Orthotropous Ovules Research Articles

A novel cupulate seed plant, Xadzigacalix quatsinoensis gen. et sp. nov., provides new insight into the Mesozoic radiation of gymnosperms.

PremiseAnatomically preserved evidence for a novel clade of gymnosperms emphasizes diversity of seed plants immediately prior to the appearance of angiosperm fossils in the paleontological record.MethodsCupulate seeds from the Early Cretaceous Apple Bay locality (Vancouver Island) are described from serial cellulose acetate peels and three‐dimensional reconstruction. Phylogenetic context is assessed through the comparative analysis of gymnosperm seed producing fructifications and maximum parsimony analysis of a revised morphological data set for seed plant phylogeny.Results Xadzigacalix quatsinoensis gen. et sp. nov. is characterized by an orthotropous ovule with an elongated micropyle and complex integument, enclosed within a radial cupule. The micropylar canal is elongated; and the nucellus extends into the micropyle to seal the post pollination ovule. Except at the apex of the micropyle, the seed is completely enclosed by a parenchymatous cupule with ca. 20 axially elongated secretory ducts. The cupulate seed is produced upon a triangular woody stele, consisting of a parenchymatous pith surrounded by radially aligned tracheids. The stele produces three short terete traces that terminate within the base of the cupule as transfusion tissue at the seed chalaza.ConclusionsOrganography, vascularization, nature of the integument and nucellus, and configuration of the micropylar canal distinguish Xadzigacalix quatsinoensis from all other gymnosperm clades. Cladistic analyses suggest the new plant may have affinities with gnetophytes or angiosperms. These results are complemented with a critical re‐evaluation of ovulate structures for Mesozoic gymnosperms, providing new insight into plant diversity immediately antecedent to the explosive diversification of flowering plants.

An edible fruit from the Jurassic of China

ABSTRACT Frugivory is an important ecological tie between animals and angiosperms. It plays an important role in the evolution of food webs and energy flow networks in the ecosystem. However, little is known about how old this relationship can be due to lack of relevant fossil evidence. Here, the authors report a fossil fruit, Jurafructus gen. nov., a putative angiosperm from the Middle–Late Jurassic (>164 Ma) of Daohugou Village, Inner Mongolia, China, which provides the currently earliest evidence of frugivory. The fossil is a more or less three-dimensionally preserved coalified drupe that has been damaged by animals in two different ways. The pericarp, in addition to the seed coat surrounding parenchyma seed contents, is suggestive of an angiospermous affinity, as such a 3+3 structure is distinct from a three-layered seed coat in gymnosperms. The seed possesses a distal micropyle, attached on the base of the pericarp, suggestive of a former orthotropous ovule in the gynoecium. The damaged pericarp of Jurafructus suggests that frugivory can be dated back to the Middle–Late Jurassic. Apparently, the ecological relationship between angiosperms and animals extends deep into the fossil record.

Evidence of Antiherbvore Defense in a Jurassic Fruit

Frugivory and antiherbvore defense are two games played by animals and plants in their arm racing, and they play important roles in the evolution and well-being of the current ecosystem. However, little is known about the history, especially in their early stage, due to lack of related fossil evidence, despite the history of angiosperms has been dated back to the Early Jurassic. Here we report a fossil fruit, Jingwangfructus gen. nov., from the Middle-Late Jurassic (>164 Ma) of Daohugou Village, Inner Mongolia, China, in which the currently earliest evidence of frugivory and antiherbvore defense are identified. The fossil is more or less three dimensionally preserved coalified drupe that has been superficially damaged by different animals in two different ways. The seed coat and pericarp surrounding parenchyma seed content suggest its angiospermous affinity. The seed with a distal micropyle is attached on the base of the former ovary, suggestive of a basal placentation with an orthotropous ovule in the former gynoecium. The occurrence of sclerenchyma in the fleshy pericarp and the damaged pericarp of Jingwangfructus suggests that interaction between the plant and animals has been established by the Late Jurassic. Apparently, the ecological relationship between angiosperms and animals has a history, the length and complexity of which are beyond former assumptions.

