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Carpinus betulus (Betulaceae).-A-H. Female flowers from a single tree showing intra-individual variability of sepal formation, with corresponding sepal formula of the visible side indicated at upper right.-I-K. Floral diagrams with corresponding sepal formula of one side of the flower indicated. Magnification bars: A-H 5 0.5 mm.
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Floral architecture and floral organ shape are interrelated to some extent as can be seen in the diversity of extant angiosperm groups. The shape of fragmentary fossil material, such as single organs, may therefore give hints for the reconstruction of the architecture of a flower. This study is partly a review and partly provides original material...
Citations
... Imprinted shapes are the shapes caused by pressure from contiguous organs. Such pressures can change the autonomous shape of an organ that would develop without physical influence from adjacent organs (Endress 2008). Similar patterns can be observed in Astragalus (Fabaceae) species, in which the pressure of the bracts influences the sequence of sepal initiation, with the first sepals appearing preferentially where pressure is lower (Naghiloo et al. 2012). ...
The genus Mimosa L. (Leguminosae; Caesalpinioideae; mimosoid clade), comprising more than 500 species, is an intriguing genus because, like other members of the mimosoid clade, it presents an enormous variation in floral characteristics and high merism lability. Thus, this study aimed to elucidate the floral development and identify which ontogenetic pathways give rise to merism variation and andromonoecy in Mimosa caesalpiniifolia, M. pudica, M. bimucronata, and M. candollei. Floral buds at various stages of development and flowers were collected, fixed, and processed for surface analysis (SEM). The development of the buds is synchronous in the inflorescences. Sepals appear simultaneously as individualized primordia in M. caesalpiniifolia and in reversed unidirectional order in M. bimucronata, with union and formation of an early ring-like calyx. Petal primordia appear in unidirectional order, with a noticeably elliptical shape in M. caesalpiniifolia. The wide merism variation in Mimosa results from the absence of organs from inception in the perianth and androecium whorls: in dimerous, trimerous, or tetramerous flowers, the additional organs primordia to compose the expected pentamerous flowers are not initiated. The haplostemonous androecium of M. pudica results from the absence of antepetalous stamens from inception. In the case of intraspecific variations (instabilities), there is no initiation and subsequent abortion of organs in the events of reduction in merosity. In addition, extra primordia are initiated in supernumerary cases. On the other hand, staminate flowers originate from the abortion of the carpel. Mimosa proved to be an excellent model for studying merism variation. The lability is associated with actinomorphic and rather congested flowers in the inflorescences. Our data, in association with others of previous studies, suggest that the high lability in merism appeared in clades that diverged later in the mimosoid clade. Thus, phylogenetic reconstruction studies are needed for more robust evolutionary inferences. The present investigation of ontogenetic processes was relevant to expand our understanding of floral evolution in the genus Mimosa and shed light on the unstable merism in the mimosoid clade.
... Floral shape, organ positions, and sequence of initiation are determined by the positions of neighbouring structures and their interactions (regardless the nature) with the developing flower (Endress 2008, Remizowa et al. 2013, Bull-Hereñu et al. 2022. Female flowers are strongly flattened in the transversal plane; this is due to the pressure of the bud scales, as well as the transversal position of the carpel backs, which occupy nearly all the space inside the floral bud. ...
... Sepals during floral development and in anthetic flowers do not have any adaptive function in A. negundo. Probably, the loss of their functional significance led to a decrease in their size and an increase in the diversity of position and number (Endress 2008). However, in female flowers, the positions and number of sepals are more stable. ...
Acer negundo L. is a wind-pollinated, dioecious tree that occasionally produces flowers with rudiments of the opposite sex. Both the male (staminate) and female (pistillate) flowers possess only two whorls: sepals and stamens or carpels, the arrangement of which is disputed. Here we present data on inflorescence and floral development, pollen fertility in staminodes and the diversity of male and female flowers. We found that the merism of male flowers is unstable, and the numbers of stamens and sepals vary independently. The different floral groundplans always occur within the inflorescences of the same generative shoot. The development of a flower begins with the initiation of sepals, but in female flowers, sepals are initiated sequentially and remain of different sizes, whereas in male flowers, sepals are initiated almost simultaneously and are equal. After the appearance of stamen primordia or carpel primordia, a part of the undifferentiated meristem remains. This unused meristem can be involved in producing staminodes or pistillodia. Both unisexual and (partly) bisexual flowers are found in the same inflorescence. Staminodes are either completely sterile or produce some amount of viable pollen. These features indicate the possibility of functional bisexuality in A. negundo.
... Changes of floral symmetry occur during development in many taxa including monocots (summarized in Endress 1999, 2008, 2012, Remizowa et al. 2013b. Symmetry of flo wers in early development is influenced by surrounding parts of the inflorescence. ...
