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The Acorus calamus group, or sweet flag, includes important medicinal plants and is classified into three species: A. americanus (diploid), A. verus (tetraploid), and A. calamus (sterile triploid of hybrid origin). Members of the group are famous as components of traditional Indian medicine, and early researchers suggested the origin of the sweet flag in tropical Asia. Subsequent research led to an idea of the origin of the triploid A. calamus in the Amur River basin in temperate Asia, because this was the only region where both diploids and tetraploids were known to co-occur and be capable of sexual reproduction. Contrary to this hypothesis, triploids are currently very rare in the Amur basin. Here, we provide the first evidence that all three species occur in Kazakhstan. The new records extend earlier data on the range of A. verus for c. 1800 km. Along the valley of the Irtysh River in Kazakhstan and the adjacent Omsk Oblast of Russia, A. verus is recorded in the south, A. americanus in the north, and A. calamus is common in between. We propose the Irtysh River valley as another candidate for a cradle of the triploid species A. calamus. It is possible that the range of at least one parent species (A. americanus) has contracted through competition with its triploid derivative species, for which the Irtysh River floods provide a tool for downstream range expansion. We refine our earlier data and show that the two parent species have non-overlapping ranges of variation in a quantitative metric of leaf aerenchyma structure. [ABSTRACT FROM AUTHOR]

Commonly considered bispecific, Acorus is one of the most phylogenetically isolated angiosperm genera that forms the order Acorales sister to the rest of the monocots. The Acorus calamus group is widely distributed in the Holarctic regions of Eurasia and America and has strong medicinal and other practical uses since prehistoric times. Earlier studies interpreted native diploids and invasive triploids occurring in North America as two species that differed in morphology and distribution ranges. In contrast, diploids, triploids, and tetraploids occurring in Eurasia are commonly interpreted as one species because they reportedly cannot be distinguished in collections. We resolve the controversy over taxonomic concepts between Eurasia and America and provide the first detailed multidisciplinary account of Acorus in temperate Asia. We used plastid and nuclear markers, leaf anatomy, seed micromorphology, pollen stainability, flow cytometry, and direct chromosome counts. Diploids and tetraploids show stable molecular and micromorphological differences. Triploids are their sterile hybrids, with the plastid genome inherited from the diploid parent. Diploids of America and Asia tend to differ in leaf characters. Coadaptative coexistence with pollinating beetles Platamartus jakowlewi and Sibirhelus corpulentus (Kateretidae) is conserved between diploids and tetraploids and over a distance of 4700 km between Japan and Western Siberia. Diploids are self‐compatible and can set seeds in the absence of kateretid beetles. Tetraploids are self‐incompatible and/or cannot set seeds in the absence of Platamartus and Sibirhelus. Diploids (A. americanus) and tetraploids (A. verus) are two biological species; the former has two subspecies. Acorus calamus should be restricted to triploids; it apparently first evolved in temperate Asia. Diploids mostly occur in much cooler climates than triploids and tetraploids. Accessions of A. verus and A. calamus from tropical Asia are apparently derived from ancient introductions. Our data provide a new framework for the pharmacological use of Acorus. [ABSTRACT FROM AUTHOR]

The phenomenon of heterochrony, or shifts in the relative timing of ontogenetic events, is important for understanding many aspects of plant evolution, including applied issues such as crop yield. In this paper, we review heterochronic shifts in the evolution of an important floral organ, the carpel. The carpels, being ovule-bearing organs, facilitate fertilisation, seed, and fruit formation. It is the carpel that provides the key character of flowering plants, angiospermy. In many angiosperms, a carpel has two zones: proximal ascidiate and distal plicate. When carpels are free (apocarpous gynoecium), the plicate zone has a ventral slit where carpel margins meet and fuse during ontogeny; the ascidiate zone is sac-like from inception and has no ventral slit. When carpels are united in a syncarpous gynoecium, a synascidiate zone has as many locules as carpels, whereas a symplicate zone is unilocular, at least early in ontogeny. In ontogeny, either the (syn)ascidiate or (sym)plicate zone is first to initiate. The two developmental patterns are called early and late peltation, respectively. In extreme cases, either the (sym)plicate or (syn)ascidiate zone is completely lacking. Here, we discuss the diversity of carpel structure and development in a well-defined clade of angiosperms, the monocotyledons. We conclude that the common ancestor of monocots had carpels with both zones and late peltation. This result was found irrespective of the use of the plastid or nuclear phylogeny. Early peltation generally correlates with ovules belonging to the (syn)ascidiate zone, whereas late peltation is found mostly in monocots with a fertile (sym)plicate zone. [ABSTRACT FROM AUTHOR]