Pseudoasterophyllites cretaceusfrom the Cenomanian (Cretaceous) of the Czech Republic: A possible link between Chloranthaceae andCeratophyllum

AbstractPseudoasterophyllites cretaceus from the Cenomanian of Bohemia was recently recognized as an angiosperm by association with stamens containing monosulcate pollen of the Tucanopollis type. New material indicates that the stamens were borne in short spikes, with each stamen subtended by a bract, whereas the carpels were solitary and contained a single pendent, orthotropous ovule. We have investigated the phylogenetic position of Pseudoasterophyllites by including it in a morphological analysis of extant angiosperms using backbone constraint trees that represent the current range of hypotheses on relationships of the five mesangiosperm clades. With a backbone tree in which Chloranthaceae are linked with magnoliids and Ceratophyllum with eudicots, the most parsimonious position of Pseudoasterophyllites is sister to Chloranthaceae, but a sister‐group relationship to Ceratophyllum is only one step less parsimonious. With a backbone tree in which Chloranthaceae and Ceratophyllum form a clade, Pseudoasterophyllites is sister to Ceratophyllum, based on derived features shared with both Chloranthaceae and Ceratophyllum plus solitary female flowers (as in Ceratophyllum). Similar results are obtained when Pseudoasterophyllites is added to the analysis with other fossils inferred to be related to Chloranthaceae and/or Ceratophyllum. If the plants that produced Tucanopollis pollen in the Barremian‐Aptian of Africa–South America are related to Pseudoasterophyllites, these results suggest that Chloranthaceae and Ceratophyllum are relicts of one of the most important early radiations of angiosperms, which included not only colonizers of disturbed terrestrial habitats but also halophytes and aquatics.

Anatomy and Pollination of Cleistogamous Flowers of Benghal Dayflower (Commelina benghalensis)

The anatomy and pollination of subterranean cleistogamous flowers of Benghal dayflower (Commelina benghalensis) is described as a contribution to understanding its reproductive biology. Subterranean stems bear one spathe per node, each enclosing a single cleistogamous flower. Only the three anterior stamens produce functional pollen; the posterior three stamens are staminodes. Tapetum is amoeboid and endothecium is present. The three-carpellate superior ovary bears five dimorphic orthotropous ovules. Nearly mature flowers have straight to somewhat curved styles; at maturity, styles elongate and coil. Our observations indicate that coiled style growth causes rupture of anthers and brings pollen into contact with stigmas. Pollen tubes were observed in styles that had previously undergone coiling, located within mucilaginous secretions of the mature stylar canal. The subterranean cleistogamous flowers of Benghal dayflower and their apparently unique mode of pollination, viewed together with reproductive capacity of its aerial chasmogamous flowers, underscore the complexity and flexibility of the reproductive biology of this noxious weed species.

Development of ovule, fruit and seed ofXyris(Xyridaceae, Poales) and taxonomic considerations

The development of the ovule, fruit and seed of Xyris spp. was studied to assess the embryological characteristics of potential taxonomic usefulness. All of the studied species have (1) orthotropous, bitegmic and tenuinucellate ovules, with a micropyle formed by both the endostoma and exostoma; (2) a cuticle in the ovules and seeds between the nucellus/endosperm and the inner integument and between the inner and outer integuments; (3) helobial, starchy endosperm; (4) a reduced, campanulate and undifferentiated embryo; (5) a seed coat formed by a tanniferous endotegmen, endotesta with thick-walled cells and exotesta with thin-walled cells; and (6) a micropylar operculum formed from inner and outer integuments. The pericarp is composed of a mesocarp with cells containing starch grains and an endocarp and exocarp formed by cells with U-shaped thickened walls. The studied species differ in the embryo sac development, which can be of the Polygonum or Allium type, and in the pericarp, which can have larger cells in either endocarp or exocarp. The Allium-type embryo sac development was observed only in Xyris spp. within Xyridaceae. Xyris also differs from the other genera of Xyridaceae by the presence of orthotropous ovules and a seed coat formed by endotegmen, endotesta and exotesta, in agreement with the division of the family into Xyridoideae and Abolbodoideae. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 177, 619–628.

