PREMISE:In semiarid ecosystems such as the Brazilian Caatinga, physical seed dormancy (PY) is critical for plant persistence when water is unpredictable, but how soil moisture and temperature regulate PY release and seed longevity in species of native Fabaceae that have different growth forms is unknown. METHODS:Seeds of the herbaceous species Centrosema pascuorum and Crotalaria retusa and tree species Mimosa ophthalmocentra, M. tenuiflora, and Piptadenia retusa were collected in the Caatinga and tested in the field and laboratory to assess dormancy, viability, and germination. Seeds were either buried at the collection site and periodically exhumed over 15 months, or stored dry or with wet-dry cycles at constant or fluctuating temperatures. RESULTS:Seeds of herbaceous species had rapid PY release and seed depletion shortly after the onset of rainfall, leading to synchronized seedling emergence. Seeds of the trees M. ophthalmocentra and M. tenuiflora maintained high dormancy and viability, indicating strong potential for persistent soil seed banks, whereas seeds of Piptadenia retusa had low persistence due to rapid dormancy loss and high mortality. Across species, PY release was maximized under wet-dry cycles at high temperatures, revealing a synergistic effect of moisture pulses and heat. CONCLUSIONS:Temperature-moisture interactions characteristic of the Caatinga control PY release and seed persistence, with growth form shaping contrasting regeneration strategies. The delayed release of PY in trees spreads germination over time, enhancing persistence under unpredictable rainfall. Early PY release in herbs optimizes exploitation of short favorable windows to complete their rapid life cycle.
PREMISE:Medullary bundles, which are vascular bundles in the pith, have evolved multiple times. However, their functional significance remains poorly understood. Here, we investigated how medullary bundles are involved in the vascular architecture and hydraulic function in a tropical root climber, Adelobotrys scandens (Melastomataceae) to understand the functional significance of this vascular architecture in a wet-adapted root climber species as compared to what is known about medullary bundles in the lineages in hydraulically limited arid/saline environments. METHODS:We used light microscopy to examine the organization of the medullary bundles in the stem. We measured the hydraulic conductivity of intact stems and compared it with those of stems that were experimentally reduced to pith tissue. These analyses allowed estimation of hydraulic conductivity through the pith tissue system. RESULTS:Adelobotrys adscendens has a polycyclic eustele, with procambium-derived medullary bundles of two types: peripheric bundles forming leaf traces and cauline bundles forming sympodia at nodal regions of stems. Although the pith has low intrinsic hydraulic conductivity, pith tissues contributed up to 80% of total stem hydraulic conductivity near the apex, before secondary xylem becomes the dominant hydraulic pathway. CONCLUSIONS:Our experimental study enhances the understanding of atypical vasculature in woody plants. We demonstrated that medullary bundles function in plant water balance, particularly in water transport processes in leaf traces and young shoots, where the pith dominates stem cross-sectional investment. We discuss how this type of vasculature is involved in the evolution of life forms that develop aerial adventitious roots.
PREMISE:Restoring plant communities is increasingly challenging with climate change. While practitioners have traditionally used local seed sources, many are recommending assisted migration, possibly from more extreme environments such as inland rather than coastal environments, for restoration. METHODS:We compared the performance of four dominant Southern California shrub species, grown from seed from either coastal (mean 17.11°C) or inland (mean 19.28°C) populations, in a coastal common garden site under three levels of water availability. The goal was to test whether inland populations had higher survival, growth, and reproduction than coastal populations when experiencing the extreme highs and lows of water availability currently observed inland that mimic possible future climate conditions in coastal regions. RESULTS:Plants of most species generally grew less and had fewer flowers with water reduction, but neither flowering nor growth were strongly or consistently affected by seed source. Within our coastal common garden site, survivorship of coastal-sourced plants was higher than survivorship for inland-sourced plants. An interaction between seed source and water treatment influenced survivorship of all species, such that the negative effect of decreased water was more pronounced for inland-sourced plants. This effect might be explained by the physiological trait measurements which indicated stomatal conductance of Eriogonum and Salvia was higher for inland-sourced populations, suggesting increased water use. CONCLUSIONS:Collectively, these findings indicate that the dominant shrub species in this coastal Mediterranean ecosystem are sensitive to reduced water, and assisted migration from inland to coastal environments will not improve restoration outcomes.
