Figure 2 - available via license: Creative Commons Attribution 4.0 International
Content may be subject to copyright.
SRXTM volume renderings of flower bud of Caliciflora mauldinensis gen. et sp. nov. from the Late Cretaceous (earliest Cenomanian) Mauldin Mountain locality, MD, USA; holotype (PP53985; sample Mauldin Mountain 116). (a) Volume rendering of apical view of entire floral bud showing subtending bract (br), prophylls (pp) and five revolute-valvate sepals (s). (b-g) Transverse views of flower bud at different levels from apex (b) to middle of floral cup (g) showing subtending bract (br), two prophylls (pp), five revolute-valvate sepals (s), five petals (p), three antesepalous stamens (arrowheads), five antepetalous stamens (asterisks) and three carpels; note three closely appressed stigmas (c) and the free ventral margins of carpels below the stigmatic region ( f,g) (a, not cut; b, section at level of orthoslice xy0766; c, section at level of orthoslice xy1756; d, section at level of orthoslice xy1916; e, section at level of orthoslice xy2044; f, section at level of orthoslice xy2233; g, section at level of orthoslice xy2427). (h,i) Longitudinal views of flower bud in median section showing floral cup surrounding the carpels and with antesepalous stamens (arrowheads) and antepetalous stamens (asterisks) on the rim of the floral cup (h, section at level of orthoslice xz1112; i, section at level of orthoslice yz0983).
Source publication
Eudicots, the most diverse of the three major clades of living angiosperms, are first recognized in the latest Barremian–earliest Aptian. All Early Cretaceous forms appear to be related to species-poor lineages that diverged before the rise of core eudicots, which today comprise more than 70% of angiosperm species. Here, we report the discovery of...
Contexts in source publication
Context 1
... the floral bud, the three stamens that are opposite the sepals (antesepalous) are borne on the rim of the floral cup. Five stamens opposite the petals (antepetalous) are borne below this level ( figure 2c-e,h,i). Anthers are tetra- sporangiate, dithecal and dorsifixed (figure 4a,h). ...
Context 2
... three free carpels (figures 2c-i and 4a,h) are borne on the inside of the floral cup above the free space of the floral apex. In the flower bud, the carpels are fully open along the ventral suture below the stigmatic region ( figure 2c-g). In this specimen, no ovules are developed and there is no indication of placentation. ...
Citations
... The similar subclasses composition and genome-wide proportion of papaya and typical eudicots revealed that the papaya NLR family is a simplified set of NLRs in typical eudicots. The study of papaya NLRs will help us better understand the complex and diverse disease-resistance genes in eudicots, which comprise the largest species diversity of living angiosperms [67,68]. ...
Carica papaya maintains an abnormally small but complete NLR family while showing weak disease resistance. To better understand their origin, evolution, and biological function, we identified 59 NLR genes via a customized RGAugury and investigated their characteristics, evolutionary history, and expression profiles based on the improved papaya genome and large-scale RNA-seq data. The results indicated that duplication is a major evolutionary force driving the formation of the papaya NLR family. Synteny analyses of papaya and other angiosperms showed that both insertion and inheritance-derived NLRs are present in papaya. Transcriptome-based expression and network analyses revealed that NLRs are actively involved in biotic stress responses. For example, a papaya-specific inserted TNL was up-regulated strongly by the fungal infection. Both transcriptome and qRT-PCR analyses confirmed the expression divergence of an RNL and an RCNL, a pair of tandem duplication genes involved in different co-expression modules. Furthermore, we observed an inserted gene cluster composed of five duplicated CNLs, showing dosage effects and functional differentiation of disease-resistance genes during evolution. This research will enhance our knowledge of the special NLR family in papaya, which may serve as a model plant for disease-resistance genetic studies.
... Polyploidization events, such as tetraploidization (whole-genome duplication, WGD) and hexaploidization (whole-genome triplication, WGT), occur frequently in plants and are a major source of evolutionary change that enables rapid adaptation to different environments [11][12][13][14][15]. Previously, the analysis of core eudicot genomes has revealed a common WGT event that has been designated the γ event [16][17][18]. However, this γ event was not found in Nelumbo nucifera (Proteales) [19,20] or Tetracentron sinense (Trochodendrales) [21,22]. ...
... The total length of the chromosomes was 619. 18 Mb, and they contained ~97.16% of the assembled sequences (Additional file 1: Fig. S3 and Table S4). We then assessed the quality of the B. austro-yunnanensis genome, which revealed that over 98.72% of the Illumina short reads could be mapped to the assembly. ...