The grass family (Poaceae) includes cereal crops that provide a key food source for the human population. The food industry uses the starch deposited in the cereal grain, which develops directly from the gynoecium. Morphological interpretation of the grass gynoecium remains controversial. We re-examine earlier hypotheses and studies of morphology and development in the context of more recent analyses of grass phylogenetics and developmental genetics. Taken in isolation, data on gynoecium development in bistigmatic grasses do not contradict its interpretation as a solitary ascidiate carpel. Nevertheless, in the context of other data, this interpretation is untenable. Broad comparative analysis in a modern phylogenetic context clearly demonstrates that the grass gynoecium is pseudomonomerous. A bistigmatic grass gynoecium has two sterile carpels, each producing a stigma, and a fertile carpel that lacks a stigma. To date, studies of grass developmental genetics and developmental morphology have failed to fully demonstrate the composite nature of the grass gynoecium be-cause its complex evolutionary history is hidden by extreme organ integration. It is problematic to interpret the gynoecium of grasses in terms of normal angiosperm gynoecium typology. Even the concept of a carpel becomes misleading in grasses; instead, we recommend the term pistil for descriptive purposes. [ABSTRACT FROM AUTHOR]

Ceratophyllum is an ancient and phylogenetically isolated angiosperm lineage. Comparisons between Ceratophyllum and other angiosperms are hampered by uncertainty in inferring organ homologies in this genus of specialized aquatics. Interpretation of shoot morphology is especially problematic in Ceratophyllum. Each node has several leaf-like appendages interpreted as verticillate leaves, modified parts of one and the same leaf or parts of two leaves under decussate phyllotaxis. Vegetative branches are axillary, but reproductive units (interpreted as flowers or inflorescences) are commonly viewed as developing from collateral accessory buds. We studied shoot development in Ceratophyllum submersum, C. tanaiticum, and C. demersum using scanning electron microscopy to clarify shoot morphology and branching patterns. Our data support the idea that the phyllotaxis is essentially decussate with appendages of stipular origin resembling leaf blades. We conclude that a leaf axil of Ceratophyllum possesses a complex of two serial buds, the lower one producing a vegetative branch and the upper one developing a reproductive unit. The reproductive unit is congenitally displaced to the subsequent node, a phenomenon known as concaulescence. Either member of the serial bud complex may be absent. There is a theory based on a synthesis of molecular and morphological data that Chloranthaceae are the closest extant relatives of Ceratophyllum. Serial buds and concaulescence are known in Hedyosmum (Chloranthaceae). Our new interpretation facilitates morphological comparisons between Hedyosmum and Ceratophyllum. [ABSTRACT FROM AUTHOR]

