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Premise of research. In Caryophyllaceae with a gynoecium isomerous with the other floral whorls, carpels can be in either antesepalous or antepetalous position. Morphologists have long been unable ...

This review based on a morphological and developmental perspective reveals a striking diversity in shapes and evolutionary trends in the gynoecium of core Caryophyllales that have affected the number of carpels, the formation of septa and the number of ovules. Two major developmental shifts are responsible for the diversity in gynoecial forms and are linked to the proportional development of carpellary tissue (ovary wall) and the floral apex. (1) Meristic change is caused by an expansion or reduction of the diameter of the floral apex. An expansion leads to polygyny linked with the development of more numerous small carpels; a reduction of space leads to lower carpel numbers, eventually resulting in a single carpel. (2) Different ovary shapes can be recognized at a mid-developmental stage predicting the further development of ovaries. With an equal growth of the ovary wall and floral apex, young ovaries take the shape of a salt-shaker; with more extensive development of the floral apex and delay of the ovary wall, a club-shaped ovary is formed; with faster growth of the ovary wall linked with intercalary expansion and a delayed growth of the floral apex, a (half-) inferior cup-shaped ovary develops. The different growth forms are the results of heterochronic shifts and affect the development of septa and ovule numbers. A common trend in the order implies a weakening and break-up of septa during development, leading to residual apical and basal septa and the shift to free-central and basal placentation. The club-shaped ovary is linked with an almost complete loss of septa and a reduction of the ovule number to one. The salt-shaker shape leads to ovaries with a massive placental column and several ovules. The cup-shaped ovary leads to a shift of ovules away from the floral apex. Developmental flexibility is responsible for a disconnection of carpel wall growth from ovular tissue. Subtle shifts in proportional growth lead to a high diversification of ovaries in core Caryophyllales and the establishment of predictable developmental trends. These trends clearly represent apomorphic tendencies, affecting different families of core Caryophyllales in different degrees. The ancestral gynoecium was probably pentamerous and isomerous with the other floral whorls, with ovules clearly separated from the carpellary wall and inserted on axile placentas corresponding to the central axis of the flower.

Between 2001 and 2017, the Royal Botanic Garden Edinburgh conducted training and research in Belize built around an annual two-week field course, part of the Edinburgh M.Sc. programme in Biodiversity and Taxonomy of Plants, focused on tropical plant identification, botanical-collecting and tropical fieldwork skills. This long-term collaboration in one country has led to additional benefits, most notably capacity building, acquisition of new country records, completion of M.Sc. thesis projects and publication of the findings in journal articles, and continued cooperation. Detailed summaries are provided for the specimens collected by students during the field course or return visits to Belize for M.Sc. thesis projects. Additionally, 15 species not recorded in the national checklist for Belize are reported. The information in this paper highlights the benefits of collaborations between institutions and countries for periods greater than the typical funding cycles of three to five years.

Most Rosaceae flowers are pentamerous and have petals, but subtribe Sanguisorbinae have small tetramerous (or trimerous) flowers without petals, and their floral morphology and morphogenesis remain poorly known. We investigated the floral development of three Sanguisorba spp. using scanning electron microscopy to clarify the relationship between floral development and mature flowers, with emphasis on floral constraints affecting reduction of petals, diversity of androecial patterns and the development of the gynoecium and ovule, and to clarify the pollination mechanisms in the absence of petals. All species have botryoids, with numerous flowers initiated acropetally, and the maturation of flowers follows different directions. All flowers are tetramerous and sepals emerge pairwise. No petal primordia appear. Antesepalous stamens are initiated in a pairwise manner; only S. hakusanensis has a second whorl. The ovary appears inferior by development of a cystiform hypanthium. There is only one ovule with a single integument by reduction of the inner. The space occupied by the larger sepals forces the stamens to develop sequentially. Our data demonstrate that petals are basically absent and that there is a possible shift of pollination mechanisms in Sanguisorba among the mainly wind-pollinated Sanguisorbinae, as both anemophilous and entomophilous characters are found in this genus.

Mechanical forces acting within the plant body that can mold flower shape throughout development received little attention. The palette of action of these forces ranges from mechanical pressures on organ primordia at the microscopic level up to the twisting of a peduncle that promotes resupination of a flower at the macroscopic level. Here, we argue that without these forces acting during the ontogenetic process, the actual flower phenotype would not be achieved as it is. In this review, we concentrate on mechanical forces that occur at the microscopic level and determine the fate of the flower shape by the physical constraints on meristems at an early stage of development. We thus highlight the generative role of mechanical forces over the floral phenotype and underline our general view of flower development as the sum of interactions of known physiological and genetic processes, together with physical aspects and mechanical events that are entangled towards the shaping of the mature flower.

We investigated the floral anatomy and development of Macarthuria australis Hügel ex Endl., an unusual genus endemic to Australia, in the context of floral evolution of core Caryophyllales. Flower initiation is spiral, with sepals developing quincuncially. The first two petals continue the sequence of sepal initiation, but the remaining petals arise from common stamen–petal primordia. The androecium develops sequentially as three inner antesepalous and five outer antepetalous stamens. The globular ovary is trimerous with a short symplicate zone and two arillate ovules per locule. The rapid emergence of the androecium leads to a partial absorption of the petal primordia within the androecial tissue. The two first-formed petals have more room for development and precede the androecium, supporting the fact that petals are not staminodial in origin. This heterochronic shift correlates with an inversed developmental sequence of the antesepalous stamens. The constraint caused by the spatial occupation of sepals and carpels leads to the loss of two stamens, and the re-arrangement of stamens and petals along the flanks of the carpels. The floral development of Macarthuria anticipates a syndrome of stamen and petal development in other core Caryophyllales and culminating in the Caryophyllaceae.