PREMISE:The identity of sterile floral organs in second-whorl, alternisepalous positions within Caryophyllaceae remains contentious, having been described as staminodes, "petaloids," or petals homologous with those of other Pentapetalae. Limited ingroup and outgroup sampling and floral developmental data and inadequate phylogenetic comparative methods in previous studies have added to this uncertainty. Crucially, staminodes have not been analyzed as discrete characters, leaving their homology with other structures unresolved. METHODS:We reconstructed a chronogram of 775 species using five fossil calibrations for Caryophyllaceae and outgroups. Floral traits of 613 species, including number and position of petal-like structures, staminodes, and stamens, were quantified. Stochastic character mapping estimated ancestral character states and transition rates. Literature reviews provided developmental data to characterize common floral forms; transition models were used to assessed patterns of floral development and evolution. RESULTS:Staminodes evolved at the root of an apetalous Caryophyllaceae and were maintained throughout the backbone, being lost multiple times and becoming petal-like, especially in the Plurcaryophyllaceae in which a second whorl of stamens evolved in the alternisepalous position through the splitting of the alternisepalous primordia. The Caryophyllaceae crown ancestor likely had a single whorl of antesepalous stamens alternating with alternisepalous staminodes. CONCLUSIONS:Caryophyllaceae flowers are apetalous: All alternisepalous sterile structures are staminodes. Since their origin, staminodes have subsequently undergone multiple instances of loss, reduction, and elaboration. Their evolutionary history parallels patterns in early angiosperm lineages, making Caryophyllaceae a valuable system for investigating the role of staminodes in floral function and diversification.
PREMISE:Floral scent is central to host recognition in the fig-fig wasp mutualism, yet how scent divergence relates to pollinator sharing among closely related dioecious Ficus species remains unclear. METHODS:We analyzed volatile organic compounds (VOCs) from four pairs of closely related Ficus species that have different levels of pollinator sharing (complete, partial, or none). Floral scent profiles were compared using multivariate analyses, and their relationship with genetic distance was evaluated using a Mantel test. RESULTS:Floral scent profiles differed among species and were shaped by both genetic relatedness and pollinator sharing. Nonmetric multidimensional scaling (NMDS) ordination revealed clear clustering of species based on scent composition, and a PERMANOVA revealed significant interspecific differences, except between F. auriculata and F. oligodon, which share pollinators and have similar VOC profiles. In general, species pairs that share pollinators had greater similarity in scent composition than those that did not, although this pattern was not universal. Floral scent similarity declined with increasing genetic distance (Mantel test: r = -0.39, P = 0.041), indicating that closely related species tend to have more similar scent profiles. CONCLUSIONS:Floral scent similarity is partly associated with pollinator sharing in closely related Ficus species, but this relationship is not consistent and likely depends on additional factors, including genetic divergence and ecological context. Overall, floral scent variation reflects the combined influence of evolutionary history and ecological processes. Broader taxonomic sampling and functional analyses of pollinator responses are needed to further clarify these relationships.
Across the tree of life, and particularly within land plants, there is a wide diversity and disparity of genome structure. The most well-studied are angiosperms, comprising mostly small and dynamic genomes, with a history of ancient whole genome duplications. Genome structure and evolution have historically been less clear in ferns and lycophytes, and the origin of their large genomes and high chromosome numbers has been debated for decades, centering on differences in reproductive mode (heterospory and homospory). Klekowski (1973) hypothesized that homosporous ferns and lycophytes were mainly inbreeding and that polyploidy allowed for higher genetic diversity via homoeologous heterozygosity. In contrast, Haufler (1987) and others proposed that homosporous ferns and lycophytes had diploid inheritance and outcrossed frequently, a theory supported by genetic crossing, isozymes, and modern comparative genomic analyses. This article summarizes past and current theories on the mechanisms of genome evolution in homosporous plants, highlights the contributions of comparative genomics to this field in the past two decades, and discusses what we may be able to learn by considering the role of meiosis in heterosporous and homosporous fern and lycophyte genome structure.
