Unitegmic Ovules Research Articles

Seed and seed coat morphology in monotypic and endemic genera of Korean angiosperms

The basic information of ovule and seed characteristics was investigated for five monotypic and endemic genera in the Korean peninsula as categorized by the Flora of Korea category. The carpels and seeds were sectioned with a rotary microtome. Mature seeds were coated with platinum using an ion sputter and observed using a scanning electron microscope. As a result, <i>Abeliophyllum</i> was found to be anatropous and a unitegmic ovule, with a slightly colliculate seed surface and exotestal seed coat type. The ovule of <i>Coreanomecon</i> was anatropous and bitegmic, having a distinct echinate seed surface, and exo-endotestal seed coat type with a prismatic crystal in the mesotesta. The ovule of <i>Hanabusaya</i> was anatropous and a unitegmic, with a long reticulate seed surface sculpture, and distinct exotestal seed coat type. In addition, a wing developed at the opposite side of the raphe bundle. <i>Megaleranthis</i> was an anatropous and bitegmic ovule, having a small pentagonal disk shape, a concave seed surface and exotestal seed coat type. Finally, <i>Pentactina</i> was also anatropous and a unitegmic ovule, reticulate seed sculpture, and endotestal seed coat type. These data will be proving to be a source of good information for securing bio-sovereignty in the near future.

The anatomy of the seed-coat includes diagnostic characters in the subtribe Eugeniinae (Myrteae, Myrtaceae).

The subtribe Eugeniinae comprises of two genera, Eugenia (ca. 1,100 species) and Myrcianthes (ca. 40 species). Eugenia is the largest genus of neotropical Myrtaceae and its latest classification proposes 11 sections. This study describes the seed anatomy of forty-one species of Eugeniinae in order to provide possible diagnostic characteristics. Following standard anatomical techniques, flower buds, flowers, and fruits were processed and analyzed using microtome sections and light microscopy. The phylogeny used the regions ITS, rpl16, psbA-trnH, trnL-rpl32, and trnQ-rps16, following recent studies in the group. Ancestral character reconstruction uncovered that: (1) the ancestral ovule in Eugeniinae was campylotropous (98.9% probability), bitegmic (98.5% probability), and unitegmic ovules arose on more than one lineage independently within Eugenia; (2) the pachychalazal seed-coat appeared with a 92% probability of being the ancestral type; (3) non-lignified seed-coat (24,5% probability) and aerenchymatous mesotesta (45.8% probability) are diagnostic characters in Myrcianthes pungens (aerenchymatous mesotesta present in the developing seed-coat) and in the species of E. sect. Pseudeugenia until the species of E. sect. Schizocalomyrtus and it is the type of seed-coat that predominates in most basal sections on the tree; (4) the partial sclerification (only in the exotesta—exotestal seed-coat) is mainly observed in species of E. sect. Excelsae, E. sect. Jossinia (group X), and E. sect. Racemosae (22.2% probability); (5) and in the species of the recent lineages of Eugenia, with a probability of 27.2%, predominate the exomesotestal or testal construction of the seed-coat [character observed in almost all species analyzed of E. sect. Jossinia (group Y) and E. sect. Umbellatae]. A dehiscent fruit is considered as a plesiomorphic state in Myrtaceae; the ancestor of this family had seeds with a completely sclerified testa, and the other testa types described for the current species with dehiscent and indehiscent fruits are simplified versions of this ancestral type. Perhaps, this means that the sclerified layers in the seed-coat have remained in whole or in part as a plesiomorphic condition for taxa with a capsule and bacca. Maintaining the plesiomorphic condition may have represented a selective advantage at some point in the evolutionary history of the family and its groups.