The flower of Malesherbia Ruiz & Pav. (Passifloraceae) is a suitable model to study how far growth constraints throughout ontogeny are causal for the variation in the proportions of reproductive structures. The Malesherbia flower is characterized by a marked hypanthium subtending five alternating sepal and petal lobes plus a coronal rim. In Malesherbia, the size relation between hypanthial tube and perianth lobes conditions the general aspect that the flower of a given species may display. For instance, flowers of taxa belonging to the section Malesherbia are characterized by a predominant hypanthium much similar to tubular flowers with reduced erect perianth lobes and a protruding paracorollar cylinder, while the opposite is true for the remaining species of the genus resembling a radiate ten-parted open flower with a reduced corona. Further morphological variation in the genus includes the bimodal distribution of absolute size of the mature flower, with some species showing much smaller dimensions (e.g., M. humilis) and also the variability in the level of aggregation of the inflorescences ranging from uniflorous (M. lactea), through racemose (M. densiflora, M. lirana) up to very condensed and globular in shape (M. fasciculata). In this work we studied under SEM the flower morphogenesis of 14 Malesherbia species collected in the Andean and desertic region of septentrional Chile. Against expectations, our data showed that the growth of petal lobe primordia is relatively faster in tubular flowers than in radiate ones, despite the presence of a much showier perianth at maturity in the latter. Absolute flower size could also be related to absolute meristem size and a relative developmental arrest was detected in the flower buds of very condensed inflorescences. Our results support the idea of a common constraint throughout ontogeny in which earlier inception and faster organ growth leads to relatively smaller dimensions coupled with earlier maturation and arrest of elongation.

We observed the floral development of Hemiorchis burmanica and two species of Gagnepainia, which make up the sister group of Globba in Globbeae, as well as a selected number of species of Globba. Our observations revealed that in Gagnepainia a “fifth staminode” develops as part of the labellum, while it is generally lost in other Zingiberaceae. The fifth staminode, however, was not initiated in the labellum of Hemiorchis. A fifth staminode was also observed in Globba geoffrayi, but was not found in all other species of Globba investigated. While the staminode becomes integral part of the labellum in Gagnepainia, it remains small and almost aborts at later stages of development in Globba geoffrayi. These results indicate that the development of a fifth staminode could be a recurring plesiomorphic trait for Globbeae, only retained in G. geoffrayi. The retention of the fifth staminode and its heterochronic shift may be linked with the mechanical constriction within the flower bud. The results may also support the interpretation of an atavistic expression of a once lost staminode.

Croton is a mega-diverse genus of more than 1,200 species with great morphological diversity and highly dimorphic flowers. Staminate flowers generally possess petals and a variable number of stamens and lack of an ovary. Pistillate flowers generally lack petals or have filamentous structures instead; stamens are lacking, and the ovary is generally tricarpellate with divided styles. However, well-developed petals can be found in pistillate flowers of some African species and two New World sections, i.e., sect. Alabamenses and sect. Eluteria subsect. Eluteria. Our objectives are to compare ontogeny in dimorphic flowers of Croton which may elucidate the origin of petals, homology of the filamentous structures, nectaries, and diversity of the androecium. The development of staminate and pistillate flowers of C. alabamensis (sect. Alabamenses) and C. schiedeanus (sect. Eluteria) was studied under the scanning electron microscope (SEM) and compared with C. chilensis (sect. Adenophylli) which has filamentous structures in pistillate flowers. In staminate flowers, petals develop in alternation with sepals and later the outermost stamen whorl develops opposite to the petals. In a much later stage, nectar glands emerge in alternation with the petals. In pistillate flowers, filamentous structures and petals share the same early development in alternation with the sepals. However, growth of the filamentous structures of C. chilensis becomes arrested, while petals of C. alabamensis and C. schiedeanus develop similar to those of the staminate flowers. The main conclusions of the study are: (1) Petals and filamentous structures are homologous based on their location and shape in early development. (2) Nectaries with variable morphology develop in antesepalous position and probably represent receptacular outgrowths and are not staminodial. (3) Staminate flower development displays an unexpected diversity, including a floral cup in C. alabamensis. All investigated species have an unusual centrifugal initiation of the second stamen whorl. (4) The possible evolutionary loss and potential regain of petals among different species of Croton is discussed in relation to heterochrony. We suggest that the filamentous structures in pistillate flowers represent pedomorphic forms of petals of staminate flowers, and that the well-developed petals in C. alabamensis and C. schiedeanus are derived via a developmental reversion., PT was funded by the Development and Promotion of Science and Technology talents project (DPST) Scholarship, Royal Thai Government. SR was supported by the Scottish International Education Trust. The Royal Botanic Garden Edinburgh was supported by the Scottish Government’s Rural and Environment Science and Analytical Services Division.

Globba is one of the largest genera in the primarily tropical Zingiberaceae. The number of anther appendages is highly diagnostic and has been used along with molecular characters to define subgenera and sections. Four main types of anther morphology are recognized: without appendages and with two, four and six appendages. The six-appendaged anthers are reported here for the first time. Appendages arise from two dorsal ledges that flank the broad connective. Development of two-appendaged and four-appendaged species differs from inception. Previous suggestions that either the proximal or distal appendages of four-appendaged anthers have been lost in two-appendaged species are thus not supported. Early development of six-appendaged anthers is similar to that of four-appendaged species, but two additional, small appendages develop on the ledges between the first-formed appendages. This yields three appendages on each side (six overall). The four appendages of G. geoffrayi differ from all other species in having distal appendages that are much smaller and develop later than the proximal appendages. Development thus suggests that the state in G. geoffrayi evolved from a two-appendaged ancestor. Incorporating this information into a phylogenetic character plot of the number of appendages shows that the possession of two appendages is the most likely plesiomorphic state of the genus, although support for this hypothesis is weak. Our study clarifies the origin and complexity in the development of anther appendages in Globba and highlights their significance in infrageneric relationships in Globba. Two appendages have probably likely arisen at the base of Globba, linked with the presence of a prominent ledge, with variable extensions and reductions of the number of appendages in the various subgenera and sections.

The floral organogenesis and anatomy of Koelreuteria bipinnata and its variety K. bipinnata var. integrifolia (Sapindaceae) has been investigated to clarify the identity of the two taxa in relation to other species of Koelreuteria, and to understand the shift to monosymmetry in the genus. Although the floral development is highly similar, we found a number of striking differences. Flowers arise in thyrses, with lateral branches forming cincinni of 5–9 flowers. Sepals initiate in a spiral sequence. Five petals arise unidirectionally alternating to the sepals. The last formed petal and one stamen between sepals 3 and 5 are strongly delayed, appearing as a common primordium, while this petal is completely suppressed in var. integrifoliola. Eight stamens initiate sequentially, differ in size and partly precede the development of petals. The gynoecium develops as a triangular primordium on which three carpellary lobes become demarcated simultaneously. Placentation is axile. Septal slits occurring within the style are interpreted as a deep-reaching non-nectariferous extension of the stigma. The massive, oblique disk with crenate apex develops in an extrastaminal position, but is interrupted on the radius of the lost petal. Floral developmental evidence supports variety K. bipinnata var. integrifolia rather than being synonym of K. bipinnata. Floral development is compared with K. paniculata and is discussed in the context of floral evolution of Sapindaceae. Our study demonstrates the importance of developmental shifts on floral evolution. The triangular gynoecium has a strong spatial impact in obliquely reorganizing the symmetry of the flower. It is demonstrated that spatial constraints of calyx and ovary are responsible for the reduction in one of the petals, two stamens and a shift in symmetry of the flower.