Floral development of Cardiopteris, with emphasis on gynoecial structure and ovular morphology

AbstractCardiopteris is unique in the expanded Cardiopteridaceae for several distinctive features, including its gynoecial structure and ovular morphology. We studied the floral development of Cardiopteris to clarify floral morphology and document floral development. Cardiopteris has three carpel primordia, which are separate at their tips but congenitally fused at their bases. The synascidiate zone (the fused proximal part) develops into the unilocular ovary; the three discrete carpel apices diverge in development: the apex of the adaxial carpel differentiates into a style and stigma, while the apices of the two lateral‐abaxial carpels elongate and develop into a fleshy appendage only after fertilization. The ovules are attached to the lateral‐abaxial carpels. At anthesis, the ovules are ategmic and orthotropous without funicles (morphologically undifferentiated). Functional differentiation occurs in the three carpels of Cardiopteris: the adaxial one is the site of pollination, while the lateral‐abaxial two produce ovules. The ategmic orthotropous ovule is unusual in Cardiopteridaceae and is an apomorphy of Cardiopteris.

Morphology ofMaundiasupports its isolated phylogenetic position in the early-divergent monocot order Alismatales

According to recent molecular phylogenetic data, the rare Australian endemic Maundia triglochinoides does not form a clade with taxa traditionally classified as members of Juncaginaceae. Therefore, views on the morphological evolution and taxonomy of Alismatales require re-assessment. As the morphology of Maundia is poorly known and some key features have been controversially described in the literature, the flowers, fruits, inflorescence axes and peduncles were studied using light and scanning electron microscopy. Inflorescences are bractless spikes with flowers arranged in trimerous whorls. Except in the inflorescence tip (where the flower groundplan is variable), flowers possess two tepals in transversal-abaxial positions, six stamens in two trimerous whorls and four carpels in median and transversal positions. Fruits are indehiscent. The shared possession of orthotropous ovules supports the molecular phylogenetic placement of Maundia as sister to a large clade including Potamogetonaceae and related families. Maundia and Aponogeton spp. share the same highly unusual floral groundplan, a homoplastic similarity that can be explained by spatial constraints in developing inflorescences. The nucellar coenocyte of Maundia appears to be unique among monocots. As Maundia exhibits a mosaic of features characteristic of other families of tepaloid core Alismatales, its segregation as a separate family is plausible. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 173, 12–45.

Dordrechtites arcanus sp. nov., an Anatomically Preserved Gymnospermous Reproductive Structure from the Middle Triassic of Antarctica

The genus Dordrechtites is an isolated ovulate structure previously described only from South Africa and Australia as impressions. The discovery of compressed and permineralized specimens of this taxon at the base of Mount Falla (uppermost Fremouw Formation) in the central Transantarctic Mountains extends the geographical and geological distribution of the genus and increases the known floral diversity of the Triassic of Antarctica. The first permineralized species, Dordrechtites arcanus, is described using standard acetate peel techniques and includes internal anatomy of an elongate arm that extends over the top of a central cupule containing two elongate, bilaterally symmetrical, orthotropous ovules. An arc-shaped collateral vascular bundle extends from the arm into the top of the cupule, branches, and then extends around the ovule to about halfway down to the micropylar end. The cupule is parenchymatous and includes transfusion tissue with cells that have pitted walls. The sclerotesta of the ovule is up to 200 μm thick, consisting of an outer layer with longitudinally oriented, thick-walled cells and an inner layer one cell thick of rectangular, thick-walled cells. The micropyle is flared at the attenuated tip of the pyramidal cupule. The four previously described species of Dordrechtites have uncertain affinities, and although the morphology and anatomy of this taxon is now known, the affinities within the gymnosperms are still uncertain.