Background
Eudicots are the most diverse group of flowering plants that compromise five well-defined lineages: core eudicots, Ranunculales, Proteales, Trochodendrales, and Buxales. However, the phylogenetic relationships between these five lineages and their chromosomal evolutions remain unclear, and a lack of high-quality genome analyses for Buxales has hindered many efforts to address this knowledge gap.
Results
Here, we present a high-quality chromosome-level genome of Buxus austro-yunnanensis (Buxales). Our phylogenomic analyses revealed that Buxales and Trochodendrales are genetically similar and classified as sisters. Additionally, both are sisters to the core eudicots, while Ranunculales was found to be the first lineage to diverge from these groups. Incomplete lineage sorting and hybridization were identified as the main contributors to phylogenetic discordance (34.33%) between the lineages. In fact, B. austro-yunnanensis underwent only one whole-genome duplication event, and collinear gene phylogeny analyses suggested that separate independent polyploidizations occurred in the five eudicot lineages. Using representative genomes from these five lineages, we reconstructed the ancestral eudicot karyotype (AEK) and generated a nearly gapless karyotype projection for each eudicot species. Within core eudicots, we recovered one common chromosome fusion event in asterids and malvids, respectively. Further, we also found that the previously reported fused AEKs in Aquilegia (Ranunculales) and Vitis (core eudicots) have different fusion positions, which indicates that these two species have different karyotype evolution histories.
Conclusions
Based on our phylogenomic and karyotype evolution analyses, we revealed the likely relationships and evolutionary histories of early eudicots. Ultimately, our study expands genomic resources for early-diverging eudicots.
... Therefore, morphological characters have become the only option for phylogenetic analyses of fossil plants. The widespread applications of scanning electron microscopy and synchrotron radiation X-ray tomographic microscopy in fossil taxa have enabled paleobotanists to obtain numerous accurate morphological data from fossils [70]. In contrast, these new techniques are rarely used in studies of extant plant species. ...
Phylogenetics has become a powerful tool in many areas of biology. Land plants are the most important primary producers of terrestrial ecosystems and have colonized various habitats on Earth. In the past two decades, tremendous progress has been made in our understanding of phylogenetic relationships at all taxonomic levels across all land plant groups by employing DNA sequence data. Here, we review the progress made in large-scale phylogenetic reconstructions of land plants and assess the current situation of phylogenetic studies of land plants. We then emphasize directions for future study. At present, the phylogenetic framework of land plants at the order and familial levels has been well built. Problematic deep-level relationships within land plants have also been well resolved by phylogenomic analyses. We pointed out five major aspects of molecular phylogenetics of land plants, which are nowadays being studied and will continue to be goals moving forward. These five aspects include: (1) constructing the genus- and species-level phylogenies for land plant groups, (2) updating the classification systems by combining morphological and molecular data, (3) integrating fossil taxa into phylogenies derived from living taxa, (4) resolving deep-level and/or rapidly divergent phylogenetic relationships using phylogenomic data, and (5) building big trees using the supermatrix method. We hope that this review paper will promote the development of plant molecular phylogenetics and other related areas.
... In angiosperms, gene duplication occurred after the divergence of Amborella trichopoda and monocots, but prior to the divergence of the basal eudicot Nelumbo nucifera, estimated at 100 Ma (Angiosperm Phylogeny website: http://www.mobot.org/ MOBOT/research/APweb/; Friis et al. 2016). This duplication gave rise to the αKNL2 and βKNL2 genes of Arabidopsis and their orthologs in other eudicots. ...
KINETOCHORE NULL2 (KNL2) plays key role in the recognition of centromeres and new CENH3 deposition. To gain insight into the origin and diversification of the KNL2 gene, we reconstructed its evolutionary history in the plant kingdom. Our results indicate that the KNL2 gene in plants underwent three independent ancient duplications in ferns, grasses and eudicots. Additionally, we demonstrated that previously unclassified KNL2 genes could be divided into two clades αKNL2 and βKNL2 in eudicots and γKNL2 and δKNL2 in grasses, respectively. KNL2s of all clades encode the conserved SANTA domain, but only the αKNL2 and γKNL2 groups additionally encode the CENPC-k motif. In the more numerous eudicot sequences, signatures of positive selection were found in both αKNL2 and βKNL2 clades, suggesting recent or ongoing adaptation. The confirmed centromeric localization of βKNL2 and mutant analysis suggests that it participates in loading of new CENH3, similarly to αKNL2. A high rate of seed abortion was found in heterozygous βKNL2 plants and the germinated homozygous mutants did not develop beyond the seedling stage. Taken together, our study provides a new understanding of the evolutionary diversification of the plant kinetochore assembly gene KNL2, and suggests that the plant-specific duplicated KNL2 genes are involved in centromere and/or kinetochore assembly for preserving genome stability.