Premise of research. The floral development of the monotypic genus Medusagyne is investigated to understand the mechanisms of stamen and carpel increases in light of its proposed affinity with Ochnaceae.Methodology. Flowers at different stages of development were investigated with SEM.Pivotal results. Flowering shrubs are andromonoecious. Flowers arise in cymes at the end of shoots. Initiation of staminate and bisexual flowers is similar for sepals and petals, which arise in a spiral sequence. Stamen initiation is centrifugal on a broad circular primordium but becomes more or less irregular by the insertion of additional stamens between the older stamens. In staminate flowers the globular floral apex is completely covered with stamens, with no trace of carpels. Bisexual flowers emerge on the lower branches and develop a broad stamen ring surrounding a whorl of 13–16 carpels. Carpels initiate in a ring around the massive floral apex and develop mainly in a vertical direction. Carpels are progressively swam...

The digitization of herbaria and their online access will greatly facilitate access to plant collections around the world. This will improve the efficiency of taxonomy and help reduce inequalities between scientists. The Botanic Garden Meise, Belgium, is currently digitizing 1.2 million specimens including label data. In this paper we describe the user requirements analysis conducted for a new herbarium web portal. The aim was to identify the required functionality, but also to assist in the prioritization of software development and data acquisition. The Garden conducted the analysis in cooperation with Clockwork, the digital engagement agency of Ordina. Using a series of interactive interviews, potential users were consulted from universities, research institutions, science-policy initiatives and the Botanic Garden Meise. Although digital herbarium data have many potential stakeholders, we focused on the needs of taxonomists, ecologists and historians, who are currently the primary users of the Meise herbarium data portal. The three categories of user have similar needs, all wanted as much specimen data as possible, and for those data, to be interlinked with other digital resources within and outside the Garden. Many users wanted an interactive system that they could comment on, or correct online, particularly if such corrections and annotations could be used to rank the reliability of data. Many requirements depend on the quality of the digitized data associated with each specimen. The essential data fields are the taxonomic name; geographic location; country; collection date; collector name and collection number. Also all researchers valued linkage between biodiversity literature and specimens. Nevertheless, to verify digitized data the researchers still want access to high quality images, even if fully transcribed label information is provided. The only major point of disagreement is the level of access users should have and what they should be allowed to do with the data and images. Not all of the user requirements are feasible given the current technical and regulatory landscape, however, the potential of these suggestions is discussed. Currently, there is no off-the-shelf solution to satisfy all these user requirements, but the intention of this paper is to guide other herbaria who are prioritising their investment in digitization and online web functionality., SCOPUS: ar.j, info:eu-repo/semantics/published

Heterostylous species present at least two flower morphs: one is ‘long-styled’ with a gynoecium overtopping the anthers, and another ‘short-styled', presenting the stigma below the anther level. This study investigates how both morphotypes arise through ontogeny using Oxalis cinerea Zucc. and Oxalis rosea Jacq. as study models. We found that long-styled flowers originate from comparatively larger floral meristems that allocate a broader meristematic area to gynoecium inception. Hence long-styled young flowers possess an overall larger size than short-styled ones with a broader and slow-maturing gynoecium. When the flower bud is about 1 mm in diameter, the stylodia overtop the long anthers attaining the typical long-styled configuration. Flower meristematic size appears to be a key determining aspect in the evolution of floral heterostylous morphotypes, playing a role in growth behaviour of the gynoecium.

This study illustrates the intricate floral development of Lewisia (Montiaceae) in an evolutionary context. Flowers are enclosed by two median bracteoles (involucrum), as most Portulacinae. Unlike most taxa of the Montiaceae (Caryophyllales), the petaloid perianth in Lewisia develops in two clearly separate steps: two lateral petaloids arise immediately after bracteole initiation, while the median petaloids lag behind and develop only after the stamens. Stamen number fluctuates between five and more than fifty. In studied species, the number of median petaloids is generally increased from three up to 17 organs, in close connection with the androecium. The involucrum has a strong influence on the arrangement of organs in the flower, by: (1) causing a delay on the growth and development of the petaloids, and (2) by moulding the floral apex in an elliptical shape, allowing an increase of median petaloid and stamen numbers, independently of changes in carpel number. Carpel number influences the position and number of upper stamens. Mechanical pressure of the enclosing involucrum plays a crucial role in the evolution of species of Lewisia and those species with fewer petaloids and stamens correspond to the ancestral condition.

The first molecular phylogenies of the flowering plant family Ranunculaceae were published more than twenty years ago, and have led to major changes in the infrafamilial classification. However, the current phylogeny is not yet well supported, and relationships among subfamilies and tribes of Ranunculaceae remain an open question. Eight molecular markers from the three genomes (nuclear, chloroplast and mitochondrial) were selected to investigate these relationships, including new markers for the family (two homologs of the nuclear CYCLOIDEA gene, the chloroplast gene ndhF, and the mitochondrial intron nad4-I1). The combination of multiple markers led to better resolution and higher support of phylogenetic relationships among subfamilies of Ranunculaceae, and among tribes within subfamily Ranunculoideae. Our results challenge the monophyly of Ranunculoideae as currently circumscribed due to the position of tribe Adonideae (Ranunculoideae), sister to Thalictroideae. We suggest that Thalictroideae could be merged with Ranunculoideae in an enlarged single subfamily.