Fossil floral and fruit evidence for the evolution of unusual developmental characters in Fagales

Flowers of many living Fagales exhibit unusual developmental characteristics. At anthesis, ovulate flowers have carpels bearing immature orthotropous ovules. After pollination, the ovules increase in size and become anatropous and the ovary enlarges. Simultaneously, the pollen tubes extend from the stigma to the ovules with several phases of growth and quiescence. Finally, after the first fertilization, the remaining ovules abort, resulting in a single-seeded fruit. Three-dimensionally preserved potentially fagaceous mesofossil flowers from the Campanian of Massachusetts, USA, provide evidence on the evolution of these characters. The fossils share putative synapomorphies with the Fagales (six tepals, mostly inferior, three-carpellate ovary with each locule initially containing two pendant ovules, punctate-rugulate, tricolporate pollen and fruit with a single seed). However, the fossil is bisexual and has nectaries, characters shared with the sister order Cucurbitales, and both lack the fagalean immature orthotropous developmental stage. The fossil shares synapomorphies of an inferior ovary and a single-seeded indehiscent fruit with both living orders and appears to be transitional. Comparison of ontogenetic changes between the fossil and related fagalean taxa suggests independent stepwise changes in development in which some characters of the modern clades were in place at ∼ 75 Myr and others evolved more recently. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 168, 353–376.

Angiosperm ovules: diversity, development, evolution

Ovules as developmental precursors of seeds are organs of central importance in angiosperm flowers and can be traced back in evolution to the earliest seed plants. Angiosperm ovules are diverse in their position in the ovary, nucellus thickness, number and thickness of integuments, degree and direction of curvature, and histological differentiations. There is a large body of literature on this diversity, and various views on its evolution have been proposed over the course of time. Most recently evo-devo studies have been concentrated on molecular developmental genetics in ovules of model plants. The present review provides a synthetic treatment of several aspects of the sporophytic part of ovule diversity, development and evolution, based on extensive research on the vast original literature and on experience from my own comparative studies in a broad range of angiosperm clades. In angiosperms the presence of an outer integument appears to be instrumental for ovule curvature, as indicated from studies on ovule diversity through the major clades of angiosperms, molecular developmental genetics in model species, abnormal ovules in a broad range of angiosperms, and comparison with gymnosperms with curved ovules. Lobation of integuments is not an atavism indicating evolution from telomes, but simply a morphogenetic constraint from the necessity of closure of the micropyle. Ovule shape is partly dependent on locule architecture, which is especially indicated by the occurrence of orthotropous ovules. Some ovule features are even more conservative than earlier assumed and thus of special interest in angiosperm macrosystematics.

Canrightia resinifera gen. et sp. nov., a new extinct angiosperm with Retimonocolpites-type pollen from the Early Cretaceous of Portugal: missing link in the eumagnoliid tree?

Canrightia resinifera gen. et sp. nov. is based on numerous fossils from several Early Cretaceous localities of western Portugal (Arazede, Buarcos, Catefica, Famalicão, Juncal, Vale de Agua, Vila Verde 2). Scanning electron microscopy (SEM) combined with non-destructive synchrotron radiation-based X-ray tomographic microscopy (SRXTM) has revealed critical external and internal features. Flowers are bisexual with a single whorl of tepals, laterally fused to form a hypanthium. The ovary is semi-inferior and syncarpous formed from two to five carpels, each carpel with a single pendant and orthotropous ovule. Ovules are endotestal-endotegmic with a distinct crystalliferous endotesta and an endotegmen that develops into a prominent endothelium. Pollen is of the Retimonocolpites-type with long extended colpus, semi-tectate reticulate pollen wall, homobrochate reticulum and columellate infratectal layer. Canrightia is in many respects similar to the extinct genus Zlatkocarpus, but is distinguished by its syncarpous organisation and up to five ovules per ovary. Pollen characters and many floral features in Canrightia are plesiomorphic indicating a basal position in the angiosperm phylogenetic tree. Comparison with extant and extinct taxa shows that Canrightia belongs to an extinct lineage and character optimisation suggests a position of Canrightia close to the root of the eumagnoliid tree with particular similarities to Chloranthaceae and Piperales.