... Investigations of small coalified and charcoalified flowers, fruits and seeds from Cretaceous strata, combined with information from fossil leaves as well as extensive palynological data, document a massive and rapid diversification of eudicots, beginning in the late Barremianearly Aptian and continuing through the Albian into the Late Cretaceous (e.g., Doyle and Hickey 1976, Hickey and Doyle 1977, Crane and Lidgard 1989, Crane et al. 1995, Friis et al. 2006a, Herendeen et al. 2017. Central in this diversification is the expansion and diversification of core eudicots (Crepet 1996, Magallón et al. 1999, Crepet et al. 2004, Friis et al. 2006a, b, 2011, 2016. Of the two major groups of core eudicots, rosids are well-represented in Late Cretaceous fossil flower and fruit assemblages by early forms of uncertain relationship (Friis et al. 2016) as well as early Fabales (Manchester et al. 2018), and also by species belonging to extant Fagales, including the diverse and widespread Normapolles group, a complex of extinct plants related to Betulaceae-Casuarinaceae-Ticodendraceae and Juglandaceae-Myricaceae-Rhoipteleaceae (Friis 1983, Knobloch and Mai 1986, Sims et al. 1999, Friis et al. 2003, 2006b. ...
... Central in this diversification is the expansion and diversification of core eudicots (Crepet 1996, Magallón et al. 1999, Crepet et al. 2004, Friis et al. 2006a, b, 2011, 2016. Of the two major groups of core eudicots, rosids are well-represented in Late Cretaceous fossil flower and fruit assemblages by early forms of uncertain relationship (Friis et al. 2016) as well as early Fabales (Manchester et al. 2018), and also by species belonging to extant Fagales, including the diverse and widespread Normapolles group, a complex of extinct plants related to Betulaceae-Casuarinaceae-Ticodendraceae and Juglandaceae-Myricaceae-Rhoipteleaceae (Friis 1983, Knobloch and Mai 1986, Sims et al. 1999, Friis et al. 2003, 2006b. Asterids are also well-represented among fossil flowers and fruits from the Late Cretaceous, but are mainly restricted to Cornales and Ericales, two clades that appear to have diverged early from other asterids. ...
A distinctive feature of the major eudicot diversification that occurred through the Late Cretaceous is the unequivocal presence of Cornales and diverse Ericales. Here we describe well-preserved fossil flowers from the Mira locality in western Portugal, of Campanian-Maastrichtian age, that we assign to a new extinct genus of Ericales with two new species; Miranthus elegans gen. et sp. nov. and Miranthus kvacekii sp. nov. The fossil flowers are pedicellate, structurally bisexual, actinomorphic, pentamerous and isomerous, with five narrowly triangular persistent calyx lobes, a five-lobed corolla, five antepetalous stamens, five staminodes alternating with the petals and a semi-inferior, unilocular ovary. The ovary consists of five carpels and has a raised nectariferous ring with stomata-like openings above the insertion of the perianth, and a long five-angled style. A key feature, which confirms a relationship with Primulaceae s. l., is the free, central dome-shaped placenta that bears numerous, densely spaced ovules. The ovary matures into a capsule containing many, minute, reticulate seeds. Flowers of Miranthus are especially similar to those of extant Samolus, a genus of about twelve species that is sister group to other genera of subfamily Theophrastoideae and that has a disjunct distribution mainly in the Southern Hemisphere. Miranthus also appears to have grown in environments influenced by marine conditions, an ecological preference also seen in Samolus. Miranthus expands the diversity of Ericales known from the Late Cretaceous, and together with previously described fossils provides further evidence that the diversification of Ericales was already underway by the Campanian-Maastrichtian stages of the Late Cretaceous.