Morphological and Structural Details of Tomato Seed Coat Formation: A Different Functional Role of the Inner and Outer Epidermises in Unitegmic Ovule

In order to understand how and what structures of the tomato ovule with a single integument form the seed coat of a mature seed, a detailed study of the main development stages of the tomato ovule integument was carried out using the methods of light and electron microscopy. The integument itself it was shown to transform in the course of development into the coat (skin) of a mature seed, but the outer and inner epidermises of the integument and some layers of the integument parenchyma are mainly involved in this process. The outer epidermis cells are highly modified in later stages; their walls are thickened and lignified, creating a unique relatively hard outer coat. The fate of the inner epidermis of integument is completely different. It is separated from the other parenchyma cells of integument and is transformed into an independent new secretory tissue, an endothelium, which fences off the forming embryo and endosperm from the death zone. Due to the secretory activity of the endothelium, the dying inner parenchyma cells of the integument are lysed. Soon after the cuticle covers the endosperm, the lysis of dead integument cells stops and their flattened remnants form dense layers, which then enter the final composition of the coat of mature tomato seed. The endothelium itself returns to the location of the integument inner epidermis.

Comparative morphology and ontogenetic patterns ofBdallophytumspecies (Cytinaceae, Malvales): insight into the biology of an endoparasitic genus

Cytinaceae are root endoparasitic plants with only three genera. Their biology is largely unknown, and most knowledge of the family is based on the Old World genus Cytinus. Here, we studied all three species of the New World Bdallophytum from Mexico. We describe their morphoanatomy, floral development, and embryology, highlighting the unique traits of Bdallophytum compared with two other genera of the family and members of Malvales. Both B. americanum and B. andrieuxii are dioecious, whereas B. oxylepis is gynomonoecious. The floral size and the number of floral organs vary within and among species, which appears to be common in Cytinaceae. The flowers of Bdallophytum exhibit synorganization in sexual organs, a synandrium in male flowers, and a gynostemium in bisexual flowers of B. oxylepis. Unisexual and bisexual flowers are zygomorphic at the early developmental stages. The unisexual flowers become actinomorphic in later development, while the bisexual flowers of B. oxylepis remain zygomorphic. The androecium of Bdallophytum has key traits shared with some Malvales, such as the fused filaments in Malvaceae and Sarcolaenaceae and the connective appendage shared with Dipterocarpaceae. Our results suggest that a unitegmic ovule is a unique trait for Bdallophytum. This is proposed here as a putative synapomorphy for Bdallophytum.

Montsechia vidalii from the Barremian of Spain, the earliest known submerged aquatic angiosperm, and its systematic relationship to Ceratophyllum

AbstractMontsechia vidalii is an abundant plant fossil from the Barremian of northeastern Spain. Systematic affinities have been suggested with several living plant clades (liverworts, horsetails, conifers, Gnetales), particularly with angiosperms. We provide detailed descriptions, documentation, and discussion of morphology and histology based on hand specimens of isolated leafy stems with fruits examined under the stereomicroscope, and with light and scanning electron microscopy. Montsechia vidalii shows shoots with flexible axes of two phyllotaxies and leaf morphologies. One morphology has opposite‐decussate leaves and stems, with small linear leaves. The other has spirally arranged leaves and stems, with inconspicuous leaves. The cuticle is thin and shows anomocytic stomata. Some stems bear terminal pairs of indehiscent fruits, probably developing from bicarpellate reproductive complexes, probably corresponding to two simple flowers each with a single carpel and arranged in indeterminate inflorescences. Every fruit contains a single seed and shows both similarities to the uniovulate ascidiate carpel that has been reconstructed as ancestral in angiosperms and derived features such as orthotropous, pendent and unitegmic ovules that are shared with the aquatic living genus Ceratophyllum. Phylogenetic analyses confirm that these similarities reflect a systematic relationship to Ceratophyllum and relatives. This and other recently described fossils, in particular Pseudoasterophyllites, suggest that this clade was diverse and ecologically significant in the Early Cretaceous. Flexible axes, thin cuticles, low number of stomata, and indehiscent fruits, as well as sedimentological and taphonomic evidence, strongly suggest a freshwater habit for M. vidalii.