Reconstructing the ancestral angiosperm flower and its initial specializations

Increasingly robust understanding of angiosperm phylogeny allows more secure reconstruction of the flower in the most recent common ancestor of extant angiosperms and its early evolution. The surprising emergence of several extant and fossil taxa with simple flowers near the base of the angiosperms-Chloranthaceae, Ceratophyllum, Hydatellaceae, and the Early Cretaceous fossil Archaefructus (the last three are water plants)-has brought a new twist to this problem. We evaluate early floral evolution in angiosperms by parsimony optimization of morphological characters on phylogenetic trees derived from morphological and molecular data. Our analyses imply that Ceratophyllum may be related to Chloranthaceae, and Archaefructus to either Hydatellaceae or Ceratophyllum. Inferred ancestral features include more than two whorls (or series) of tepals and stamens, stamens with protruding adaxial or lateral pollen sacs, several free, ascidiate carpels closed by secretion, extended stigma, extragynoecial compitum, and one or several ventral pendent ovule(s). The ancestral state in other characters is equivocal: e.g., bisexual vs. unisexual flowers, whorled vs. spiral floral phyllotaxis, presence vs. absence of tepal differentiation, anatropous vs. orthotropous ovules. Our results indicate that the simple flowers of the newly recognized basal groups are reduced rather than primitively simple.

The Whole and the Parts: Relationships Between Floral Architecture and Floral Organ Shape, and Their Repercussions on the Interpretation of Fragmentary Floral Fossils1

Floral architecture and floral organ shape are interrelated to some extent as can be seen in the diversity of extant angiosperm groups. The shape of fragmentary fossil material, such as single organs, may therefore give hints for the reconstruction of the architecture of a flower. This study is partly a review and partly provides original material and new points of view on organ-architecture interrelationships. Several topics are illustrated with examples: (1) autonomous and imprinted shape, exemplified by cuneate organs, especially stamens; (2) conditions for valvate anther dehiscence; (3) lability in number and shape of reduced organs that have decreased in size and lost their original function; (4) long hairs as filling material of irregular spaces; (5) architectural conditions for the presence of orthotropous ovules; (6) structural differences between exposed and covered organ parts in bud; and (7) sepal aestivation and petal elaboration.

Infructescences from the Cerro del Pueblo Formation (Late Campanian), Coahuila, and El Cien Formation (Oligocene‐Miocene), Baja California Sur, Mexico

Fruits and infructescences of the Cerro del Pueblo and El Cien Formations, Coahuila and Baja California Sur, Mexico, respectively, allow detailed description and comparison of reproductive structures of plants that grew from the Late Cretaceous at least up to the Miocene. Infructescences collected in the Rincón Colorado and Presa San Antonio localities resemble those of some members of Alismatales; they share multiple or aggregate infructescences, with sessile, unilocular, operculate berrylike fruits, that are free from one another in their distal zones and contain a single orthotropous ovule. Nevertheless, they have other characteristics not found in either fossil or extant infructescences, limiting this resemblance. These features include the development of a distal seed crown by integumentary projection, a fruit operculum inserted into the seed crown, and a channel running through the mesocarp from the exposed operculum surface to the proximal end of the fruit. The presence of sclerotized layers in the seed suggests that the reproductive organs are mature. Differences in number of fruits per infructescence, seed form, number of integumentary layers, and cell sizes in the seed and fruit suggest that two related species are represented among the ca. 1283 known infructescences. This suggests that during the Cretaceous diversity within the order was important. The only infructescence collected from the Oligocene‐Miocene El Cien Formation has a morphology that closely resembles that of the Cretaceous material. Even the polyhedric shape of the exocarp cells of the Baja California Sur material is similar to that of the Coahuila material. Unfortunately, this material was not cut for further comparison, but the available data suggest that this lineage lived in northern Mexico until at least the Oligocene‐Miocene.