Sapotaceae belongs to the heterogeneous order Ericales and exhibits extensive diversity in floral morphology. Although pentamery is widespread and probably the ancestral condition, some clades are extremely variable in merism, with fluctuations between tetramery to hexamery and octomery, affecting different floral organs to different degrees. We assessed the different states of merism in Sapotaceae to determine the evolution of this character among different clades. The floral morphology and development of nine species from eight genera were investigated using scanning electron microscopy (SEM). Furthermore, floral characters related to merism were mapped onto a phylogenetic tree to analyse the distribution and evolutionary significance of merism in the family. Developmental evidence shows that changes in merism are linked to a concerted multiplication of organs among whorls and an increase in whorls through the displacement of organs. Although pentamery is reconstructed as the ancestral condition, a reduction to tetramery or an increase to a higher merism (mainly hexamery or octomery) has evolved at least five times in the family. Fluctuations in merism between different whorls are not random but occur in a coordinated pattern, presenting strong synapomorphies for selected clades. Octomery has evolved at least twice, in Isonandreae from tetramery and in Sapoteae-Mimusopinae from pentamery. Hexamery has evolved at least three times, independently in Northia, the Palaquium clade of Isonandreae and derived from octomery in Sapoteae-Mimusopinae. Three possibilities of merism increase have been identified in Sapotaceae: (1) a concerted increase affecting all organs more or less equally (Palaquium clade of Isonandreae, Sapoteae); (2) a coordinated increase in petals, stamens and mostly carpels without effect on sepals (Labourdonnaisia, Payena–Madhuca clade of Isonandreae); (3) an increase in carpels independently of other organs (Burckella, Letestua, Labramia, etc.). A major shift affecting all Sapotaceae, except Isonandreae, is the sterilization or loss of the antesepalous stamen whorl. The presence of two fertile stamen whorls in Isonandreae indicates a possible reversal or a retained plesiomorphy. In a number of genera, stamens are secondarily increased independently of changes in merism. Descriptions of flowers listing only organ numbers are thus misleading in the inference of evolutionary relationships, as they do not differentiate between changes in merism affecting the number of perianth whorls and other changes affecting the androecium, such as sterilization, loss or occasional doubling of antepetalous stamens. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, ●●, ●●–●●.

PREMISE OF THE STUDY The phylogenetic position of Ceratophyllum is still controversial in recent molecular analyses of angiosperms, with various suggestions of a sister group relation to all other angiosperms, eudicots, monocots, eudicots + monocots, and magnoliids. Therefore, the morphological characters of Ceratophyllum are important for resolving the phylogeny of angiosperms. In this study, we observed the detailed developmental anatomy of all lateral organs and their configurations to elucidate the floral development and phyllotactic pattern of Ceratophyllum demersum. METHODS We observed fixed shoots of C. demersum with scanning electron microscopy and serial sections of the samples with light microscopy. KEY RESULTS Bract primordia arise first, followed by the stamen primordia in staminate flowers. Both bracts and stamens initiate unidirectionally, first on the abaxial side of the floral apex and later on the adaxial side, most likely due to the contact pressure imposed by the leaf primordium at the superior node. In pistillate flowers, bract primordia on the abaxial side were also initiated first. The configuration of buds at one node showed six patterns and each pattern included at least one vegetative bud, and flower buds were always accompanied by vegetative buds at the same node. CONCLUSIONS The initiation pattern of organs in the outer whorls of C. demersum flowers is distorted by mechanical pressure, resulting in the phyllotactic variation of staminate flowers. Vegetative buds are the main axillary buds with floral buds as accessory buds, which suggests that the shoot of C. demersum has been modified from a decussate phyllotaxis.

UNLABELLED • PREMISE OF THE STUDY Flowers of Sabiaceae diverge from basal eudicots in combining pentamery with superposed whorls of sepals, petals, and stamens and are therefore crucial in understanding origins of core eudicot flowers. Different hypotheses are tested using floral developmental evidence, whether the pentamerous flower is derived from a spiral, trimerous, or dimerous progenitor.• METHODS The floral development of two species of Sabia was investigated with the scanning electron microscope to understand their unusual floral morphology and the origin of pentamery.• KEY RESULTS The species show major developmental differences in their inflorescence morphology and organ initiation sequence. In S. limoniacea, flowers are subtended by a pherophyll preceding two prophylls, one of which encloses a younger flower; floral organs arise in a continuous spiral sequence without interruption between different organs. The ovary is oriented in an oblique-median position. In S. japonica, one prophyll replaces one of the sepals, and there is a disruption in the spiral sequence. As a result, the ovary is inserted more or less transversally.• CONCLUSIONS The flower of Sabiaceae is structurally best interpreted as derived from a trimerous progenitor, and a derivation from a dimerous or spiral progenitor is less likely. One organ of each median adaxial whorl is interpreted as lost (from K3+3 C3+3 A3+3 G3 to K3+2 C3+2 A3+2 G2). The number of sepals is variable as pherophylls, prophylls, and sepals cannot be distinguished by shape and intergrade with each other. The floral organization of Sabia is reminiscent of trimerous Ranunculales and supports an earlier divergence of Sabiaceae relative to Proteales.

The here presented compendium of papers on flower research is a contribution in answering the question “why are flowers what they are?” as presented by the recently created Flower Research Synectics network (FLO-RE-S). FLO-RE-S aims to bring plant scientists together to design and discuss joint research for the investigation of flower related questions. The inclusion of a diversity of perspectives and methodological approaches is crucial for the quality of the synthesis obtained. Investigations ranging from revealing the ontogeny to understanding the function of floral traits, and from experiments on floral genesis to the reconstruction of floral characters contribute to disentangling the nature and causes behind the floral shape.

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.

The Caryophyllales have the highest diversity in androecial patterns among flowering plants with stamen numbers ranging from 1 up to 4,000. Thanks to the recent progress in reconstructing the phylogeny of core Caryophyllales, questions of floral evolution, such as the origin and diversification of the androecium, can be readdressed. Caryophyllales are unique among core eudicots in sharing an androecial ring meristem or platform with centrifugal development of stamens and petals. Stamens are basically arranged in two whorls and evolution within the clade depends on the shift of either the antesepalous or the alternisepalous whorls to an upper position on the ring meristem and the reduction of the other. Four main developmental phenomena are responsible for the high diversity in androecial patterns: (1) the sterilisation of the outermost stamens through a division of common primordia; (2) the secondary addition of stamens by a centrifugal initiation of supernumerary stamens superimposed on a lower stamen number; (3) the pairwise displacement of alternisepalous stamens to the middle of the outer sepals and their potential fusion, or as part of a pluristaminate androecium; (4) the inversed sequence, reduction and loss of antesepalous stamens. Shifts in stamen numbers depend on pressures of the calyx and carpels and changes in the number of the latter. These patterns are expressed differently in the three main evolutionary lines of core Caryophyllales and are systematically relevant: (1) A basal grade of Caryophyllales, culminating with Caryophyllaceae, Amaranthaceae, Stegnosperma and Limeum, has the antesepalous stamens initiated in upper position on the ring meristem, and alternisepalous stamens are preferentially reduced. Among the antesepalous whorl there is a progressive loss of stamens following a sequence inversed to sepal initiation. Petaloid staminodes are formed by the radial division of outer stamens. (2) The raphide-clade and Molluginaceae are characterized by alternisepalous stamens in upper position on the ring meristem, with a trend to secondary stamen multiplication, and loss of antesepalous stamens. (3) The Portulacineae share the pattern of the raphide clade, but some taxa show shifts to an upper position on the ring meristem of either antesepalous or alternisepalous stamens, linked with secondary multiplications and reduction of either whorl. Different floral characters are plotted on a recent cladogram of Caryophyllales. The data show a consistent correlation between shifting carpel and stamen numbers independent of perianth evolution. Comparative data suggest that the basic androecium of Caryophyllales consists of two whorls of five stamens, linked with an absence of petals, and the evolution of the androecium is a combination of reductions and secondary multiplications of stamens with a highly predictive systematic value.

