Premise of research. Parasitic plants often experience reductions of the plastid genome (plastome), presumably as a result of relaxed selective pressure on genes relating to photosynthesis, eventually leading to pseudogenization and deletion. As such, parasitic plants are powerful case studies in evolutionary biology. One example is the orchid tribe Neottieae, which exhibits a range of trophic strategies including predominant autotrophy, partial mycoheterotrophy, and full mycoheterotrophy. Full mycoheterotrophy and the associated loss of photosynthesis are hypothesized to have evolved repeatedly in this clade, but the frequency and timing of these trophic shifts are not clear. While current models of plastome evolution in nonphotosynthetic plants focus primarily on the pattern of functional gene loss, few focus on the spatiotemporal and biogeographic aspects of this phenomenon. Methodology. Using long-read sequencing, we present the first complete plastome of the fully mycoheterotrophic North American Cephalanthera austiniae, also known as the phantom orchid, along with phylogenenomic and biogeographic analyses of Neottieae. Pivotal results. We present strong support for the placement of C. austiniae in a clade of leafy eastern Asian relatives, representing an independent transition to heterotrophy within the genus. Genomic analyses revealed that C. austiniae has lost a large portion of genes related to photosynthetic function. However, it notably retains putatively functional copies of members of the ATP synthase complex and the RuBisCO Large Subunit gene, known as rbcL. Biogeographic analyses provided evidence for relatively recent divergence of C. austiniae (ca. 2-7 Ma), likely descending from a leafy ancestor in eastern Asia or Beringia, and a subsequent loss of photosynthetic function following a disjunction caused by the closing of the Bering Land Bridge in the late Pliocene. Conclusions. We discuss the evolution of mycoheterotrophy in Neottieae, focused on C. austiniae, to demonstrate the utility of this clade for informing knowledge on the genomic consequences of mycoheterotrophy and to pose potential alternatives to models based purely on relaxed negative selection in heterotrophic plants. This work illustrates how integrating phylogenomics with biogeography can reveal the evolutionary mechanisms that shape and constrain the genomic trajectories of heterotrophic plants.
Premise of research. Two new taxa of gymnosperm fossil seeds and new specimens of Problematospermum ovale have been recovered from the Early Cretaceous of Mongolia and Inner Mongolia, China. All were recovered as lignite mesofossils from Mongolia, and one, Bugdaevaea lignitica gen. et. sp. nov., was also recovered in permineralized chert from Inner Mongolia, China. Methodology. Fossils were studied using light microscopy, semidestructive traditional sectioning, cellulose acetate peels, and X-ray microtomography. Pivotal results. Bugdaevaea lignitica is 4-6 mm long, slightly four angled in cross section, and obovate to fusiform in longitudinal section, with a collar that supports a long micropyle. Bugdaevaea lignitica has a two-layered seed envelope, in which a smooth outer layer covers a rugulate sclerenchymatic inner envelope. Nosovaea striata gen. et sp. nov. is 4-6.5 mm long and ovoid to spherical and tapers at the apex into an extended micropyle. The seed envelope has a thick cuticle covering a smooth sclerenchymatic seed envelope. Newly discovered specimens of P. ovale are 3-4.5 mm long and narrowly elliptical, with short, blunt ridges and a long micropyle. Conclusions. All three seed taxa are chlamydospermous in organization, with a seed envelope completely covering the integument except for the elongated micropylar projection. Specimens of P. ovale demonstrate that the seed envelope has longitudinal sutures and splits apically into five to seven valves. They also clarify the orientation of these seeds on the parent plant. The three seed species are structurally similar to the diverse chlamydospermous seeds previously treated as the Bennettitales-Erdtmanithecales-Gnetales group. The discoveries from Mongolia and China show that seeds of this kind were present in Early Cretaceous floras from central and eastern Asia and contribute further information on the diversity of a key group of extinct seed plants at a critical time in plant evolution.
In 1937, E. W. Berry described and identified a collection of fossil plants from Miocene-aged sediments in the Cumarebo oil field of northwestern Venezuela. Recent reviews of Berry's extensive publications on paleobotany, however, have revealed numerous incorrect identifications, which have complicated efforts to understand Neotropical paleofloras. Of particular interest is the fossil Gyrocarpus miocenica, for which many of its traits were incorrectly described, prompting a complete reexamination. We redescribed the fossil and compared its morphological features with modern and extinct members of Hernandiaceae, Dipterocarpaceae, Juglandaceae, Anacardiaceae, Malpighiaceae, and Betulaceae. Our investigation revealed strong similarities between Gyrocarpus miocenica and Tetrapterys (Malpighiaceae) based on distinct characters, including pericarpic wings and schizocarpic condition. Our combined morphological and molecular phylogenetic analysis showed strong support for its placement within the genus Tetrapterys, a member of the tribe Hiptageae. This leads us to reject it from Gyrocarpus and the Hernandeaceae and transfer it to the Malpighiaceae as Tetrapterys miocenica (E.W. Berry) Crook et al., comb. nov.