PREMISE:Root hemiparasites form haustoria in belowground roots of hosts to extract nutrients and water from the surrounding hosts. Through parasitic symbiosis, these plants disproportionately affect plant communities relative to their abundance by reducing host size, altering nutrient flow, and eventually increasing local biodiversity. Their prevalence and potential as keystone species position hemiparasites as important drivers of community structure. METHODS:In a 2-year study at the Rocky Mountain Biological Laboratory, we selected paired presence and absence plots for three species of hemiparasitic Castilleja across seven study sites to explore the association of Castilleja with differences in the structure of montane plant communities. Our objectives were to (1) observe the relationship between three hemiparasitic Castilleja species and plant community diversity and composition and (2) assess the host range and preference for each species in situ using direct and indirect sampling. Percentage cover of all species was recorded to assess the effect of Castilleja presence on plant community diversity and composition. To assess host range and preference and to support nearest-neighbor and indicator-species analyses, we excavated Castilleja individuals to observe haustorial connections. RESULTS:Across sites, species, and years, the presence of Castilleja was consistently correlated with increased plant biodiversity and site-specific differences in community composition. Excavations suggested that Castilleja species are generalist hemiparasites with some preference for common, dominant hosts. CONCLUSIONS:Our results identify a positive relationship between Castilleja presence and local plant community diversity and support the interpretation that these species act as generalist hemiparasites.
PREMISE:Node-internode modular units characterize the construction of many herbaceous stems such as those of bamboo culms, providing hydraulic conductance and mechanical support such that internode biomass inequality observed within a culm significantly influences growth and structural stability. However, this inequality has not been studied. Traditional metrics, such as the coefficient of variation (CV), and the Gini coefficient (GC), can obscure sources of variation. METHODS:To address this analytical gap, we used the performance equation (PE) and its generalized version (GPE) to fit the rotated and right-shifted Lorenz curve (RRLC) of the internode mass distribution to quantify the inequality of each of 835 culms of 14 Phyllostachys species. The adjusted root mean square error and corrected Akaike information criterion were used to compare contending equations. Based on the better model fit, the Lorenz asymmetry coefficient (LAC) was calculated to determine whether many large (or a few large) internodes contribute to the within-culm inequality of the internode mass distribution. RESULTS:The GPE was significantly better than the PE in describing the RRLC. The mean LAC was 0.6436 (±0.0273 SD), which was significantly greater than 0.5, indicating that the inequality in internode mass is primarily driven by many rather than a few large internodes. CONCLUSIONS:These findings highlight a mechanical reinforcement strategy in bamboo whereby biomass is preferentially allocated to lower internodes to enhance flexural stiffness to deal with gravitational and wind-induced dynamic loads. The RRLC-LAC framework is shown to be effective in elucidating the biomass allocation strategies that balance growth with structural support.
PREMISE:Intraindividual variation in reiterated structures (e.g., leaves) represents an important dimension of phenotypic variation that contributes to functional diversity and the dynamics of ecological communities. It can be expressed differently across plant traits, but how environmental drivers affect intraindividual variation in different trait types remains unknown. METHODS:Here we subjected Galium odoratum to drought and shading treatments with a full-factorial experimental design to investigate environmental induction of intraindividual variation in vegetative, phenological, and floral traits and the dynamic relationships between trait mean responses and their variation. RESULTS:Intraindividual variation differed in magnitude between trait types, with vegetative traits having the highest variation and floral traits the lowest. Intraindividual variation differed among the environmental treatments with floral traits having the highest variation under control conditions, whereas vegetative traits had the highest amount of variation under the combined drought and early-shading treatment. Relationships between intraindividual variation and trait means varied across most traits and treatments, indicating environmentally induced dynamics in trait expressions. CONCLUSIONS:Intraindividual variation was environmentally inducible and dynamic depending on the treatment, suggesting that plastic responses in intraindividual variation may be an important component for mechanistic adjustments of plants to environmental stresses.
