heuchera americana x H. richardsonii in North America using deep population level sampling of nuclear and plastid genomes to re-evaluate the long-standing hypothesis that Pleistocene climate dynamics promoted hybridization in this system. An extensive population-level sampling scheme involving nuclear and plastid genetic data (729 individuals across 455 populations) reveals a more complex hybridization history than implied by previous representative phylogenetic sampling. Our analyses identify multiple independent chloroplast capture events since diversification within this complex, rather than a previously hypothesized single ancestral event. Strong geographic structure at higher-level plastid clades but little structure within subclades, together with the rarity of ancestral plastid genomes, suggests a unidirectional inheritance of the introgressed plastid genome rather than a simple geographic distribution of plastid haplotypes. Ancestral niche projections indicate that Pleistocene glacial maxima created a shared narrow eastern refugium east of the Mississippi River, enabling localized hybridization, while western refugia were larger and taxa probably allopatric. This contrast led to an east-west gradient in cytonuclear discord. Our results corroborate and refine a 90-year-old hypothesis of climate-mediated hybridization by demonstrating that historical gene flow was spatially restricted but hybrid genotypes now command a larger geographic area. Our study highlights the importance of deep population-level sampling for accurately reconstructing hybridization histories and underscores the catalytic role of climatic instability in general as a driver of hybridization in Heuchera, and likely many other taxa across the tree of life.

The genus Rumex is a unique member of the Polygonaceae (Buckwheat) family of plants. A source of intrigue for Rumex lies in the diversity of the reproductive systems associated with the subgenera, species, and subspecies within this genus. Four previously circumscribed subgenera, some 200 species, and a number of subspecies comprise the collective Rumex genus. These species exhibit monoecious, dioecious, synoecious (hermaphroditic), and polygamous reproductive systems. Moreover, some of the dioecious species contain sex chromosomes, a phenomenon that is very rare in angiosperms. Apart from the confirmed morphological and phytogeographical distinctions, two of the four described subgenera, Acetosa and Acetosella, are distinctive in their exhibited sex chromosome systems. For this study, we used three chloroplast markers, rbcL, trnH-psbA, trnL-F, and dense taxon sampling, to reconstruct a molecular phylogeny for Rumex.The reconstructed phylogeny for this work resolves six major clades and one large grade in Rumex. In addition, the species with known dioecious reproductive systems derived from unique sex chromosome systems are resolved in two different clades nested within "the dioecious clade". These results suggest that the species with divergent sexual systems are more closely related to each other than to other species comprising the rest of the Rumex genus. Furthermore, some species with known synoecious reproductive systems are resolved in a single clade which is also nested within "the dioecious clade". These results imply a possible reversal occurring over time which suggests the highly plastic nature of reproductive systems among Rumex species.

PremiseUnderstanding how arid-adapted plants have diversified in harsh environments is a central question in evolutionary biology. Linanthus (Polemoniaceae) occurs in biodiverse dry areas of Western North America and exhibits extensive floral trait variation, multiple color polymorphisms, differences in blooming time, and variation in life history strategies. Here, we reconstruct the evolutionary history of this group. MethodsWe generated restriction-site associated (ddRAD) sequences for 180 individuals and target capture (TC) sequences for 63 individuals, with complete species sampling. Using maximum likelihood and pseudo-coalescent approaches, we inferred phylogenies of Linanthus and used these phylogenies to model the evolution of phenotypic traits and investigate the geographic speciation history of this genus. Key resultsShallow relationships are consistent and well supported with both ddRAD and TC data. Most species are monophyletic despite rampant local sympatry and range overlap, suggesting strong isolating barriers. The non-monophyly of some species is possibly due to rapid speciation or issues with current species delimitation. Perenniality likely evolved from annuality, a rare shift in angiosperms. Night blooming evolved three times independently. Flower color polymorphism is an evolutionarily labile trait and is likely ancestral. No single geographic mode of speciation characterizes the radiation but most species overlap in range, suggesting they evolved in parapatry. ConclusionsOur results illustrate the complexity of phylogenetic inference for recent radiations, even with multiple sources of genomic data and extensive sampling. This analysis provides a foundation to understand aridity adaptations, such as evolution of flower color polymorphisms, night blooming, and perenniality, as well as speciation mechanisms.

Solanaceae are a globally distributed family of considerable economic importance. Recent phylogenetic work on various clades in the family has resulted in a plethora of names at various taxonomic levels. This results in a confusing set of names applied to clades at different ranks, and to the use of informal names that are often not accepted in online resources. To solve this problem, we present here a phylogenetic classification following the PhyloCode for the Solanaceae. Traditional taxon names previously recognized at the ranks of tribe, genus, and section were maintained when associated with clades. We base our clade definitions on a newly constructed phylogeny of the family using 10 plastid and nuclear markers with a broad sampling of 1,474 species, roughly half of the diversity of the family. We complement this marker-based analysis with a phylogenomic analysis of 110 taxa (including 97 of the 102 genera in the family) using the Angiosperms353 probe set. This pair of analyses produced highly concordant phylogenies and provides strong support for the clades included in the classification. In total, we propose and define rank-free names for 38 major clades, including 16 infrageneric taxa within the mega-diverse Solanum. This rank-free system intends to promote name stability as new data become available, avoiding name changes to well-known groups.