Premise of research. Compressions of unornamented, ribbed, and branched axes with regions of preserved anatomy were obtained from the Emsian of New Brunswick, Canada, and provided one of the first examples of secondary growth in Early Devonian plants. The plant consists of branched axes exhibiting a similar distinctive cortex pattern, xylem shape, and mode of lateral trace departure with some axes showing only primary xylem and some secondary xylem (wood). These features and details about lateral trace departure support establishing a new basal cuphyllophte taxon, Doperyia elongata gen, et sp. nov., adding to the known diversity of small Early Devonian plants with secondary growth. Methodology. Adpressions of axes were prepared by d & eacute;gaging. Localized regions of permineralization on axes and nodules in the adjacent matrix were removed, embedded, and sectioned. Sections were polished, etched and mounted on slides, and then examined with LM, SEM, and micro-computed tomography scanning Pivotal results. Ribbed axis fragments of D. elongata exhibit anisotomously dividing main axes with or without secondary xylem and isotomously divided lateral axes. Larger axes have a variably thick sclerenchyma-tous outer cortex, and smaller axes have less so. Lateral traces depart singly from either end of the elongate haplostele and then divide, producing two clongate-ovoid xylem strands. In axes with secondary xylem, only carly stages of lateral trace departure are known. All tracheids exhibit scalariform-bordered pitting with multi-perforate apertures (P-type). Conclusions. These remains represent a single Early Devonian cuphyllophyte taxon, named D. elongata, presenting information on the presence or absence of secondary xylem in an Early Devonian plant and details of lateral trace departure. These fossils demonstrate that similar-appearing, anisotomously branched, ribbed axes are a feature of several cuphyllophyte genera that possess different internal anatomy. Anatomical changes from the main to the lateral axis indicate a more pseudomonopodial architecture than inferred from external morphol ogy. Secondary xylem features support a mosaic expression of regulatory modules, as suggested for other Early Devonian woody plants.
Premise of research. Fossil fruits and seeds assignable to Herendeeniodoxa willistonensis Pigg, Ickert-Bond, DeVore & Flynn gen. et sp. nov. (Actinidiaceae) are described from the Late Paleocene (Tiffanian) Almont and Beicegel Creek localities in the Williston Basin, North Dakota, USA. Methodology. Fossil fruits and seeds occurring in silicified shale with external morphology were studied with reflected LM. Some specimens with detailed anatomical preservation were prepared by the cellulose acetate peel technique as modified for hydrofluoric acid, mounted on microscope slides, and digitally imaged with transmit ted light. The holotype specimen and an isolated seed were studied with CT scanning. Extant fruits were imaged and prepared by free-hand sectioning with a razor blade, and others were prepared by standard techniques and studied with transmitted LM. Pivotal results. Based on fruit and seed morphology and anatomy, Herendeeniodoxa is assignable to Acti nidiaceae but has a mosaic combination of features not found in extant genera of this family. General fruit shape and organization resemble those of Saurauia and Clematoclethra; however, seed morphology and seed coat anatomy are more like those of Actinidia, and seed coat anatomy also resembles that of Clematoclethra. This suggests that Herendeeniodoxa represents a mosaic taxon prior to, or during, the modern diversification of Actinidiaceae. Conclusions. Herendeeniodoxa willistonensis is the first fruit of Actinidiaceae to be recognized in the Late Paleocene of the Western Interior of North America. Herendeeniodoxa willistonensis provides information about fruits and anatomical seed structure for a group previously known mainly from its distinctive seed casts and compressions. The record suggests a North American/European origin for Actinidiaceae, as well as further early di versification into western North America in the Paleogene, then in Europe from the Eocene onward. The family appears in Asia by the Miocene. The current distribution is in Asia for Actinidia and Clematoclethra, whereas Saurauia is more widely distributed in tropical Asia, Oceania, and the Neotropics.