Premise: The sporoderm of seed‐plant pollen grains typically has apertures in which the outer sporopollenin‐bearing layer is relatively sparse. The apertures allow regulation of the internal volume of the pollen grain during desiccation and rehydration (harmomegathy) and also serve as sites of pollen germination. A small fraction of angiosperms undergo pollination in water or at the water surface, where desiccation is unlikely. Their pollen grains commonly lack apertures, though with some notable exceptions. We tested a hypothesis that in some angiosperm aquatics that inhabit water of unstable salinity, the pollen apertures accommodate osmotic effects that occur during pollination in such conditions. Methods: Pollen grains of the tepaloid clade of the monocot order Alismatales, which contains ecologically diverse aquatic and marshy plants, were examined using light microscopy and scanning electron microscopy. We used Ruppia as a model to test pollen grain response in water of various salinities. Pollen aperture evolution was also analyzed using molecular tree topologies. Results: Phylogenetic optimizations demonstrated an evolutionary loss and two subsequent regains of the aperturate condition in the tepaloid clade of Alismatales. Both of the taxa that have reverted to aperturate pollen (Ruppia, Ruppiaceae; Althenia, Potamogetonaceae) are adapted to changeable water salinity. Direct experiments with Ruppia showed that the pollen apertures have a role in a harmomegathic response to differences in water salinity. Conclusions: Our results showed that the inferred regain of pollen apertures represents an adaptation to changeable water salinity. We invoke a loss‐and‐regain scenario, prompting questions that are testable using developmental genetics and plant physiology. [ABSTRACT FROM AUTHOR]

Pseudomonomerous gynoecia with three (or four) carpels are unknown in the species-rich core group of Apiales, but this condition is shared by three species-poor families (Pennantiaceae, Torricelliaceae, Griseliniaceae) that form the basal grade of the order. Testing a hypothesis on the ancestral nature of carpel dimorphism in Apiales requires comparative data for all three lineages in this grade. We provide the first detailed description of flowers, including floral vasculature and gynoecium development, in a member of Pennantiaceae (Pennantia corymbosa). In contrast to many other Apiales, the inflorescence of Pennantia is paniculate and therefore has an unstable number of phyllomes in axes terminated by flowers. All phyllomes in the inflorescence are shifted onto lateral branches they subtend exhibiting recaulescence, a pattern that has not been reported elsewhere in Apiales. Plants are dioecious with functionally unisexual flowers. There are normally five stamens alternating with five petals. Anthers are present and produce pollen in stamens of male as well as female flowers, but ventral microsporangia are reduced in some anthers of female flowers. Anther morphology sometimes varies even among stamens of the same flower. Two types of synthecal anthers are recorded. Pollen dimorphism is confirmed: inaperturate pollen produced by stamens of female flowers supposedly acts as the only reward for pollinators in the absence of nectaries. The gynoecium of the female flower is syncarpous and pseudomonomerous: only one of three carpels is fertile. The gynoecium is initiated as three carpel primordia (future stigmas). One of them is smaller than the other two and occupies an alternistaminal (and antepetalous) position. The two large carpel primordia are located in the radii of stamens that are generally smaller (early in development) than the three other stamens. The carpel dimorphism is maintained at anthesis. The carpel with the smaller stigma is fertile, and those with larger stigmas are sterile. The carpels are congenitally united below the stigmas. The ovary is superior, unilocular (vs. inferior and plurilocular in Torricelliaceae and Griseliniaceae) and usually uniovulate with pendent ovule(s) inserted at the cross-zone level of the fertile carpel. As in most other Apiales, the short symplicate zone is sealed by postgenital fusion at anthesis and forms an internal compitum. The fertile carpel of the members of the basal grade of Apiales investigated so far is uniformly arranged in a petal radius. This is consistent with the idea that pseudomonomery is associated with stable patterns of flower groundplan in Apiales. Our data do not provide any clear structural or developmental evidence of independent origins of carpel dimorphism in Pennantiaceae, Torricelliaceae and Griseliniaceae. [ABSTRACT FROM AUTHOR]