UNLABELLED PREMISE OF THE STUDY Caryophyllales are highly diverse in the structure of the perianth and androecium and show a mode of floral development unique in eudicots, reflecting the continuous interplay of gynoecium and perianth and their influence on position, number, and identity of the androecial whorls. The floral development of five species from four genera of a paraphyletic Molluginaceae (Limeum, Hypertelis, Glinus, Corbichonia), representing three distinct evolutionary lineages, was investigated to interpret the evolution of the androecium across Caryophyllales. • METHODS Floral buds were dissected, critical-point dried and imaged with SEM. The genera studied are good representatives of the diversity of development of stamens and staminodial petaloids in Caryophyllales. • KEY RESULTS Sepals show evidence of petaloid differentiation via marginal hyaline expansion. Corbichonia, Glinus, and Limeum also show perianth differentiation via sterilization of outer stamen tiers. In all four genera, stamens initiate with the carpels and develop centrifugally, but subsequently variation is significant. With the exception of Limeum, the upper whorl is complete and alternisepalous, while a second antesepalous whorl arises more or less sequentially, starting opposite the inner sepals. Loss or sterilization of antesepalous stamens occurs in Glinus and Limeum and is caused by altered carpel merism and inhibition by sepal pressures. • CONCLUSIONS Outer stamens of Hypertelis correspond with petaloids of Caryophyllaceae and suggest that staminodial petaloids and outer alternisepalous stamens are interchangeable in the Caryophyllales. We emphasize a switch in the position of first formed stamens from antesepalous to alternisepalous following the divergence of Limeum; thus stamen position is an important synapomorphy for the globular inclusion clade.

International audience; Premise of the Study: Zygomorphy has evolved multiple times in angiosperms. Near-actinomorphy is the ancestral state in the early diverging eudicot family Papaveraceae. Zygomorphy evolved once in the subfamily Fumarioideae from a disymmetric state. Unusual within angiosperms, zygomorphy takes place along the transverse plane of the flower. Methods: We investigated floral development to understand the developmental bases of the evolution of floral symmetry in Papaveraceae. We then assessed the expression of candidate genes for the key developmental events responsible for the shift from disymmetry to transverse zygomorphy, namely CRABSCLAW for nectary formation (PAPCRC), SHOOTMERISTEMLESS (PAPSTL) for spur formation, and CYCLOIDEA (PAPCYL) for growth control. Key Results: We found that an early disymmetric groundplan is common to all species studied, and that actinomorphy was acquired after sepal initiation in Papaveroideae. The shift from disymmetry to zygomorphy in Fumarioideae was associated with early asymmetric growth of stamen filaments, followed by asymmetric development of nectary outgrowth and spur along the transverse plane. Patterns of PAPSTL expression could not be clearly related to spur formation. PAPCRC and PAPCYL genes were expressed in the nectary outgrowths, with a pattern of expression correlated with asymmetric nectary development in the zygomorphic species. Additionally, PAPCYL genes were found asymmetrically expressed along the transverse plane in the basal region of outer petals in the zygomorphic species. Conclusion: Genes of PAPCRC and PAPCYL families could be direct or indirect targets of the initial transversally asymmetric cue responsible for the shift from disymmetry to zygomorphy in Fumarioideae.

Nine species of wood lawn neophytes (Grassameneinkommlinge) have been reported from the parkland of mansion houses in the Scottish Borders. These species have most probably been introduced during the nineteenth century when laying out lawns and parkland studded with trees in the style of English landscape gardens. Similar occurrences have been reported from several northwest European countries, but the presence of such neophytes in Britain is not well known and it is poorly documented. We have found evidence that Poa nemoralis seed ‘for growing under trees’ was also traded in Scotland; moreover, the particular wood lawn neophytes reported prove that the seed mixtures for shaded lawns must have come from south and central Germany, as that is the provenance of all the species found. These mostly grass-like neophytes often occur together, but it is not always clear whether a particular species was deliberately added to the seed mixtures or whether it was merely a seed impurity. Be that as it may, the...

The flower development of a number of taxa with either unclear or only recently clarified phylogenetic positions in the order Ericales has remained uninvestigated for a long time because of the unavailability of material. Two genera, traditionally placed in the Primulaceae but often described as aberrant, are Ardisiandra, with three African species, and the monotypic East Asian Stimpsonia. We investigated the floral ontogeny of Ardisiandra wettsteinii and Stimpsonia chamaedryoides in order to improve the understanding of these species and to find support for their present position within Myrsinaceae. Stamens and petals develop from common primordia as in all primuloid taxa, but petal development is much delayed in comparison to several other Myrsinaceae s.l. Sepal initiation, common stamen-petal primordia, insertion of ovules, extensions of placental tips, and type of nectary are compared with other taxa of the primuloid clade. The identified putative synapomorphies extend the morphological basis for the ...

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 ...

The almost cosmopolitan distribution of Samolus valerandi is unique in the genus Samolus L. (Samolaceae), which also includes 12–15 taxa with distributions restricted to smaller areas of the Southern Hemisphere. Recent molecular phylogenetic studies based on chloroplast and nuclear DNA sequences showed that the widespread S. valerandi and the North American S. parviflorus are both part of a strongly supported clade, together with the North American S. vagans, S. spathulatus, and S. latifolius. To better understand the origin, distribution, and diversification of S. valerandi and to clarify the relationships within this clade, we performed molecular phylogenetic analyses based on the plastid trnS-G intergenic spacer and the nuclear ribosomal ITS region. We have also sought further support for relationships by examining flower and leaf characters. On the basis of new results, we propose that S. valerandi, S. parviflorus, and S. vagans are considered as part of a widespread “species complex”, with its centre of diversity in North America. No clear vicariance patterns were found regarding the phylogeography of S. valerandi, which thus seems to have dispersed secondarily to various places around the world, possibly as a result of human activities.