Embryology of Styracaceae and implications for the evolution of the integument number in Ericales

AbstractPhylogenetic relationships in Styracaceae are well understood, but embryological characters and the ontogeny of integument(s) are still uncertain in many species. The goals of this study are to evaluate the systematic implications of embryological characters in Styracaceae, clarify the character evolution of the number of integuments and suggest a mechanism for the transition between unitegmic and bitegmic ovules. We examined the embryological characters of four genera and five species of Styracaceae, most of which were shared across taxa. However, Styrax has specific embryological features including bitegmic ovules, a multiplicative and sclerotic outer mesotesta and vascular bundles in the testa, all possible autapomorphies. The other three genera of Styracaceae share a unitegmic ovule, a parenchymatous mesotesta and a seed coat without vascular bundles, possible plesiomorphies with Diapensiaceae and Symplocaceae. The transition from a unitegmic to a bitegmic condition can be interpreted to be caused by a downwards shift of the boundary between the inner and outer integument, due to reduced activity in the subdermal initials and increased activity in the dermal initials of the outer integument at its base.

Sporogenesis and gametophytes development in Datura stramonium L. (Solanaceae)

Datura stramonium L., belonging to Solanaceae, is a medicinal plant with bioremediation potency that has variable characters and problematic taxonomy. The present study provides additional information on embryological characters in the D. stramonium that can provide useful information about the taxonomic of this species. The information is important for understanding the sexual reproduction process of this medicinal plant and also its phylogenetic position. The embryological properties, including sporogenesis and gametophyte development, of D. stramonium were examined by light, stereo, fluorescence and scanning electron microscopes. Results showed that each flower contained 5–6 tetrasporangiated stamens. The microsporogenesis and male gametogenesis characters of D. stramonium included dicotyledonous-type of anther wall formation, bi-nucleated and secretory tapetal cells, simultaneous cytokinesis in pollen mother cells, tetrahedral and tetragonal microspore tetrads and two-celled mature pollen grains. Ovary is formed by two carpels and contained numerous ovules with axile placentation. The anatropous, tenuinucellate and unitegmic ovules contained three archesporial cells. Only a single chalazal megaspore of the linear tetrad is functional. Polygonum-type embryo sac development, the presence of an endothelium, fusion of three antipodal cells and then formation of embryo without fertilization and cellular endosperm formation are the most important features in D. stramonium. The present findings reveal valuable developmental features can be used to discriminate this medicinal and environmentally important species and its phylogenetic relationships within the family Solanaceae.

Character evolution and missing (morphological) data across Asteridae.

Our current understanding of flowering plant phylogeny provides an excellent framework for exploring various aspects of character evolution through comparative analyses. However, attempts to synthesize this phylogenetic framework with extensive morphological data sets have been surprisingly rare. Here, we explore character evolution in Asteridae (asterids), a major angiosperm clade, using an extensive morphological data set and a well-resolved phylogeny. We scored 15 phenotypic characters (spanning chemistry, vegetative anatomy, and floral, fruit, and seed features) across 248 species for ancestral state reconstruction using a phylogenetic framework based on 73 plastid genes and the same 248 species. Iridoid production, unitegmic ovules, and cellular endosperm were all reconstructed as synapomorphic for Asteridae. Sympetaly, long associated with asterids, shows complex patterns of evolution, suggesting it arose several times independently within the clade. Stamens equal in number to the petals is likely a synapomorphy for Gentianidae, a major asterid subclade. Members of Lamianae, a major gentianid subclade, are potentially diagnosed by adnate stamens, unilacunar nodes, and simple perforation plates. The analyses presented here provide a greatly improved understanding of character evolution across Asteridae, highlighting multiple characters potentially synapomorphic for major clades. However, several important parts of the asterid tree are poorly known for several key phenotypic features (e.g., degree of petal fusion, integument number, nucellus type, endosperm type, iridoid production). Further morphological, anatomical, developmental, and chemical investigations of these poorly known asterids are critical for a more detailed understanding of early asterid evolution.