Anarthria, Lyginia and Hopkinsia, endemic to south-western Western Australia, differ from the rest of Restionaceae sensu APG IV in the presence of dithecal rather than monothecal anthers. Dithecal and monothecal Restionaceae form two well-supported sister clades in molecular phylogenetic trees, but shared morphological features of Anarthria, Lyginia and Hopkinsia known so far are either symplesiomorphies (e.g. anther structure) or are characters that are homoplastic in monocots (e.g. absence of silica in culms). The taxonomic placement of the three genera has been controversial during the 20th century, including the idea of recognizing three monogeneric families. As comparative morphological data covering all three genera are limited, we provide a study of female flower structure and development in this group. This is the first developmental study of dithecal Restionaceae that uses scanning electron microscopy. With many more investigated characters, like earlier studies, we found no potential synapomorphies for the dithecal clade. However, we found the first morphological support for the conclusion from molecular data of a sister relationship between Hopkinsia and Lyginia. They share ovules with length not exceeding the width and the micropyle oriented towards the dorsal side of the carpel, which is probably a synapomorphy. Some other characters shared by the two genera could be plesiomorphic, such as inner whorl tepals that are shorter than the gynoecium throughout development. Contrary to some earlier reports, female flowers of all three genera are arranged in spikelets and do not have bracteoles. These characters are thus conserved across the restiid and graminid clades. The gynoecium of Hopkinsia is unicarpellate and not pseudomonomerous. Gynoecia with a single fertile ovule appeared several times and through different morphological pathways in the evolution of wind-pollinated Poales. [ABSTRACT FROM AUTHOR]

Transitions in corolla symmetry are an important aspect of angiosperm floral evolution. Contort petal aestivation is common in several groups of eudicots. In rosids, the direction of overlap between adjacent petals (handedness) of the contort corolla is often labile among flowers in a single inflorescence, but in asterids, handedness is usually stable at a supraspecific level. Taxa with contort corolla are unevenly distributed among asterids, and detailed developmental data are often lacking. We provide the first developmental study of flowers in Melanophylla (Torricelliaceae, Apiales), the only known campanulid with a contort corolla, and demonstrate that the corolla handedness is labile within a single inflorescence. Labile handedness distinguishes Melanophylla from members of lamiids with a contort corolla where handedness is stable. In Melanophylla, the handedness is determined by the arrangement of bracteoles. Petals are asymmetric from early developmental stages. The androecium is also usually contort, with handedness always opposite to that of the corolla. Anthers have broad, flat connectives, which is unusual in asterids. The gynoecium is pseudomonomerous, with the fertile carpel in a left or right-transversal position, depending on the handedness of the corolla and androecium. Symmetry patterns of all floral whorls, including the pseudomonomerous gynoecium, are strongly correlated in Melanophylla, in contrast with the unstable carpel orientation in monomerous gynoecia of Apiales studied so far. The tricarpellate pseudomonomerous gynoecia of Melanophylla and other early divergent Apiales resemble those of Dipsacales. [ABSTRACT FROM AUTHOR]

Collateral bundles with external position of the phloem characterize the stem vasculature of most seed plants. An earlier study highlighted the occurrence of inverted peripheral bundles in the leafless inflorescence peduncle of the rare Australian aquatic Maundia triglochinoides. This unusual feature and other morphological and molecular data supported the recognition of the monogeneric Maundiaceae, but the anatomy of the leaves, rhizomes and roots of Maundia remained unknown and is studied here. Maundia has an iterative sympodial growth with all shoots bearing five tubular cataphylls splitting longitudinally and simulating open sheaths at maturity and two (or three) linear foliage leaves without a conspicuous basal sheath. This morphology distinguishes Maundiaceae from all other Alismatales. The rhizome has an atactostele with collateral bundles of normal orientation; peripheral bundles are absent. Cataphylls have a series of normally oriented bundles. Foliage leaves are thick, bifacial, semi-elliptical in cross-section, with a thin subepidermal layer of chlorenchyma on both sides, accompanied by peripheral bundles with xylem facing outwards (thus abaxial peripheral bundles are inverted) and central large bundles of normal orientation. Strong anatomical similarity between leaves and peduncles is related to their shared function as assimilatory organs. As in angiosperm succulents, the three-dimensional leaf venation in thick aquatic and helophyte leaves of Alismatales serves to reduce transport distances between veins and photosynthetic cells. In both cases, the patterns of orientation of peripheral bundles (with inverted adaxial or abaxial bundles) are unstable in large clades. These slender bundles cannot be used for the identification of unifacial leaves. Some anatomical characters express homoplastic similarities between Maundiaceae and Aponogetonaceae. [ABSTRACT FROM AUTHOR]