Premise of researchWhat maintains mixed selfing and outcrossing is an enduring mystery in evolutionary biology. Cleistogamy, where individuals produce both potentially outcrossing chasmogamous and obligately selfing cleistogamous flowers, provides an ideal framework in which to study the evolutionary forces maintaining mixed-mating. Despite their promise for providing insight into mating system evolution, few studies of cleistogamous species have comprehensively investigated the relative costs and benefits of cleistogamous selfing. MethodologyWe quantified the necessary components to calculate the relative energetic cost of reproduction of the different flower types in three natural populations of the perennial Ruellia humilis Nutt (Acanthaceae). These components include flower dry mass, fertility (fruit set), and seed mass and number per fruit. We also measured pollen-ovule ratios for both flower types as another measure of relative energetic investment. We additionally tracked phenology of the two flower types and used the proportion of chasmogamous flowers to estimate maximum potential outcrossing rates. Pivotal ResultsWe found that the energetic cost of reproduction via cleistogamous flowers was about 4-10 times less than that of reproduction via chasmogamous flowers, and this energetic economy was from both reduced mass and increased fertility of cleistogamous flowers. Pollen ovule ratios in cleistogamous flowers were one third to one half those of chasmogamous flowers, providing additional support for their energetic economy. Maximum potential outcrossing rates in these populations based on chasmogamous flower production were between 43-61%, but chasmogamous flowers can autogamously self at rates of 33-75%. ConclusionsThe relative energetic economy of cleistogamous flowers suggest that progeny from chasmogamous flowers would have to have 4-10 times greater relative fitness to explain their evolutionary maintenance. These values are likely even greater considering the reduced investment in pollen production in cleistogamous flowers. Ongoing work will quantify potential advantages of chasmogamous flowers due to inbreeding depression and heterosis.

O_LIFloral nectar is a crucial energy source for many insects, yet its availability is rarely quantified at broad taxonomic and geographic scales. Mosquitoes are opportunistic nectar feeders whose survival and vectorial capacity depend on access to sugar resources, but the extent to which nectar sugar availability can be predicted from floral morphology across floras remains poorly understood. C_LIO_LIWe analysed relationships between corolla morphology and nectar traits in 156 flowering plant species from the UK and Zambia. Corolla length, base width and floral shape were measured alongside nectar volume and sugar concentration. Linear and linear mixed-effects models were used to assess predictive relationships in tubular and non-tubular flowers, and phylogenetic statistics (Blombergs K and Pagels {lambda}) were applied to test for evolutionary signal. C_LIO_LINectar volume and sugar content increased with tube length and width in tubular flowers, while corolla width and shape were strong predictors in non-tubular flowers. Phylogenetic analyses across 154 species (42 families) indicated weak phylogenetic signal in nectar volume. C_LIO_LISimple floral traits provide proxies for nectar sugar availability across lineages. Shape-specific scaling relationships suggest convergent responses to ecological and morphological constraints, offering a practical framework for predicting nectar resources and linking floral diversity to mosquito and pollinator ecology. C_LI

Using conventional statistical approaches there exist powerful methods to classify shapes. Embedded in morphospaces is information that allows us to visualize theoretical leaves. These unmeasured leaves are never considered nor how the negative morphospace can inform us about the forces responsible for shaping leaf morphology. Here, we model leaf shape using an allometric indicator of leaf size, the ratio of vein to blade areas. The borders of the observable morphospace are restricted by constraints and define an orthogonal grid of developmental and evolutionary effects which can predict the shapes of possible grapevine leaves. Leaves in the genus Vitis are found to fully occupy morphospace available to them. From this morphospace we predict the developmental and evolutionary shapes of grapevine leaves that are not only possible, but exist, and argue that rather than explaining leaf shape in terms of discrete nodes or species, that a continuous model is more appropriate.

Anthropogenic climate change and land-use changes threaten the health and survival of plants, particularly by altering the microclimatic conditions of habitats. Plant productivity is highly sensitive to these abiotic conditions that influence their morphological and physiological traits. I studied this relationship in plants of the Arctostaphylos genus, commonly known as manzanita, shrubs in chaparral ecosystems across California. I assessed microclimate and examined its effects on leaf morphological traits and plant productivity of A. crustacea ssp. crustacea across two sites in Alameda County, California. At the site of higher sunlight and less soil moisture (VWC), leaves had a greater mass per area (LMA) and were more steeply angled, and photosynthesis was significantly higher (11.14 {micro}molCO2/m2s) than leaves at the site of less sunlight and more VWC (7.94 {micro}molCO2/m2s). Results from linear mixed models showed that light level was the overall strongest predictor variable for plant traits, with vapor pressure deficit and VWC also contributing to LMA, and leaf temperature and leaf angle distribution also influencing photosynthesis. Overall, no individual microclimatic variable was the sole contributing predictor of a leaf morphological trait or photosynthesis. Rather a combination and interaction of microclimatic conditions influenced plant functional traits, though some conditions had greater influence than others. The functional traits of A. crustacea ssp. crustacea adjusted in response to microclimatic factors, showing intraspecific trait variation (ITV) of this species. ITV is an essential defense for plant resilience that allows for adaptations in the face of rapidly changing climatic conditions.