Sporogenesis, gametogenesis and pollen morphology of Solanum japonense and S. septemlobum (Solanaceae)

Solanum japonense Nakai and S. septemlobum Bunge are medicinal plants used chaotically in traditional Chinese medicine because they have the same Chinese name, Shuyangquan. In this study, anther wall development, microsporogenesis, male gametophyte development, megasporogenesis and female gametophyte development of S. japonense and S. septemlobum were studied using traditional paraffin section technology for the first time, and their pollen morphologies were compared using scanning electron microscopy. The results showed that both species exhibit dicotyledonous anther wall development, dual tapetum origination, secretory tapetum development, simultaneous microsporocyte cytokinesis, tetrahedral tetrad, coexistent 2-celled and 3-celled mature spheroidal pollen grains that are circular along the equatorial view and have tricolporate groves, 2 locules per ovary, axial placenta, anatropous, unitegmic and tenuinucellate ovule, linear megaspore tetrad, as well as monosporic Polygonum type of embryo sac, where the chalazal megaspore develops into the functional megaspore and the other three megaspores degenerate. However, the pollen grains of S. japonense are circular along the polar view, while those of S. septemlobum are triangular; the pollen surface ornamentation of S. japonense is granulate-verrucate-punctate, while that of S. septemlobum is granulate-punctate-fossula. These results enrich the embryological data of Solanum and provide palynological bases for the classification of these two species. https://doi.org/10.2298/ABS170724048L Received: July 24, 2017; Revised: October 20, 2017; Accepted: November 9, 2017; Published online: November 22, 2017 How to cite this article: Liu Y, Gu L, Liu J. Sporogenesis, gametogenesis and pollen morphology of Solanum japonense and S. septemlobum (Solanaceae). Arch Biol Sci. 2018;70(2):313-20.

Floral morphology and anatomy of Ophiocaryon, a paedomorphic genus of Sabiaceae.

Ophiocaryon is a lesser known genus in Sabiaceae. This study examines flowers of six Ophiocaryon species in comparison with Meliosmaalba, to identify taxonomically informative characters for understanding relationships within the family Sabiaceae, to imply previously unknown pollination mechanisms of Ophiocaryon, and to contribute to the placement of Sabiaceae within the early-diverging eudicots. Floral morphology and anatomy of six Ophiocaryon species and M. alba were studied and described using scanning electron microscopy, clearing techniques and resin sectioning. Novel characters of Ophiocaryon were identified, e.g. conical cells on petals, different kinds of orbicules in anthers, stomata on nectary appendage tips and ovary, two distinct surface patterns on stamens and ovary, tanniferous cell layers in the ovary wall, and acorn-shaped unitegmic ovules with very short integuments. Comparison of floral characters between Ophiocaryon and Meliosma found that the calyx, corolla, androecium and gynoecium of Ophiocaryon resemble an undeveloped state of the latter taxon, reflecting a paedomorphic regression of the flower of Ophiocaryon. The flower morphology and anatomy of Ophiocaryon was compared with its putative sister species M. alba, but no clear shared derived characters could be detected. Moreover, the findings of scent, presence of conical cells on petals and a nectary suggest flowers are pollinated by small insects with a secondary pollen presentation on the cupula of fertile stamens. We found that Ophiocaryon may be derived from ancestors that were similar to extant Meliosma in their flower structure and pollination mechanism. However, the lack of shared derived characters between Ophiocaryon and its phylogenetic sister group M. alba is puzzling and requires further investigations on the diversity of the latter species.

Conservation of the role of INNER NO OUTER in development of unitegmic ovules of the Solanaceae despite a divergence in protein function.