Ginkgoalean ovulate organs and seeds associated with Baiera furcata-type leaves from the Middle Jurassic of Qinghai Province, China

Ginkgoalean ovulate organs Yimaia, detached seeds and the associated Baiera-type leaves are described from a paper coal at the uppermost part of the Middle Jurassic Shimengou Formation in the northern border of the Qaidam Basin, Qinghai Province, Northwest China. The organ bears a cluster of at least 3 orthotropous ovules at the apex of a peduncle. The seeds (ovules) are sessile, nearly rounded or broadly ovate to oblong, about 7 mm long and 5.7 mm wide, with an obtusely acute, acute or mucronate apex. Despite a general resemblance in gross morphology, the new Yimaia organ is distinguished from other species of the genus in the stomatal structure of the integument. Associated leaf segments of Baiera bear a resemblance to the Yorkshire Middle Jurassic species B. furcata, but are somewhat different in cuticular structure. Selected Mesozoic leaves with well-preserved cuticle and other Baiera type leaves that are known to have been associated with the Yimaia-type ovulate organs from China and other parts of the world are found to be different either in gross morphology and/or in cuticular structure from the present associated leaf segments. Yimaia ovulate organs and vegetative leaves dominantly of the Baiera-type appear to form a regular combination in the Mesozoic ginkgoaleans. They represented a rather small, but coherent plant group (Yimaiaceae) that was widely distributed in the Jurassic of Eurasia.

A new Late Cretaceous ginkgoalean reproductive structure Nehvizdyella gen. nov. from the Czech Republic and its whole‐plant reconstruction

During the Mesozoic Era, gingkoaleans comprised a diverse and widespread group. Here we describe ginkgoalean fossils in their facies context from the Late Cretaceous (Cenomanian) Peruc-Korycany Formation of the Czech Republic and present a reconstruction of tree architecture and ecology. Newly described in this study is the ovuliferous reproductive structure, Nehvizdyella bipartita gen. et sp. nov. (Ginkgoales). This ovuliferous organ consists of a bifurcating axis, terminated by large cupule-like structures, probably homologous to the collar of the recent Ginkgo. Each cupule encloses an orthotropous ovule. In specimens with the early developmental stages preserved, the entire ovule and young seed, with the exception of the micropylar area, is embedded in the cupule. Mature seeds consist of sclerotesta and sarcotesta. Monosulcate pollen grains of Cycadopites-type are found adhering to the seeds. Although similar to Ginkgo in terms of its large size and reduced number of seeds, N. bipartita differs from the extant genus in having ovules completely enclosed in a cupule-like structure. The co-occurrence of N. bipartita with ginkgoalean leaves of Eretmophyllum obtusum (Velenovský) Kvaček, J., ginkgoalean short shoots of Pecinovicladus kvacekii Falcon-Lang, and ginkgoalean trunk wood of Ginkgoxylon gruettii Pons and Vozenin-Serra in monodominant taphocoenoses at four geographically distant localities suggests that these remains all belong to one plant. This is supported by the close morphological and anatomical similarity between the different organs. Facies analysis of plant assemblages indicates that our Cretaceous tree occupied a water-stressed coastal salt marsh environment. It therefore represents the first unequivocal halophyte among the Ginkgoales.