... Our findings reveal the hybrid structure of core eudicot genomes and will hopefully help us understand what hybridization has meant for core eudicots-a group which comprises more than 70% of all living flowering plants [55]. What are the hybridization-coupled changes that have led to the current patterns of gene expression, methylation, or transposable element density/distribution? All these questions call for additional genomes from basal eudicots which-as this study illustrateshave great values as outgroup to the core eudicots. ...
Background:
Whole-genome duplications (WGDs) have dominated the evolutionary history of plants. One consequence of WGD is a dramatic restructuring of the genome as it undergoes diploidization, a process under which deletions and rearrangements of various sizes scramble the genetic material, leading to a repacking of the genome and eventual return to diploidy. Here, we investigate the history of WGD in the columbine genus Aquilegia, a basal eudicot, and use it to illuminate the origins of the core eudicots.
Results:
Within-genome synteny confirms that columbines are ancient tetraploids, and comparison with the grape genome reveals that this tetraploidy appears to be shared with the core eudicots. Thus, the ancient gamma hexaploidy found in all core eudicots must have involved a two-step process: first, tetraploidy in the ancestry of all eudicots, then hexaploidy in the ancestry of core eudicots. Furthermore, the precise pattern of synteny sharing suggests that the latter involved allopolyploidization and that core eudicots thus have a hybrid origin.
Conclusions:
Novel analyses of synteny sharing together with the well-preserved structure of the columbine genome reveal that the gamma hexaploidy at the root of core eudicots is likely a result of hybridization between a tetraploid and a diploid species.
... Determining the exact botanical affi nities of three-dimensional objects (fl owers, seeds, and fruits) is challenging, because internal structures may not be accessible using standard nondestructive methods such as light microscopy. During recent years, a new powerful nondestructive method, synchrotron-radiation-based X-ray micro-computed tomography (SRμCT), has increasingly been applied in the study of three-dimensionally preserved paleontological objects (Friis et al., 2016 ). SRμCT has also been used for arthropod inclusions in amber to visualize and digitally dissect inclusions without destroying valuable specimens (Stebner et al., 2016 ). ...
Premise of the study:
The Eocene Baltic amber deposit represents the largest accumulation of fossil resin worldwide, and hundreds of thousands of entrapped arthropods have been recovered. Although Baltic amber preserves delicate plant structures in high fidelity, angiosperms of the "Baltic amber forest" remain poorly studied. We describe a pistillate partial inflorescence of Castanopsis (Fagaceae), expanding the knowledge of Fagaceae diversity from Baltic amber.
Methods:
The amber specimen was investigated using light microscopy and synchrotron-radiation-based X-ray micro-computed tomography (SRμCT).
Key results:
The partial inflorescence is a cymule, consisting of an involucre of scales that surround all four pistillate flowers, indicating a dichasium cupule. Subtending bracts are basally covered with peltate trichomes. Flowers possess an urecolate perianth of six nearly free lobes, 12 staminodia hidden by the perianth, and a tri-locular ovary that is convex-triangular in cross section. The exceptional three-dimensional preservation suggests that the fossil belongs to the extant East Asian genus Castanopsis. The amber inclusion represents the first record of Castanopsis from Baltic amber and the first pistillate inflorescence of Fagaceae from Eurasia.
Conclusions:
The partial female inflorescence reported here provides an important addition to acorns of Castanopsis described from middle Eocene strata of Europe. Furthermore, the intercontinental distribution of Castanopsis in the Eocene is confirmed. The amber fossil also broadens the picture of the Baltic amber source area, indicating oligotrophic, sandy, bog-like habitats. Finally, this study underscores the great benefit of SRμCT as a powerful tool to investigate plant inclusions from amber in a nondestructive way.
... Exceptionally well-preserved fossils recently recovered from Upper Cretaceous deposits (~100-66 Ma) have provided mean- ingful advancements in our understanding of the initial diversifi- cation of major core eudicot clades, the asterids and rosids (e.g. Friis et al., 2011Friis et al., , 2016Atkinson, 2016Atkinson, , 2018Martínez et al., 2016;Atkinson et al., 2018). The earliest known core eudicots are rosid flowers and infructescences from the middle Cretaceous (~100 Ma) of North America ( Basinger and Dilcher, 1984;Friis et al., 2016;Manchester et al., 2018). ...