BackgroundThe INNER NO OUTER (INO) gene is expressed in the outermost cell layer of the outer integument of bitegmic ovules and is essential for this organ’s growth. The role and cross-species functional conservation of INO orthologs were examined in members of the Solanaceae, which have unitegmic ovules. Unitegmy has evolved several times in disparate angiosperm lineages. INO expression has been observed in the outermost cell layers of all examined unitegmic ovules, but the functional role of INO in unitegmic ovules has not previously been evaluated.ResultsINO orthologs were unambiguously identified in tobacco and tomato by sequence homology. Expression of the tomato INO gene was limited to the outer cell layer of the single integument indicating that this single integument has properties of the outer integument. Expression occurred only after integument initiation, later than observed in ovules of other examined angiosperms. Virus-induced knock-down of expression of the INO ortholog in tobacco inhibited growth of the outer cell layer of the integument leading to a decrease in both integument extension and curvature of the ovule. The altered ovules closely resemble those of the aberrant testa shape (ats) ino mutant combination in Arabidopsis where we see the effect of the ino mutation on a single fused integument produced by the ats mutation. Despite significant sequence identity and similar expression patterns, the tomato INO coding region was not able to complement the Arabidopsis ino mutant.ConclusionsThe similarity of effects of ino mutations on the unitegmic ovules of tobacco and the fused integuments of the Arabidopsis ats mutant show that: 1) INO orthologs play the same role in promoting integument growth in ovules of tobacco and Arabidopsis; and 2) the unitegmic ovules of tobacco (and hence other solanaceous species) are most likely the result of a congenital fusion of two ancestral integuments. Our results further indicate that INO has a conserved role in growth of the outermost cell layer of integuments. The curvature of solanaceous ovules is driven by unequal growth of the outer layers of the single integument that likely correspond to an ancestral outer integument.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0835-z) contains supplementary material, which is available to authorized users.

Transition from two to one integument in Prunus species: expression pattern of INNER NO OUTER (INO), ABERRANT TESTA SHAPE (ATS) and ETTIN (ETT).

While gymnosperm ovules have one integument, in most angiosperms two integuments surround the ovules. Unitegmic ovules have arisen independently several times during the evolution of angiosperms, but the ultimate genetic cause of the presence of a single integument remains elusive. We compared species of the genus Prunus that have different numbers of integuments: bitegmic species, such as Prunus armeniaca (apricot) and Prunus persica (peach), and unitegmic species, such as Prunus incisa, analyzing the expression pattern of genes that are involved in integument development in Arabidopsis thaliana: INNER NO OUTER (INO), ABERRANT TESTA SHAPE (ATS) and ETTIN (ETT). Bitegmic and unitegmic species showed similar INO expression patterns, indicative of the conservation of an outer integument. However, expression of ETT, which occurs in the boundary of the outer and inner integuments, was altered in unitegmic ovules, which showed lack of ETT expression. These results strongly suggest that the presence of a single integument could be attributable to the amalgamation of two integuments and support the role of ETT in the fusion of the outer and inner integuments in unitegmic ovules, a situation that could be widespread in other unitegmic species of angiosperms.

Flower morphology and anatomy of Sabia (Sabiaceae): structural basis of an advanced pollination system among basal eudicots

Flowers of four species of Sabia are investigated using scanning electron and light microscopy to understand the complex floral system of Sabiaceae and to contribute to the understanding of the systematic position of the family among early diverging eudicots. The structure of the mature flower and the floral anatomy are here described and compared with that of the sister genus Meliosma. The floral structure is relatively uniform with the greatest variability in the shape of the nectary and the differentiation of the style. Flowers share a similar pollen release mechanism, as pollen is extruded from the monosporangiate thecae through an inward-out dehiscence process leading to seemingly extrorse anthers occasionally accompanied by the curving of the upper part of the filaments. The bicarpellate ovary is divided in a synascidiate zone and a symplicate zone of similar size with two superposed unitegmic ovules per carpel. The floral Bauplan of Sabia can be interpreted as precursory to a further evolution of the monosymmetric flower of Meliosma, as both genera share numerous characters. The isolated position of Sabiaceae in the early diverging eudicots is highlighted by their unique floral morphology, although several features point to a link with Ranunculales, such as Menispermaceae. These probably reflect the existence of apomorphic tendencies shared by members of the early diverging eudicots.

Embryology of Biebersteinia (Biebersteiniaceae, Sapindales): characteristics and comparisons with related families.