PREMISE:Tulips are one of the best-known geophytes, but their taxonomy remains convoluted and their evolutionary history poorly understood. Here, we used plastid genomes to identify some issues with current classification, understand the diversification history of the genus, and identify potential species linked to historical cultivation. METHODS:We gathered a large number of tulip specimens from living collections, herbaria, and online sources and through extensive fieldwork to infer maximum likelihood phylogenies of the plastid genomes of Tulipa (Liliaceae), representing ~86% of accepted species alongside a range of occasionally accepted synonyms. We used BEAST and secondary calibration points to date the tree, before assessing the biogeographical history of the genus using BioGeoBEARS. RESULTS:Based on our results, we described a fifth subgenus, Eduardoregelia, and identified a range of species where our results do not align with current taxonomy. Our data suggests the genus diverged from a clade containing Amana and Erythronium around 32.5 million years ago (Mya), with the most recent common ancestor existing around 22.8 Mya in the broader Central Asia region, a period that saw rapid uplift of mountain ranges and associated aridification in the region. The genus primarily diversified in Central Asia with rapid radiations within the last 10 My, possibly as a response to further orogenesis. Several migrations outside of the ancestral region have occurred, primarily via the steppes of Kazakhstan and Russia and along the Caucasus and Iranian and Anatolian Mountains to the eastern Mediterranean region. We also provide evidence that the maternal lineage of the garden tulip involved several species including T. scardica and T. suaveolens. CONCLUSIONS:Many tulip species present limited diagnostic characters, making their taxonomy difficult, compounded by their long use in horticulture and widespread hybridization, especially in gardens. We provide an up-to-date phylogenetic framework for this genus that may help resolve many taxonomic issues in the future, while highlighting further work to be done. We reinforce the importance of Central Asia in the evolutionary history of this genus and provide an important foundation for further study of Tulipa and more effective conservation of wild tulip species.
PREMISE:The fossil record of Lauraceae extends back to the Early Cretaceous and comprises numerous flowers. However, phylogenetic relationships of many of these fossil flowers remain unresolved. To better understand the early evolutionary history of Lauraceae, we conducted phylogenetic analyses of living and extinct members of the family and described a new fossil flower from the Coniacian of British Columbia, Canada. METHODS:Serial sections of the new fossil flower were prepared and used to create a three-dimensional reconstruction. We performed a series of phylogenetic analyses, including total-evidence analyses using a novel morphological matrix, to analyze the new fossil flower and 16 previously described fossil flowers. Phylogenetic uncertainty was explored for each taxon, and phylogenetic pseudofossilization analyses were conducted to test whether our floral data set can accurately recover systematic relationships within Lauraceae. RESULTS:The Eden Main fossil flowers are assignable to Lauraceae and represent a new genus and species: Extroparvum occidentale. Phylogenetic analyses recovered E. occidentale and 12 fossil flowers among Lauraceae. Phylogenetic uncertainty within Lauraceae was high for many of the fossils, but we identified two taxa as crown-group members that can be employed as new node calibrations for the family. Pseudofossilization analyses indicated that our floral data set can accurately recover taxa within crown-group Lauraceae with high support. CONCLUSIONS:Our work adds to the known Cretaceous diversity of Lauraceae and provides the first phylogenetic evidence of crown-group Lauraceae diversifying by the Late Cretaceous. Furthermore, our novel morphological data set lays an important foundation for directly integrating fossil flowers into macroevolutionary studies of the family.
PREMISE:This study describes three new records of Icacinaceae-Punctiuga bachue gen. et sp. nov., Palaeophytocrene paramoae sp. nov., and Goweria bacatana sp. nov. from the Paleocene (Selandian-Thanetian) Bogotá Formation in Colombia-improving understanding of the distribution and evolution of this family in the Neotropics. METHODS:We analyzed 47 fossil endocarps using microscopy and X-ray micro-computed tomography (μCT); we also studied the associated leaf assemblage in search of potential Icacinaceae foliage. We then compared the fossils to extant Icacinaceae specimens from herbaria and the existing literature. RESULTS:Punctiuga bachue features unique morphological traits that resemble and support a close affinity to Iodeae and Phytocreneae. The presence of Palaeophytocrene paramoae confirms Phytocreneae diversity in South America during the Paleocene, and the occurrence of leaves of Icacinaceae contribute to the history of Icacinaceae on the continent. CONCLUSIONS:Our results show a previously unacknowledged diversity of Icacinaceae in the Paleocene Neotropics, including two new species of endocarps with affinities to Phytocreneae and Iodeae, clades currently restricted to the Old World tropics. Our findings support an early Paleogene diversification of the family in the Neotropics and the extirpation of tropical lineages in the Neotropics during the later Cenozoic.