The floral ontogeny of two species of Knema and one of Horsfieldia was examined and described using scanning electron microscopy. The perianth is trimerous with three tepals arising in succession. Pistillate flowers have a rounded floral apex with a convex top. The single carpel primordium is initiated along the margin of the bud and develops a plicate shape with an apical bilobed stigma. In staminate flowers, the floral apex is broadly hemispherical with a somewhat three-sided shape. Several anther primordia are initiated almost simultaneously around the margin of the floral apex. In Horsfieldia, stamens extend laterally in antetepalous groups, whereas, in Knema, anthers form two whorls. The alternitepalous stamens were found to be different from the antetepalous stamens, which are pressed within a limited space. The anther primordia remain adnate to the receptacle and grow longitudinally, producing a pair of microsporangia. The central area of the floral apex persists as an undifferentiated residuum without any trace of a gynoecium. Myristicaceous anthers are basically homologous, although the number of anthers, pollen sacs and shape of the androecium are variable. The evolution of the androecium is discussed in the family, with opposing possibilities for reductions and increases in anther number in Myristicaceae. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 164, 42–52.

European representatives of Apium sensu lato (Apiaceae), and Apium prostratum and Naufraga balearica, were studied with morphological, fruit anatomical, and palynological methods. Morphometric data were compared with phylogenetic results from previous molecular studies. This confirms that most of the European Apium species belong to a separate group corresponding to the previously named genus Helosciadium. All these species had previously been formally named as Helosciadium species, except for the new combination Helosciadium bermejoi, which is formally described here. Molecular studies place Apium prostratum and Naufraga balearica close to Apium graveolens, the type species of Apium. Our morphometric results show similarities of Naufraga with H. bermejoi, but fruit anatomy distinguishes it both from Helosciadium and from A. graveolens/prostratum. The placement of Cyclospermum leptophyllum in a separate genus is confirmed. Diagnostic keys to the genera and Helosciadium species, and an annotated checklist are given.

Floral development and anatomy were investigated in the monotypic Aextoxicaceae (one species: Aextoxicon punctatum), one of two families of Berberidopsidales, to understand its putative relationship with Berberidopsidaceae and clarify floral evolution in basal core eudicots. Aextoxicon is dioecious, with unisexual flowers that display a late abortion of male and female organs in the respective genders. Flowers are pentamerous or hexamerous and are enclosed by a calyptra derived from the congenital fusion of two bracteoles. Initiation sequence and number of sepals, petals, and stamens are variable and mostly spiral, without clear transition between organ categories, and a single carpel initiates without evidence of a second carpel. The ovary contains two apical‐marginal ovules. Floral anatomical data suggest that the nectaries are receptacular in nature. Aextoxicon displays floral characters found in basal angiosperms, such as a unicarpellate gynoecium, an interrupted hoodlike outer integument, little diff...

Flowers of Santalales remain largely unexplored with several questions of homology unanswered despite the large size of the order. Morphological and ontogenetic floral studies have the potential to identify new informative characters. We studied floral development in species of Loranthaceae, Santalaceae, Opiliaceae, and "Olacaceae" with scanning electron microscopy to clarify the origin and evolution of the perianth in Santalales. The perianth is either dichlamydeous or when monochlamydeous interpreted as sepals, petals, or tepals. A girdling calyculus of debatable origin is found in some clades. We show that species of Diogoa and Heisteria in "Olacaceae" have a dichlamydeous perianth, unlike Olax in which the calyx is replaced by a calyculus. The calyculus arises by development of two lateral primordia, supporting the hypothesis of bracteole origin. A calyculus with similar development is present in species of Loranthaceae and possibly of Opiliaceae, suggesting a position of Olax closer to these families than to traditional genera of "Olacaceae". The monochlamydeous perianth in Santalaceae is shown to correspond to petals of other members of Santalales. Flower ontogenetic evidence suggests a repeated loss of the calyx, replacement by a calyculus, and further loss, leading to monochlamydeous perianths in Santalaceae.

Seventeen morphological characters are described and plotted on a phylogeny of the eudicots. The distribution of perianth characters demonstrates that the currently held view that petals originated from stamens in the core eudicots is not consistent with the predominance of bract-derived petals (bracteopetals). Petals in the core eudicots have the same morphological affinities and structure as sepals or bracts, with a few notable exceptions. Depending on the most likely topology, Berberidopsidales may represent the plesiomorphic perianth condition in the core eudicots, giving rise to pentamerous flowers with sepals and petals of a similar tepaline origin. Within the core eudicots several divergent trends have led to a wide variety of perianth morphologies involving to different degrees the presence of a calyx and corolla. Different factors contribute to the development of a biseriate perianth, including the upward shift of bracts and their absorption in the flower and a progressive differentiation of tepals through shifts in petaloidy. A number of correlations in perianth evolution are highlighted, such as petaloid sepals linked with loss of petals and presence of a hypanthium, a reversal to tepal-like petals with secondary polymery in the androecium and gynoecium, or the loss of sepals linked with the development of stamen-petal tubes. The relationship between petal morphology and the molecular basis for petaloidy is discussed.

The structure and anatomy of mature flowers of four species of Meliosma is investigated using scanning electron and light microscopy. The vasculature of the flower, including the structure of the gynoecium, is described in detail. The mechanism of stamen maturation and pollen release is illustrated and discussed. The existence of an explosive pollination mechanism is questioned for at least part of the species. Flowers are proterandrous and fertile stamens are kept spatially separate from the style by a ring of large staminodes. Anthers are disporangiate by the loss of the adaxial pollen sacs. During maturation the filament bends progressively outwards and releases the pollen on the extension of the connective that acts as a secondary pollen presentation system. The nectary has five appendages topped with stomata secreting abundant nectar. The relationships of Sabiaceae are discussed relative to other early diverging eudicots. The significance of Sabiaceae as an isolated clade is highlighted, although some features point to a link with Menispermaceae.