Biebersteinia, a perennial herb of five species distributed from Greece to Central Asia, was long considered to be placed in, or near Geraniaceae. Recent molecular analyses, however, have shown that the genus is the sole member of the family Biebersteiniaceae in Sapindales (not including Geraniaceae). Here, we report the embryological features of Biebersteinia and provide embryological corroboration for the molecular sapindalean affinities of the genus. We compared its embryology with those of eight other families of Sapindales, as well as with those of the related orders Huerteales, Malvales, and Brassicales. Overall comparisons showed that Biebersteinia fits in Sapindales because of the presence of anther tapetal cells with polyploid nuclear mass and non-fibrous exotegmen. Further, the genus is characterized by three-celled pollen grains, tetrasporic 16-nucleate Penaea-type female gametophyte, unitegmic ovules, pseudoporogamy, and the chalaza shifting its position near the concave side in the post-fertilization stage. A considerable number of autapomorphies, combined with the lack of synapomorphies with other sapindalean families, supports placing Biebersteinia in its own family. Biebersteiniaceae appear to represent an early divergent lineage of Sapindales. Previous descriptions of seed coats, which were considered to have developed from "bitegmic" ovules, were revised.

Dynamics of early embryo development in reference to endosperm and embryo types in angiosperms

The mitotic cycle of the endosperm cells is relatively short in the firsit phases of the postfertilization development. The endosperm type does not significantly influence the duration of the mitotic cycle; it might, however, influence the dynamics of zygote and embryo development. The quick development and early end of cellular endosperm proliferation is connected with the fact that it is, in most cases, bound to small, "spare" or "saving" tenuinucellate and unitegmic ovules. Structural differences in the behaviour of the endosperm of different types, in the phase of globular and early heart embryo, might point to differences in the time or way of transition of the embryo from suspensorial to surface nutrition.

Morfología y anatomía floral de la tribu Hamelieae (Rubiaceae)

We studied floral morphology and anatomy of seven genera of the tribe Hamelieae sensu Manns & Bremer with the goal to evaluate the potential of these characters in the circumscription of the tribe. Twenty two species of Hamelieae were studied as well as ten representative species of the Cinchonoideae, Ixoroideae, and Rubioideae subfamilies for comparative purposes. The Hamelieae members had stamens adnate to the corolla base, anther dorsifixed with introrse dehiscence, amphivasal vascular bundle in the filament, endothecium of one layer of cells, papillose stigma, axile placentation, orthotropous and unitegmic ovules, epidermal cells of the integument with tannins, and idioblasts with raphides in all whorls. Exostema and Hintonia (Cinchonoideae) share with Hamelieae the stamens adnate to the corolla base and the imbricate aestivation. However, these genera are unlike of the tribe because they have anthers with latrorse dehiscence, round filaments, ovoid styles with a constriction, anatropous ovules with basipetal orientation, and idioblasts with druses or crystal sands. Rubioideae and Cinchonoideae representatives unlike Hamelieae and species of Cinchonoideae studied have valvate and contorted to the left aestivation, anthers dorsifixed at the middle, stamens adnate to the throat of the corolla, and trichomes in the throat of the corolla tube. The imbricate aestivation, the occurrence of raphides, and the adnate stamens of the corolla base supported the relationships among Hamelieae and Cinchonoideae as suggested by molecular phylogenies.

Floral Development ofStephania(Menispermaceae): Impact of Organ Reduction on Symmetry

Stephania is the sole genus in the basal eudicot family Menispermaceae that possesses both actinomorphic and zygomorphic flowers. Variation in perianth merism can have an important impact on flower symmetry and thus eminent biological significance in evolution of Menispermaceae. Using SEM, we studied the floral development of four representative species, which present the two predominant floral patterns of the genus, namely, homomorphy of both male and female flowers (actinomorphy) or heteromorphy (actinomorphy/zygomorphy). The sepals of the male flowers are arranged mostly in two alternate whorls of three or four each, whereas in female flowers they are in a single whorl of three or four or there is only a single sepal. Petals of male flowers are in a whorl of three or four organs, whereas female flowers of some species have only two petals. Trimerous and tetramerous perianths can coexist in the same umbellets of some species. Variation in perianth merism and loss of perianth parts of the female flowers may result in flower symmetry switching from actinomorphy to zygomorphy. The two main floral patterns are consistent with a distinction of two subclades within Stephania. The unicarpellate genera of the Menispermaceae share a unique combination of characters, including a synandrium, unitegmic ovules, and absence of vestigial sexual organs. However, Stephania differs from its unicarpellate relatives by two features: a two-whorled arrangement of floral organs of the male flowers and a free perianth. The investigation provides new and valuable developmental information on flowers of the little-known Menispermaceae and provides a background for a discussion of the evolution of merism and unisexual flowers in the basal eudicots.