Development of the unfertilized embryo sac and pollen tubes in the dwarf mistletoe Arceuthobium americanum (Viscaceae)

Megasporogenesis, embryo sac development, and pollen tubes in Arceuthobium americanum Nutt. ex Engelm. were investigated with light, fluorescence, and electron microscopy. The orthotropous ovular structure of A. americanum lacked integuments and possessed a nucellus that was largely continuous with and indistinguishable from the placenta; we coined this structure the placental–nucellar complex (PNC). Two megasporocytes became evident in the tenuinucellate PNC by mid-April, and had undergone bisporic megasporogenesis by mid-May. The upper cell from each dyad (distal to the base of the PNC) became a functional megaspore, although only one would develop into a seven-celled embryo sac. Like typical angiosperm embryo sacs, that of A. americanum possessed an egg cell having the ultrastructure reflective of a quiescent cell, and lacked cellulosic and (or) hemicellulosic wall material between the egg apparatus and central cell. However, the egg apparatus arose at the lower embryo sac pole, not at the upper as expected for an orthotropous ovule. A hypothetical model for the development of Arceuthobium ovules is the ancestral fusion and subsequent reduction of two anatropous ovules to form two embryo sacs within the PNC, of which only one completes development. The synergids have no role in pollen tube guidance, as tubes could be seen below each functional megaspore prior to megagametogenesis.Key words: Arceuthobium, embryo sac, megasporogenesis, mistletoe, pollen tubes, ultrastructure.

Early Cretaceous Archaefructus eoflora sp. nov. with Bisexual Flowers from Beipiao, Western Liaoning, China

Abstract Recently, whether Archaefructus has bisexual multi‐parted flowers or just inflorescences of unisexual flowers, and whether it is ancestral to all angiosperms or a derived eudicot have been debated. Here, from the same Yixian Formation, NE China, we report a new Archaefructus species, A. eoflora sp. nov., with the generic characteristics of dissected leaves and bisexual reproductive axes. It is entirely preserved with roots, rhizome, shoots and protogynous reproductive organs at different developmental stages. Its lateral and main fertile shoots form a pseudo‐indeterminate pattern, while the reproductive branches on the main shoot form a cymose inflorescence. Subtended by 1–2 bract‐like leaves, the section of stamen clusters changes into a much shorter section of carpels that have one row of orthotropous ovules. Significantly, one cluster bearing two carpels and one stamen between the two sections demonstrates a true bisexual flower, an important step of the origin of floral bisexuality, and the homology between the stamen and carpel. The complex reproductive axes represent a mix between flowers and inflorescences, and suggest that A. eoflora sp. nov. possesses the potential to evolve into a variety of diverse flower types as found in modern basal and early fossil angiosperms. A comparison with other two species also leads to a revision of the generic diagnosis.

Origin of the outer integument and its implication for the angiosperm evolution

Summery: The origin of the outer integument, which is one of the prominent synapomorphies of angiosperms, was inferred to explore the phylogenetic origin of the angiosperms. Studies based on the ovules of“ANITA”, a group of early-diverged families, revealed that the ovules with the cup-shaped outer integument are derived from the ovules with hood-shaped outer integument. The morphological marker in the seed was sought for from which the outer integument morphology could be inferred because the seeds with more fossilized potential than flowers would be helpful in deducing the primitive morphology of the outer integument based on the fossil records. As a result, I found that the relative position of the micropyle to the hilum could be used as the marker for inferring the outer integument morphology(i. e., hood-shaped or cup-shaped). Based on this marker, it is inferred that the oldest seed fossils of angiosperms are derived from the ovules with the hood-shaped outer integument. Neo- and Paleo- botanical data suggests that the hood-shaped outer integument with bilateral symmetry is primitive. The bilaterally symmetrical nature is one of the characteristics of the leaf, thus the outer integument could be homologous to the leaf. Further to examine this hypothesis I analyzed the expression pattern of INO homologue of Nymphaea alba as molecular marker for the dorsiventrality. INO homologue was limitedly expressed in the outer epidermis of the outer integument, suggesting that the outer integument has the dorsiventrality. These results imply that the outer integument is derived from the leaf.In addition to this, the carpel is suggested to be homologous to sporophyll, thus the gynoecium of angiosperms is compared to the unitegmic orthotropous ovule enclosed in two leaf-like organs, which is known in some groups of the seed ferns.