Premise of research. Tree ferns with an arborescent habit were diverse and ecologically significant throughout the Mesozoic; however, many taxa remain poorly understood as a result of their enigmatic morphologies and a sparse fossil record, particularly from northwestern Gondwana. Establishing their systematic affinities and evolutionary relationships is crucial to understanding Mesozoic forest ecology and fern evolution. Methodology. The new fossil material comes from deposits of Early Cretaceous (late Aptian) age in Colombia. The permineralized fossil was analyzed using thin sections and acetate peels. Phylogenetic and morphospace analyses were conducted to assess relationships and morphological similarities among Paradoxopteris, Alstaettia, Palmoidopteris, and Weichselia based on stem morphology and anatomy. Pivotal results. Paradoxopteris huertasii sp. nov. is distinguished by unique anatomical features including parallel meristeles and auxiliary strands. Phylogenetic and morphospace analyses support a potential "paradoxopterid" clade comprising Paradoxopteris and Weichselia. This hypothesis reinforces the recommendation to retain separate genus designations for foliage (Weichselia) and stem (Paradoxopteris) remains. Conclusion. Paradoxopteris huertasii provides critical anatomical data that advance understanding of paradoxopterid ferns and their evolutionary relationships. Resolving their affinities will require comprehensive anatomical study, reevaluation of historical specimens, and whole-plant reconstructions to clarify the diversity and systematics of Mesozoic tree ferns.
Premise of research. The cladoxylopsids s.l. are an extinct group famous for including taxa that formed the first forests during the Middle Devonian. While different growth models have been proposed for the largest cladoxylopsids, similar analyses have never been conducted on smaller representatives of the group. Here, we propose the first architectural reconstruction of a nonarborescent cladoxylopsid, based on Cladoxylon taeniatum specimens from the early Carboniferous of France. Methodology. About 200 thin sections, wafers, and peels corresponding to 53 anatomically preserved specimens of Cladoxylon from the Tournaisian Lydiennes Formation were observed to describe their anatomy and trace emission patterns. Variations in stele anatomy within the most common morphotype were also studied using principal component analysis and hierarchical clustering. Pivotal results . Four stele morphotypes are recognized based on differences in stele shape, diameter (6.5-30 mm), and secondary growth. One morphotype is assigned to Cladoxylon mirabile and the three others to C. taeniatum. Cladoxylon taeniatum specimens are reconstructed as stems that bore petiole-like organs with dichotomous ultimate appendages. Variations in stele anatomy among the C. taeniatum specimens, combined with previous knowledge on cladoxylopsids growth, suggest an apoxogenetic growth and a determinate development of the secondary xylem for these stems. Two hypotheses on the likely architecture of the whole plant are presented. Conclusions. This study provides the first reconstruction of the development, organotaxis, and possible habit of C. taeniatum, which advances our understanding of the architecture of nonarborescent cladoxylopsids.
Premise of research. Polyploidy can alter plant phenotypes and may enhance the ability of plants to take advantage of high soil nutrient concentrations in their environment or exhibit tolerance to saline conditions. Experimental studies are useful to test how polyploid and diploid plants differ in their growth and reproductive success in different soil nutrient and saline conditions. Methodology. Here, we used growth chambers and reciprocal transplants in field habitats to test whether different soil nutrient-supplemented (nitrogen [N] and phosphorus [P]) and saline (NaCl) conditions and natural field soil conditions affected the number of leaves and flowers, size of longest leaves, relative growth rate, reproductive output, and survival of diploid and tetraploid individuals of Rhodohypoxis baurii var. platypetala. Pivotal results. Tetraploidy was not associated with an increase in the number of leaves and flowers, size of longest leaves, and relative growth rate and increased reproductive output under N or P enrichment in growth chambers and did not increase survival rate under NaCl. Reciprocal transplants showed a similar survivorship and reproductive output between diploid and tetraploid individuals, suggesting that the different ploidies are capable of establishing in each other's environment. Conclusions. Together, findings from this study indicate that polyploidy in R. baurii var. platypetala does not necessarily confer a growth or reproductive advantage or limitation under different soil nutrient levels in the growth chambers or in the field.
Premise of research. Hermaphroditic flowers are occasionally reported in dioecious willows (Salix spp.). We were interested in whether these flowers increased or decreased reproductive potential. Methodology. We compared components of the reproductive potential of eight rare leaky hermaphrodite trees, 22 male trees, and 22 female trees within a hybrid population of Salix nigra # S. gooddingii, located in Dickens County, Texas. Reproductive traits, including the number of ovules per ovary, anthers per flower, catkins per branch, flowers per catkin, pollinator visitation, and days to germination, were measured and compared among bisexual flowers and catkins from leaky hermaphrodites, staminate flowers from male trees, and pistillate flowers from female trees. Pivotal results. Bisexual flowers on leaky hermaphrodites exhibited significantly reduced reproductive poten tial when compared to unisexual flowers from males and females, with fewer ovules and anthers per flower and fewer flowers per catkin, suggesting reduced overall fitness. A significant interaction was detected between sexual phenotype and observation day; for the unisexuals, insect visitation was notably higher during the first observation day than the second observation day. Days to seed germination were not significantly different across floral pheno types. We found a significant negative correlation between ovules per ovary and anthers per flower in bisexual f lowers, which suggested a trade-off in resource allocation at the flower level that could contribute to the mainte nance of dioecy in this population. Conclusions. Our study suggests that hermaphrodites are unlikely to spread within the population, sup porting dioecy as an evolutionarily stable strategy for willows.