Scheuchzeria palustris, the only member of Scheuchzeriaceae, is unique among Alismatales in several characters, including flower-subtending bracts with conspicuous laminas and pollen dispersed in permanent dyads. Earlier studies revealed unidirectional flower development in some monocots with massive flower-subtending bracts, but not in Scheuchzeria. Permanent pollen or spore dyads are extremely rare among extant land plants and in no case have they been studied developmentally. The paper provides new data on flower development and the first description of pollen development in Scheuchzeria. Flowers are arranged in a closed raceme. Development of lateral flowers is unidirectional, with delayed initiation of abaxial tepals and stamens. Flowers are often trimerous and pentacyclic, but numerous deviations from this groundplan are observed. Dyad development is investigated from microspore mother cells to mature pollen and their germination by electron microscopy and cytochemical methods. Meiosis is successive. Tetrads are irregular (42%), tetragonal (35%), decussate (13%), linear (7%) and T-shaped (3%). During the tetrad period, the microspores are surrounded by a callose special wall of different thickness. Disintegration of tetrads into two dyads takes place along the plane of the first cytokinesis, where the thickness of the callose wall is maximal. Pollen grains are held together in the dyads due to a simple fusion of tectal layers, this fusion takes place at the late tetrad period. Developmental data did not reveal any possible aperture sites in Scheuchzeria. This favours the hypothesis of complete loss and subsequent regain of apertures in the course of evolution of the 'tepaloid clade' of Alismatales. [ABSTRACT FROM AUTHOR]

PREMISE OF THE STUDY: The small primarily Australian commelinid monocot family Centrolepidaceae displays remarkably high structural diversity that has been hitherto relatively poorly explored. Data on Centrolepidaceae are important for comparison with other Poales, including grasses and sedges. METHODS: We examined vegetative and reproductive morphology in a global survey of Centrolepidaceae based on light and scanning electron microscopy of 18 species, representing all three genera. We used these data to perform a cladistic analysis to assess character evolution. KEY RESULTS: Each of the three genera is monophyletic; Centrolepis is sister to Aphelia. Some Centrolepidaceae show a change from spiral to distichous phyllotaxy on inflorescence transition. In Aphelia and most species of Centrolepis, several morphologically distinct leaf types develop along the primary shoot axis and flowers are confined to dorsiventral lateral spikelets. Centrolepis racemosa displays secondary unification of programs of leaf development, absence of the leaf hyperphyll and loss of shoot dimorphism. Presence or absence of a leaf ligule and features of inflorescence and flower morphology are useful as phylogenetic characters in Centrolepidaceae. CONCLUSIONS: Ontogenetic changes in phyllotaxy differ fundamentally between some Centrolepidaceae and many grasses. Inferred evolutionary transformations of phyllotaxy in Centrolepidaceae inflorescences also differ from those in grasses. In contrast with grasses, some Centrolepidaceae possess ligulate leaves where the ligule represents the boundary between the bifacial hypophyll and unifacial hyperphyll. All the highly unusual features of the morphological-misfit species Centrolepis racemosa could result from the same saltational event. Centrolepidaceae offer good perspectives for studies of evolutionary developmental biology. [ABSTRACT FROM AUTHOR]

The monogeneric early-divergent angiosperm family Hydatellaceae ( Trithuria) was formerly placed in the monocots and shows several features that are at least superficially monocot-like. Seedlings of Hydatellaceae are unusually diverse and have been interpreted as either dicotylar or monocotylar. We provide the first detailed developmental description of seedlings of Trithuria lanterna (including the first data on mature embryos of tropical Hydatellaceae) as a basis for the general discussion of seedling diversity in Hydatellaceae. Seedlings at various stages after germination were studied using serial sections and scanning electron microscopy. The embryo is dicotylar. It lacks pronounced asymmetry and lacks a plumule before seed germination. In the majority of seedlings, the cotyledons are free and appear attached to the seedling axis at different levels. In other seedlings, the cotyledons are united via a non-haustorial leaf-like organ; this alternative condition represents a novel type of syncotyly for seed plants and a second type of syncotyly recorded for Hydatellaceae. Seedling morphology is determined by strong one-sided growth of the hypocotyl, which is an unusual way of overcoming the basic seed plant spatial constraint at germination. The direction of one-sided growth is independent of cotyledon orientation and could be environmentally determined. Seedlings provide synapomorphies for the two major clades of Trithuria, which can be regarded as subgenera. Although no direct homology is inferred, the exceptional degree of morphological variation in Hydatellaceae seedlings, including the variable occurrence of several superficially monocot-like features, leads us to hypothesize that the stem group of monocots could have exhibited an analogous degree of variation in cotyledon morphology. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 174, 551-573. [ABSTRACT FROM AUTHOR]