... Friis et al., 2011Friis et al., , 2016Atkinson, 2016Atkinson, , 2018Martínez et al., 2016;Atkinson et al., 2018). The earliest known core eudicots are rosid flowers and infructescences from the middle Cretaceous (~100 Ma) of North America ( Basinger and Dilcher, 1984;Friis et al., 2016;Manchester et al., 2018). Asterids appear relatively late in the fossil record, near the Turonian-Coniacian boundary (~90-89 Ma) (Takahashi et al., 2002;Martínez-Millán, 2010;Friis et al., 2011;Manchester et al., 2015;Atkinson et al., 2018), indicating that the initial phase of core eudicot evolution was dominated by rosid taxa; however, this pattern could be due to reporting and sampling biases. ...
... Recently characterized well-preserved Cretaceous fossils, such as E. jerseyensis, are contributing much needed information on the initial diversifica- tion of core eudicots (e.g. Martínez et al., 2016;Friis, et al., 2016;Atkinson et al., 2018). ...
Background and aims
The asterids (>80 000 extant species) appear in the fossil record with considerable diversity near the Turonian–Coniacian boundary (~90 Ma; Late Cretaceous) and are strongly represented in the earliest diverging lineage, Cornales. These early asterid representatives have so far been reported from western North America and eastern Asia. In this study, we characterize a new cornalean taxon based on charcoalified fruits from the upper Turonian of eastern North America, a separate landmass from western North America at the time, and identify early palaeobiogeographical patterns of Cornales during the Cretaceous.
Methods
Fossils were studied and imaged using scanning electron microscopy and micro-computed tomography (micro-CT) scanning. To assess the systematic affinities of the fossils, phylogenetic analyses were conducted using maximum parsimony.
Key results
The charcoalified fruits are represented by tri-locular woody endocarps with dorsal apically opening germination valves. Three septa intersect to form a robust central axis. Endocarp ground tissue consists of two zones: an outer endocarp composed of isodiametric sclereids and an inner endocarp containing circum-locular fibres. Central vasculature is absent; however, there are several small vascular bundles scattered within the septa. Phylogenetic analysis places the new taxon within the extinct genus Eydeia.
Discussion
Thick-walled endocarps with apically opening germination valves, no central vascular bundle and one seed per locule are indicative of the order Cornales. Comparative analysis suggests that the fossils represent a new species, Eydeia jerseyensis sp. nov. This new taxon is the first evidence of Cornales in eastern North America during the Cretaceous and provides insights into the palaeobiogeography and initial diversification of the order.
... Recently, another genus of flower with Rosid Clade affinties, Caliciflora, was recognized from sediments of slightly younger age from the Potomac Group of northeastern Maryland (Friis et al. 2016). Like Dakotanthus, Caliciflora has five sepals and five petals, but it has only eight anthers and three free carpels. ...
An extinct plant that populated the eastern margin of the Cretaceous Midcontinental Seaway of
North America about 100 million years ago has attracted interest as one of the earliest known bisexual flowers
in the fossil record. Reexamination of the type specimen of Carpites cordiformis Lesq., and corresponding specimens
from sandstones and clays of the Dakota Formation of Kansas and Nebraska and the correlative Woodbine
Sandstone of Texas, with both light microscopy and micro CT scanning, leads to a revised concept of the morphology
and affinities of the “Rose Creek flower”. The moderately large flowers (22–30 mm diameter) have two
perianth whorls: five basally fused sepals and five free spatulate petals. The gynoecium is pentacarpellate with
five styles. A crescent-shaped nectariferous pad occurs at the base of the gynoecium aligned with each sepal. Ten
stamens are inserted at the level of the nectaries, one whorl organized opposite the sepals and another opposite
the petals. In situ pollen is oblate, brevitricolporate and finely verrucate. The fruits are loculicidal capsules with
persistent calyx and disk. Comparing the full suite of observed characters with those of extant angiosperms
indicates particularly close similarity to the monogeneric fabalean family Quillajaceae, with shared features
of perianth number and morphology, nectary position and morphology, stamen number and morphology, and
gynoecium merosity, although the fossil differs from extant Quillaja in fruit type (capsule vs basally syncarpous
follicles) and especially in pollen morphology (10 μm oblate, microverrucate, vs 30–40 μm prolate, striate).
... The Late Cretaceous was a remarkable time interval in the history of angiosperm evolution because during that interval they underwent significant diversification resulting in the appearance of the majority of the angiosperm clades known today (Crepet et al., 2004;Friis et al., 2016). Specifically by the last stage of the Cretaceous, the Maastrichtian (72.1e66 million years ago), the angiosperms were the most species rich group compared to other plant lineages. ...