Premise Human activity has significantly altered the salt cycle, affecting an estimated 2.5 billion acres of soil worldwide. Elevated soil salinity is a well-known plant stressor, but it may also affect interactions between plants and insects, which are often sodium limited. Elevated sodium in nectar can increase pollinator visitation, but no previous study has examined the effects of elevated soil salinity on visitation by pollen-collecting bees.Methods Our study tested whether increased soil salinity impacts pollen sodium and Bombus spp. visitation to Solanum carolinense, a buzz-pollinated perennial wildflower that rewards pollinators only with pollen. Soil salinity around the root zone of Solanum carolinense growing wild in an early successional field was artificially increased with a salt solution to observe changes in pollen sodium and other cations, pollen viability, and pollinator visitation.Results Salt addition to the soil increased soil salinity by over five-fold, but there was no effect on the sodium levels of S. carolinense pollen. The salt treatment had no effect on pollinator visitation or pollen viability.Conclusions Although high soil salinity has been shown to increase nectar sodium levels and thus pollinator visitation, we infer from our results that S. carolinense is able to largely exclude sodium from its pollen, preventing high salinity soil from affecting pollinator attraction and pollen viability.
PREMISE:Temperature is a primary regulator of seed development. In seeds with morphological (MD) or morphophysiological (MPD) dormancy, embryo elongation represents a distinct postdispersal developmental phase that precedes germination. However, the thermal thresholds governing this embryo growth phase remain poorly quantified. We quantified species-specific embryo-growth thermal niches to provide a mechanistic framework for understanding regeneration timing and its evolutionary constraints. METHODS:We estimated cardinal temperatures-base (Tb), optimum (To), and maximum (Tm)-for embryo growth in 10 Apiaceae species, a family in which MD and MPD are very common due to the presence of underdeveloped embryos. Seeds were incubated at five temperatures (5-25°C) with and without gibberellic acid (GA3). Embryo growth rates were modeled using nonlinear thermal performance curves within a multimodel inference framework, followed by phylogenetic signal analyses. RESULTS:Substantial interspecific variation was found, with Tb ranging from 0 to 6.5°C, To from 5 to 25°C, and Tm from 21.5 to 31°C. GA3 generally increased growth rates and widened thermal ranges by reducing Tb and raising Tm, though responses were strongly species-specific. Phylogenetic analyses revealed significant signal for all thermal thresholds (Tb, To, Tm), indicating that evolutionary history constrains these thermal niches for postdispersal embryo growth. CONCLUSIONS:Postdispersal embryo growth constitutes a distinct, quantifiable thermal niche rather than a mere proxy for germination. By explicitly treating postdispersal embryo growth as a distinct thermal niche rather than a proxy for germination, this study extends thermal threshold theory to an overlooked developmental phase and provides a mechanistic framework for understanding dormancy release and regeneration timing under variable climatic conditions.
Premise : Bamboos have extremely long internodes, making it possible to measure tensile properties and anatomical features of discrete nodes and internodes and understand how the plants endure mechanical stress and how the tissues function in commercial products. We compared upper, middle, and lower parts of culms in black bamboo, Phyllostachys nigra, to determine whether the nodes comply with the Niklas spring-like joint model. Methods: We measured flexural stiffness, modulus of elasticity (E), load at failure (F-max), modulus of rupture (MOR), and density and fiber cap size of vascular bundles and assessed bundle orientations. Microcomputed tomography (microCT) during bending tests were used to determine sites of failure. Results: Regardless of shoot position, nodes were less stiff (lower E) and weaker (lower MOR) than adjacent internodes. However, F-max was similar or greater in the nodes, suggesting nodes absorb considerable strain energy. Vascular bundle density was highest in the top internodes and nodes. Apparently, in lower nodes, sustained primary growth thickened the ground tissue between bundles, while size of the fiber caps also increased. Whole-shoot bending experiments and microCT indicated that failure occurred first in hollow internodes parallel to the vertical vascular bundles, not at nodes. Conclusions : Vascular bundle positioning and composition allows nodes to bend and absorb considerable strain energy while resisting breakage, consistent with the spring-like joint model of the node. Sustained primary growth allows stems to thicken near the base to remain mechanically adequate. Bamboo nodes are thus areas of remarkable resilience; they will not break before internode tissue.