Premise of study. Davidia involucrata Baill. (Nyssaceae) is considered a "living fossil" species, with a natural distribution in the mountains of southwestern and central China presently, but its historical distribution is still unclear because of limited fossil records. This study reported Davidia endocarp fossils in appreciable numbers from the early Eocene (similar to 55-52 Ma) sedimentary sequence of India, comprising the first fossil record of this genus in South Asia. Methodology. We determined the studied fossils' taxonomic position based on their detailed morphological features in comparison to modern and fossil endocarps of Cornales. The paleoclimate conditions of Davidia were quantitatively reconstructed using the coexistence approach. Pivotal results. These fossil specimens, characterized by vertically and laterally compressed ellipsoid to obovoid endocarps; five to eight prominent, external, longitudinal, and meridianal ribs; five to seven elliptical locules; and the presence of fibers at the inner endocarp wall, are described as a new species, namely, Davidia indica A. Ali, T. Su et M. A. Khan sp. nov. Conclusions. This discovery supports the close biogeographic lineage between India and other parts of the Northern Hemisphere. This discovery suggests that, like other "living fossil" species, Davidia had a much wider ecological niche in the geological past than it has in the present day, emphasizing the need for further studies regarding the factors in shaping its modern restricted distribution.
Premise of research. Polystichum (Dryopteridaceae), the third-largest fern genus in the world, is globally dis tributed, and tropical America is one of its main centers of diversity. Molecular evidence suggests that Polystichum diverged during the Eocene. Tropical America, the Greater Antilles, Mexico, and the northern and central Andes are its centers of diversity. The discovery of a new fossil from the early Pliocene of the Central Andean Plateau (CAP) in Peru provides evidence for understanding the divergence of the Andean lineage. Methodology. The fossil specimen was compared to extant species of Dryopteridaceae and previously documented fossil records through a review of herbarium specimens and literature. To estimate the phylogenetic position of the fossil, we conducted a scaffold phylogenetic analysis using maximum parsimony. The morphological information used in the analysis was gathered in a matrix that contained 30 frond and sporangial characters for 29 taxa, including the fossil under study; 25 extant species of Polystichum; and three outgroups' species. Once placed in the phylogeny, the fossil was formally described. Pivotal results. The scaffold phylogenetic analysis placed the fossil within clade III of exindusiate Andean Polystichum. We described and named the fossil Polystichum espinarensis sp. nov. We revisited the earlier fossil record of Polystichum bolivianum Berry and concluded that its proposed affinity lacks sufficient morphological ev idence. Therefore, P. espinarensis is proposed as the only fossil record known for the genus. Conclusions. This study sheds light on the diversification and biogeographic history of Andean Polystichum, indicating that P. espinarensis was already present in the early Pliocene. Its diversification, particularly among exindusiate Andean Polystichum species, was likely driven by the Pliocene uplift of the CAP.
Premise of study. Although Garcinia (Garcinieae: Clusiaceae) is well represented through vegetative parts (leaves and wood) in the fossil record, no fossil flower that could provide new information on the reproductive structures of this genus had been discovered until now. Here, for the first time, we report and describe fossil flowers in appreciable numbers with affinity to Garcinia L. from the Early Eocene (ca. 55-52 Ma) of Rajasthan, western India. In addition, we introduce a Garcinia-like fossil flower bud and a fruit from the same stratigraphic level. Methodology. We determine their taxonomic position based on detailed comparative morphology and phylogenetic analysis that resulted from a Bayesian combined analysis of molecular and morphological characters of the modern members of Clusiaceae. Pivotal results. The Eocene flower specimens are characterized by a long pedicellate with a perianth of four preserved petals, a superior and stipitate ovary, and the presence of numerous long staminal filaments arising from the base of the ovary, and a single style is recognized as a new genus and species named Eogarcinia longistaminata A. Ali, R. F. Almeida & M. A. Khan gen. et sp. nov. Conclusions. This finding constitutes the oldest reliably identified reproductive structures of Garcinia from the Cenozoic strata elsewhere. This discovery provides support for the hypothesis of Gondwanan origin and early diversification of Garcinia within the Indian subcontinent during its northward tectonic drift. It also offers new insights into the floral evolutionary trajectory, paleoclimate, and paleobiogeography of Garcinia.