Embryology of Withania Somnifera (L.) Dunal (Solanaceae)

We studied the embryology of Withania somnifera (L.) Dunal by light microscopy in order to reveal specific embryological features of the genus, and compared the results with embryological data on other members of the family Solanaceae. The key embryological characters of W. somnifera include dicotyledonous-type anther wall formation, simultaneous cytokinesis in pollen mother cells, binucleate tapetal cells, 2-celled mature pollen, anatropous, tenuinucellate and unitegmic ovules, polygonum-type embryo sac formation, the presence of an endothelium, and cellular endosperm formation. We give the first report of the dicotyledonous mode of anther wall formation (previously described as basic type) for the species. Comparative study suggests that anther wall formation, number of nuclei in tapetal cells, number of cells in mature pollen, mode of embryo sac formation and endosperm development are the most variable embryological features in Solanaceae. Some of these embryological features of W. somnifera should be of value for comparative study of related species and their phylogenetic relationships within the family.

Verhuellia is a segregate lineage in Piperaceae: more evidence from flower, fruit and pollen morphology, anatomy and development

The perianthless Piperales, i.e. Saururaceae and Piperaceae, have simple reduced flowers strikingly different from the other families of the order (e.g. Aristolochiaceae). Recent molecular phylogenies proved Verhuellia to be the first branch in Piperaceae, making it a promising subject to study the detailed structure and development of the flowers. Based on recently collected material, the first detailed study since 1872 was conducted with respect to morphology, anatomy and development of the inflorescence, pollen ultrastructure and fruit anatomy. Original scanning electron microscopy (SEM), transmission electron microscopy (TEM) and light microscopy (LM) observations on Verhuellia lunaria were compared with those of Piperaceae, Saururaceae and fossils. The inflorescence is an indeterminate spike with sessile flowers, each in the axil of a bract, developing in acropetal, helical succession. Flowers consist of two (occasionally three) stamens with basifixed tetrasporangiate anthers and latrorse dehiscence by a longitudinal slit. The gynoecium lacks a style but has 3-4 stigma branches and a single, basal orthotropous and unitegmic ovule. The fruit is a drupe with large multicellular epidermal protuberances. The pollen is very small, inaperturate and areolate, with hemispherical microechinate exine elements. Despite the superficial similarities with different genera of Piperaceae and Saururaceae, the segregate position of Verhuellia revealed by molecular phylogenetics is supported by morphological, developmental and anatomical data presented here. Unitegmic ovules and inaperturate pollen, which are synapomorphies for the genus Peperomia, are also present in Verhuellia.

Expression of ovule and integument‐associated genes in reduced ovules of Santalales

Santalales comprise mainly parasitic plants including mistletoes and sandalwoods. Bitegmic ovules similar to those found in most other angiosperms are seen in many members of the order, but other members exhibit evolutionary reductions to the unitegmic and ategmic conditions. In some mistletoes, extreme reduction has resulted in the absence of emergent ovules such that embryo sacs appear to remain embedded in placental tissues. Three santalalean representatives (Comandra, Santalum, and Phoradendron), displaying unitegmic, and ategmic ovules, were studied. Observed ovule morphologies were consistent with published reports, including Phoradendron serotinum, which we interpret as having reduced ategmic ovules, consistent with earlier reports on this species. For further understanding of the nature of the ovule reductions we isolated orthologs of the Arabidopsis genes AINTEGUMENTA (ANT) and BELL1 (BEL1), which are associated with ovule development in this species. We observed ovular expression of ANT and BEL1 in patterns largely resembling those seen in the integumented ovules of Arabidopsis. These genes were found to be expressed in the integument of unitegmic ovules and in the surface layers of ategmic ovules, and in some cases, expression of BEL1 was also observed in the surrounding carpel tissue. We hypothesize that ategmic ovules derive from a fusion of the integuments with the nucellus or that the nucellus has taken on some of the characteristics confined to integuments in ancestral species.