Flower developmental studies are a complement to molecular phylogenetics and a tool to understand the evolution of the angiosperm flower. Buds and mature flowers of Meliosma veitchiorum, M. cuneifolia, and M. dilleniifolia (Sabiaceae) were investigated using scanning electron microscopy to clarify flower developmental patterns and morphology, to understand the origin of the perianth merism, and to discuss the two taxonomic positions proposed for Sabiaceae, among rosids or in the basal grade of eudicots. Flowers in Meliosma appear pentamerous with two of the five sepals and petals strongly reduced, three staminodes alternating with two fertile stamens opposite the small petals, and a two-carpellate gynoecium. The flower development in Meliosma is spiral without distinction between bracteoles and sepals. Because of this development, sepals, petals, and stamens are almost opposite and not alternating as expected in cyclical pentamerous flowers. In four-sepal flowers the direction of petal initiation is reversed. The symmetry of the flower appears to be transversally zygomorphic, although this is hidden by the almost equal size of the larger petals. Evidence points to a unique pentamerous origin of flowers in Meliosma, and not to a trimerous origin, as earlier suggested, and adds support to multiple origins of pentamery in the eudicots.

Floral development and inflorescence structure within Streptocarpus and Saintpaulia were investigated using Scanning Electron Microscopy (SEM). We discuss the structure and development of the pair-flowered cyme and the floral ontogeny found in the Gesneriaceae in a phylogenetic context with particular reference to an East African clade of Streptocarpus and Saintpaulia. Current phylogenetic hypotheses divide the caulescent East African Streptocarpus species into two distinct clades, in relation to which the position of Saintpaulia is not yet clear. Variation in the branching of the inflorescence showed phylogenetic significance and included dichasial, monochasial and unbranched patterns. In four of the East African Streptocarpus species sampled a single lateral bracteole was present on the first to third axes, after which the inflorescence was ebracteolate. Our results indicate that there may be some link between bracteole suppression and an alteration in the order of sepal initiation. The loss or suppression of lateral bracteoles also appears to result in the precocious development of the lateral cyme meristem.

Floral morphology of 16 species of Gunnera representing all six subgenera is examined and described using scanning electron microscopy (SEM). The evolution of 19 flower morphological characters is discussed. Eight of these characters are optimized on a current phylogenetic tree. Character evolution tends to be generally continuous over different clades and several parallel evolutionary patterns of floral reduction can be identified within the family. At one extreme stand species such as G. manicata and G. perpensa with mainly bisexual flowers bearing well-developed sepals and petals, and at the other stand species such as G. magellanica and G. herteri with perianthless staminate flowers, and pistillate flowers with only gynoecia and sepals. In between one finds a range of flower morphologies, bisexual or not, with petals and sepals present or absent, or discernable as reduced organs. Character-state reconstruction and morphological evidence suggest that flowers in Gunneraceae were bisexual in origin with a reduction leading to simple unisexual flowers. Among the examined characters, absence of reduced organs in the other gender, spathulate petals in the staminate flower, long styles, and the presence of well-developed bracts are typical for species of subg. Milligania. Basally connected sepal lobes with a strongly swollen base and reduced blade is found in all species of Panke and in G. magellanica (subg. Misandra). Selected synapomorphies are consistent with the deep phylogenetic division of Gunnera between the New and Old Worlds.

A cladistic analysis is performed using 94 morphological and biochemical characters for 42 genera to compare a phylogeny based on morphological data with those obtained using different genes (rbcL, atpB, 18S RNA, matK) or their combination with morphological data, and to understand the floral evolution within the expanded Brassicales (Capparales) relative to Sapindales and Malvales. The tree produced with morphological data is congruent with those obtained from macromolecular studies in obtaining a well-supported glucosinolate-producing clade and an expanded Sapindales. The combined analysis of the morphological and molecular characters is generally well resolved with support for many of the relationships. The inclusion of the fossil taxon Dressiantha demonstrates the value of inserting fossil evidence in phylogenetic analyses. However, the fossil appears to be related to the Anacardiaceae and not to the Brassicales. The core Brassicales are well supported by a number of synapomorphies, although the internal position of Tovariaceae and Pentadiplandraceae is not well resolved. Emblingiaceae appears to be related to Bataceae and Salvadoraceae. Several significant morphological characters are mapped on the combined trees and their evolutionary significance is discussed. Within Brassicales and Sapindales several well supported clades can be recognized which merit ordinal or subordinal status, putting the present orders at a higher level; these include: Tropaeolales, Setchellanthales, Batidales, Brassicales (Brassiciflorae), Burserales, Sapindales and Rutales (Sapindiflorae). The present scheme of affinities within the Brassicales corresponds well with a gradual morphological evolution in the order. © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society, 2006, 151, 453–494.

The floral ontogeny of the Spurge olive (Cneorum tricoccon L.) is studied by means of scanning electron microscopic observations. Special attention is paid to the sequence of initiation of the floral parts, the occurrence of septal cavities, and the development of the nectariferous tissue. The nectary disc arises as a receptacular outgrowth below the ovary and independently from stamen development. By the extensive growth of this voluminous androgynophore, stamen filaments become enclosed by nectary tissue and as a result, they are seated in pits between the lobes of the disc. Between ovary and style, three lobes are present, which are covered with stomata – their function is unknown. The significance of the unusual trimery of the flower is discussed. Floral developmental evidence supports a Rutalean affinity, although more ontogenetic investigations are needed in Rutaceae, subfamily Spathelioideae.

Recent molecular phylogenetic studies have shown that the Gunnerales, including Gunnera and Myrothamnus, form a clade, sister to other core eudicots. This systematic position puts Gunnera in a pivotal position regarding the evolution of morphological characters in eudicots. In particular, the dimerous flower organization of Gunnera has recently been considered precursor to the pentamerous condition found in most core eudicots. In order to understand the role of Gunnera in the flower evolution of core eudicots, new detailed studies of the flowers of Gunnera are needed. In this study, the flower ontogeny and morphology of Gunnera monoica and G. dentata as well as of G. macrophylla were studied with SEM. The new observations are compared with previous studies of G. manicata and G. herteri. The first four species have dimerous perfect or staminate flowers with two small median sepals, followed by two large petals opposite the two stamens. In G. herteri, the staminate flowers are reduced to single stamens. In ...