Premise of research. Shifts between climbing and self-supporting forms drive modifications in wood and bark anatomy, reflecting mechanical and physiological adaptations. The Bunchosia clade (Malpighiaceae) offers an ideal model to examine these changes, as evidence suggests independent transitions to self-supporting forms from a lianescent ancestor. This study examines how vascular traits differ between climbers and self-supporting species, explores their evolutionary history, and identifies the developmental mechanisms that have shaped these anatomical traits over time. Methodology. We analyzed 24 Malpighiaceae species, including 19 from the Bunchosia clade, collecting stem samples for anatomical analysis. We examined 23 anatomical traits (18 discrete, five continuous), reconstructed their evolution using a calibrated phylogeny, estimated ancestral states, and tested correlations between habit and some vascular traits through stochastic mapping and phylogenetic comparative methods. Pivotal results. The ancestral condition in the Bunchosia clade likely featured diffuse porous wood, vessel dimorphism, narrow rays, septate fibers, and biphasic development. In lianas, these traits were maintained but with further evolution of wider vessels, high vessel frequency, gelatinous fibers, and mixed heterocellular rays appearing. In contrast, self-supporting species lost biphasic development, reduced vessel frequency, and evolved narrower vessels with abundant axial parenchyma. Vessel dimorphism was maintained in most genera except the self-supporting Bunchosia. In bark, the sieve tube area decreased in self-supporting species and increased in lianas. Conclusions. The study shows that the Bunchosia clade has anatomical differences between lianas and self-supporting species. These differences highlight adaptations to climbing or self-supporting habits, with anatomical evolution involving heterochronic (paedomorphic) and homeotic shifts, offering insight into vascular diversification in Malpighiaceae. These findings highlight the deep connection between plant developmental processes and the interaction between their morphological structures and the vascular system. Moreover, these mechanisms enable plants to adapt to environmental conditions, underscoring the importance of understanding their evolution in explaining their diversity and ability to thrive in various ecosystems.
The gametangia are critical organs of the land plant gametophyte that form, house, and disperse the gametes. Because of their biological importance, gametangium structure tends to be highly conserved within lineages, yet they still exhibit marked morphological differences between the major lineages. The morphology and development of land plant gametangia have been studied for over 150 years, yet significant questions remain about their evolutionary origin, homologies between them, and how they are patterned by the genome. We synthesize existing knowledge about the developmental patterning of land plant gametangia into a single shared framework that identifies homologies across lineages, allowing new conclusions and insights to be garnered. We then combine this framework with a review of what little is currently known about gene pathways recognized to pattern gametangia. The genomic tools and resources needed to complete our understanding of land plant gametangium patterning are now available, and we highlight key directions for future research through testable hypotheses identified in this work.
Premise of research. Seed dormancy is one of the main mechanisms controlling germination timing, particularly in species that fruit late in the rainy season. However, a less understood and alternative strategy involves a fine-tuning of germination with strict environmental requirements. Here, we hypothesized that temperature and soil water availability can control the germination timing of Miconia rubiginosa, a widely distributed Neotropical tree that releases nondormant seeds at the end of the rainy season. Methodology. Germination of M. rubiginosa was examined using a factorial combination of temperatures (20 degrees C, 25 degrees C, and 30 degrees C) and water potentials (0, -0.2, -0.4, -0.6, -0.8, and -1 MPa). Hydrotime-to-event models were applied to calculate germination thresholds at each temperature. Additionally, field data on soil water potential and air temperature were used to predict germination timing over three consecutive years at the same study site. Pivotal results. Germination required higher soil moisture at higher temperatures, with the base water potential increasing from -1.33 MPa at 20 degrees C to -0.4 MPa at 30 degrees C. Miconia rubiginosa also exhibited slow germination, reflected in high hydrotime values (>20 MPa/d). Field-based models predicted two germination windows: one at the end of the rainy season and another at the onset of the following rainy season. Conclusions. Miconia rubiginosa ensures optimal germination for a fraction of its seed population by matching its germination requirements with the seasonal environment. This strategy provides an effective alternative to dormancy and may contribute to the species' broad distribution range by enabling successful germination in diverse environmental conditions while avoiding the ecological costs associated with dormancy.