We provide the first detailed description of specialized anatomical mechanisms of fruit dehiscence in two sections of Trithuria (Hydatellaceae), a basal angiosperm lineage with a markedly ascidiate carpel. The dehiscent fruits of Hydatell-aceae are unique among angiosperms. Earlier studies suggested the follicle as a primitive type of dehiscent angiosperm fruit, developing from a conduplicate carpel. In contrast with follicles, the single-seeded apocarpous (or unicarpellate) dehiscent fruits of Hydatellaceae dehisce by three equally spaced valves separating from three fruit ribs. There is no evidence of pseudo-monomery. In mature fruits, all cell layers except the outer epidermis of the ovary are obliterated, so that only one pericarp layer (the exocarp) remains, except in the regions around the vascular bundles and at the fruit apex and base. Morphological cladistic analyses reveal data incongruence between characters describing fruit morphology and other morphological features of Hydatellaceae, including those linked with dioecy/monoecy. As a result, strict consensus trees inferred from maximum parsimony analyses based on each of the two sub-sets of morphological data are more resolved than ones inferred from the analysis of the entire morphological dataset. Fruit characters correspond closely with the recently published molecular phy-logeny of the sole genus, Trithuria. The occurrence of an apparently rudimentary mechanical tissue at the fruit apex of most Hydatellaceae with indehiscent fruits suggests that the stem group of Hydatellaceae was characterized by dehiscent fruits with lignified endocarp fibres. The occurrence of Strelitzia-type surface waxes characteristic of Trithuria sect. Trithuria provides further evidence of the homoplasy of this epicuticular wax type at the scale of seed plants. [ABSTRACT FROM AUTHOR]

Floral symmetry is widely known as one of the most important structural traits of reproductive organs in angiosperms. It is tightly related to the shape and arrangement of floral parts, and at the same time, it plays a key role in general appearance (visual gestalt) of a flower, which is especially important for the interactions of zoophilous flowers with their pollinators. The traditional classification of floral symmetry divides nearly all the diversity of angiosperm flowers into actinomorphic and zygomorphic ones. Within this system, which is useful for ecological studies, many variations of symmetry appear to be disregarded. At the same time, the diversity of floral symmetry is underpinned not only by ecological factors, but also by morphogenetic mechanisms and constraints. Sometimes it is not an easy task to uncover the adaptive or developmental significance of a change of the floral symmetry in a particular lineage. Using the asterid order Apiales as a model group, we demonstrate that such changes can correlate with the merism of the entire flower or of its particular whorl, with the relative orientation of gynoecium to the rest of the flower, with the presence of sterile floral elements and other morphological characters. Besides, in some taxa, the shape and symmetry of the flower change in the course of its development, which should be taken in consideration in morphological comparisons and evaluations of synapomorphies in a particular clade. Finally, we show that different results can be obtained due to employment of different approaches: for instance, many flowers that are traditionally described as actinomorphic turn out to be disymmetric, monosymmetric, or asymmetric from a more detailed look. The traditional method of division into actinomorphy and zygomorphy deals with the general appearance of a flower, and mainly considers the shape of the corolla, while the geometrical approach handles the entire three-dimensional structure of the flower, and provides an exact number of its symmetry planes. [ABSTRACT FROM AUTHOR]