The pollen of 30 taxa (27 species, one subspecies and two varieties) in two genera, viz Polygonum s. str. and Polygonella was investigated with LM and SEM, and some selected taxa with TEM. In all genera investigated the pollen is prolate to spheroidal, and the aperture is mostly tricolporate, rarely panto-hexacolporate (especially Polygonum section Polygonum). The exine sculpturing pattern is the most variable feature. Three types of exine can be recognized. Type 1 (Avicularia-Type, sensu Hedberg) - All species of section Polygonum and section Tephis share the smooth tectate exine with spinules, sometimes the surface is more or less rough (Polygonum afromontanum in section Tephis). Type 2 (Pseudomollia-Type, sensu Hong) - Pollen of Polygonum molliaeforme (section Pseudomollia) has the exine, which is verrucose on both poles and nearby the mesocolpium, and mostly psilate around the ectoaperture. Type 3 (Duravia-Type, sensu Hedberg) - Pollen grains of Polygonum section Duravia and Polygonella have the exine which is semitectate-reticulate at the mesocolpium and the poles, and rugulate/reticulate or sometimes foveolate with microspinules around the ectoapertures. The pollen grains in four taxa (viz Polygonum section Pseudomollia, P. section Duravia and genus Polygonella) have a well-marked dimorphism of the ektexine, which is considered to be a synapomorphic condition. The differences of pollen grain between the genus Polygonella and Polygonum section Duravia are almost non existent and clearly interrelated. It is therefore postulated that the similarity in pollen of both taxa is not the result of convergency, but is interpreted as a homology. It is noteworthy that the pollen of Polygonum molliaeforme (section Pseudomollia) appears as intermediate between the Avicularia-type and the Duravia-type, and is well supported the value of separated section for its own. Additionally, in TEM, some exine ultrastructures (e.g. columellae, foot layer, endexine) appear to be valuable characters for comparison between/among taxa. The systematic potentialities of the pollen data of the studied taxa at various systematic levels are also discussed.

Molecular phylogenies have associated Bataceae with Salvadoraceae and Koeberliniaceae in an expanded Brassicales. Despite a long taxonomic history, the knowledge of the flower of Batis is still fragmentary. The floral development of pistillate and staminate inflorescences of Batis maritima was investigated to understand homologies of floral structures and to discuss the phylogenetic position of Bataceae within the Brassicales. There has been considerable controversy in the past about the male flower, especially on the nature of the petals and the tubular structure enclosing the flower. Developmental evidence confirms that the male flower is built on a basic tetramerous bauplan and that the tubular structure is derived from four congenitally fused sepal lobes with the three anterior lobes highly reduced. The development of petals and stamens is unidirectional, and the androecium initiates the median stamens before the lateral stamens, suggesting the existence of two whorls. The pistillate flowers are reduced to the bare minimum with two transversal carpels enclosed by a bract. Partial inflorescences function as a swollen dispersal unit. The vestigial stipules probably represent colleters and are not homologous with true stipules. Several characters of Batis are reminiscent of the Brassicaceae, although a link with Salvadoraceae and Koeberliniaceae cannot be excluded.

The floral development and anatomy of Dirachma has been investigated with SEM and LM to discuss the relationship of Dirachmaceae with putative sister taxa (e.g. Rhamnaceae, Malvaceae, Barbeyaceae, Elaeagnaceae) on the basis of morphological synapomorphies. Flowers are initiated in axillary position on terminal branches. An epicalyx consisting of six to eight bracteoles surrounds the valvate calyx. Petal initiation is strongly retarded and primordia arise independently opposite the stamen primordia. The carpels arise independently and become weakly fused at the base; a single ovule develops in an axile position. A hypanthium develops by interprimordial growth between petals and stamens. Nectaries arise in a pouch and are covered with trichomes positioned on a protuberance at the base of the petal. It is suggested that the solitary flowers are derived from compound cymose inflorescences. Comparison between Dirachma and species of Rhamnaceae demonstrates striking similarities in floral structure and anatomy. However, several characters are unique to Dirachma and support a family Dirachmaceae separate from Rhamnaceae.

Homeosis is the result of a developmental process where attributes of one structure are transferred to the position normally occupied by a different structure. The importance of homeotic mutations in the evolution of flowers and their impact on the whole pollination strategy is discussed from a morphological perspective, with special reference to the development of floral organs and the underlying genetics. Three case studies are presented where transformations of organs in flowers have important evolutionary implications, and these are related to the genetic background that is causal for these changes. I hypothesize that petals in the Rosaceae are derived from stamens through homeosis. The petals usually occupy an apical position in a complex multistaminate androecium. Evidence is derived from the similar primordial morphology of petals, their occasional replacement by stamens, obhaplostemonous androecia without petals, and the position of the family next to Rhamnaceae and Urticales. It is postulated tha...

The evolution of selected characters of the perianth, androecium, and gynoecium was reconstructed on a modification of the recent three‐gene topology for angiosperms to address patterns of evolution in the flowers of basal angiosperms. The reconstructions indicate that the patterns of perianth and stamen phyllotaxis are usually, but not always, closely associated. The attainment of a stable perianth and stamen phyllotaxis preceded stability in the gynoecium. There are several surprising reversals from whorled to spiral phyllotaxis in different clades. The developmental mechanisms responsible for changes in stamen number have rarely been evaluated in basal angiosperms, in contrast to the eudicots. Our reconstructions reveal a close relationship between a whorled phyllotaxis, a reduction of the number of stamen whorls, and stamens in double (paired) positions. Staminodes appear frequently in different lineages. A strict distinction between a sepal‐derived and a staminodial, stamen‐derived perianth is not al...

Eurycorymbus is an unusual monotypic genus of Sapindaceae endemic to China. The floral organogenesis of E. cavaleriei has been investigated with the light and scanning electron microscope to clarify its floral characters and its uncertain systematic position. Eurycorymbus cavaleriei possesses several unique characteristics in Sapindaceae. Flowers are unisexual. Sepals initiate in a spiral sequence, followed by five alternating petals which resemble sepals at maturity. The sequential initiation of eight stamens partly overlaps with that of the petals. Three carpellary lobes are simultaneously demarcated and merge gradually to form a tricarpellate ovary. Mature stamens of male flowers have long and smooth filaments, which are folded in buds. In female flowers only one or two ovules per ovary develop into seeds. The extrastaminal nectary forms doubly scalloped lobes. Symmetry changes from oblique monosymmetry at a mid-developmental stage to polysymmetry at maturity. It is suggested that monosymmetry might precede polysymmetry in the evolution of Sapindaceae.