Premise Since its emergence in the Mesozoic, Sequoia (Cupressaceae) has been considered to possess conserved leaf morphology. However, recent studies have shown that the leaves of extant S. sempervirens become smaller, with a scale form, with increasing tree height. The fossil-genus Protosequoia has a similar scale leaf morphology, but its relationship to co-occurring Sequoia fossils, which bear linear leaves, remains unresolved.Methods To resolve this relationship, we re-examined specimens of two fossil species of Sequoia and Protosequoia from the Upper Miocene of Japan, focusing on leaf epidermal morphology and vascular bundle structure in the bract-scale complexes of seed cones.Results We identified fossil specimens with two types of shoots that were preserved in organic connection, but they had previously been classified as different genera. As the leaf shape changed from linear to scale, stomatal orientation shifted from parallel to the midrib to irregular, and epidermal cells gradually became shorter. Seed cones contained fewer than 30 bract-scale complexes with rhombic distal surfaces marked by horizontal grooves. In cross section, scales had rhombically arranged vascular bundles and several abaxial resin canals. Seeds had broad wings, and male strobili were mostly spherical.Conclusions The connected shoots, which shift in leaf stomatal features, and similarities in reproductive structure of the fossils suggest that the two genera represent the same species. Therefore, we propose a new Sequoia species characterized by densely branched twigs bearing smaller scale leaves, possibly reflecting an adaptation to different climatic conditions, compared to other species.
PREMISE:Resilience to the interaction of multiple stress factors of drought, wildfire, and canker disease has been little studied. During the 2012 to 2016 megadrought in California, black walnut trees were observed to resprout from the base due to water stress-induced dieback. After monitoring plants for a year, wildfire burned all the plants at two of our study sites, which was followed by vegetative resprouting. Plants also expressed symptoms of canker disease. We thus had an opportunity to assess the impacts of water stress, wildfire, growth form, and canker disease on plant performance. METHODS:Water potentials and photosynthetic rates of drought-induced resprouts were monitored and compared to nearby adults that had not experienced drought-induced dieback, both inland (San Dimas, California) and at coastal exposures (Malibu, CA). We monitored the recovery of adults and drought-induced resprouts from 2017 to 2019, including fire-induced resprouts at coastal exposures following a 2018 wildfire. In addition, stem canker number and canker length were compared among irrigated and non-irrigated growth forms, including drought-induced resprouts, coppice-induced resprouts, adults, and resprouting adults. RESULTS:Drought-induced resprouts displayed higher water potentials and photosynthetic rates than adults, especially during dry periods, but had lower (more negative) values than fire-induced resprouts. Non-irrigated walnut trees displayed greater canker initiation and canker elongation rates than irrigated trees, with irrigated coppice-induced resprouts showing the least canker development. CONCLUSIONS:Resprouting can temporarily relieve water stress, but xylem water stress and canker disease agents feed off one another. Repeat stresses of drought, fire and disease compound to reduce the resilience of individuals and populations of walnut.
PREMISE:Climate refugia endemics have persisted through past environmental shifts, but their responses to modern severe weather remain poorly understood. Torreya taxifolia (Taxaceae), a critically endangered conifer endemic to steephead ravines of Florida and Georgia, has declined for decades due to fungal canker diseases. Hurricane Michael, a Category 5 storm in 2018, caused extensive forest damage in its refugial habitat. We investigated how natural variation in disturbance was linked to tree health and microclimatic conditions relevant to disease. METHODS:We monitored the health and habitat of 40 wild T. taxifolia individuals for 4 years after the hurricane by measuring branch growth and mortality and temperature and light around each T. taxifolia. We assessed the abundance and area of fungal cankers. Hurricane disturbance was characterized using complementary metrics of forest structural change (basal area) and the size-weighted abundance of fallen and standing trees. RESULTS:Tree fall was associated with increased branch growth when quantified with summed diameter at breast height (DBH) metrics, but not with basal area metrics. Neither metric of tree fall was significantly associated with branch mortality. Local temperatures were positively associated with canker abundance, though not with total canker area, and were not directly linked to measures of forest change. CONCLUSIONS:Hurricane disturbance was associated with short-term after-storm growth responses among surviving T. taxifolia individuals, while warmer local conditions were linked to increased canker disease symptoms. Together, these results suggest that torreya growth was more closely associated with neighborhood-scale disturbance intensity than with broad reductions in stand-level biomass.