Pendent sessile flowers of Chamaelirium japonicum (Willd.) N. Tanaka appear zygomorpic, but they do not possess a bilateral symmetry. The flowers are subtended by a vestigial bract and lack a bracteole. The perianth consists of two small tepals on the abaxial side of the flower and four large tepals, none of which is median. Because the short tepals belong to different whorls, there is no symmetry plane. Despite the absence of a bracteole, the shape of the floral meristem before peri anth inception resembles that of bracteolate monocot flowers. At early stages, all six tepals are equal in shape and size, and the flower is actinomorphic. The differ ence between the dorsal and ventral sides and the pendent nature of the flower become expressed during the gynoecium development. The absence of median organs allows to avoid collision of floral organs with the flower-subtending bract during flower curvature. Species of Chamaelirium reveal a set of different flower groundplans, which makes the genus a perfect model to investigate evolutionary changes in flower symmetry accompanied by differential tepal reduction.
... Thus, early in the floral development, the carpels are parallel to the floral axis, while petals and stamens are perpendicular to it. Generally, the emergence of the floral organs follows a sequence that is typical of their taxonomic group and is submitted to the physical conditions imposed by the floral meristem surroundings (Endress 2008(Endress , 2011Ronse De Craene 2018). The outer organs usually appear before the inner ones in most angiosperms (Remizowa 2019). ...
The floral diversity of Melastomataceae is stunning and clearly expressed in sepal and stamen structure and in the position of the ovary. Comparative developmental studies are effective in order to understand these variations because they reveal the often-enigmatic origin of the structures. The diverse calyx structure originates from variations in the degree of union between the sepals. The contort corolla aestivation, widespread in the family, is influenced by the floral architecture. Stamen size and shape depend on the space available in the floral bud after the growth of the perigynous hypanthium that may cause the delay in stamen emergence and flexion. Dimorphic stamens originate from differences in their developmental time and position. Prolonged connectives and most of their appendages are formed late during floral development. Ontogeny also explains the decrease or increase in organ number. The intercalary meristems can promote the formation of a hypanthium associated with the gynoecium, and their extension is responsible for the gradual variation in ovary position. These meristems also act on the development of a perigynous hypanthium. Thus, intercalary meristems play an important role for floral diversification in Melastomataceae. The potential of comparative floral development is wide and is illustrated here through several examples in this family.
... Such space can be readily occupied by the growing stamen (e.g., Miconia dodecandra, Fig. 4d-f; Miconia melastomoides Fig. 5f-i). This is probably a case of "imprinted shape", as called by Endress (2008), and opposed to "autonomous shape". The imprinted shape of an organ is the result of pressure exerted by adjacent organs, which act as molds for the still-expanding structure. ...
The androecium of Melastomataceae presents notable modifications in its merosity, morphology between whorls and in prolonged connectives and appendages. We carried out a comparative study of six Melastomataceae species to shed light on the developmental processes that originate such stamen diversity. The development of stamens was studied using scanning electron microscopy and histological observations. The stamens of all species studied have a curved shape because they emerge on a plane displaced by the perigynous hypanthium. They are the last flower organs to initiate and therefore their growth is inwards and towards the floral center. Despite the temporal inversion between carpels and stamens in Melastomataceae, the androecium maintains the centripetal pattern of development, the antepetalous stamens emerging after antesepalous stamens. The isomerous androecium can be the result of abortion of the antepetalous stamens, whereas heterostemony seems to be caused by differences in position and the stamen development time. Pedoconnectives and ventral appendages originate from the basal expansion of the anther late in floral development. The delay in stamen development may be a consequence of their dependence on the formation of a previous space so that they can grow. Most of the stamen diversity is explained by the formation of the connectives and their appendages. The formation of a basal-ventral anther prolongation, which culminates in the development of the pedoconnective, does not differ from other types of sectorial growth of the connective, which form shorter structures.
... This means that systematic differences exist between the left and right halves: for each fall the left margin is situated inside and the right margin outside the neighboring falls in the bud (Figure 1b), which requires an inherent morphogenetic difference between the left and right sides of each fall. Also, as a consequence, the right margin of each fall is exposed to the outside, whereas the left margin is not, which may have observable morphological effects (Endress, 2008). Whether as a result of an inherent asymmetry between the left and right sides of each fall or due to the difference in exposure, the observed asymmetries in the shapes of individual falls (Figure 3b,f) are likely to be related to their contort aestivation. ...
Directional asymmetry is a systematic difference between the left and right sides for structures with bilateral symmetry or a systematic differentiation among repeated parts for complex symmetry. This study explores factors that produce directional asymmetry in the flower of Iris pumila, a structure with complex symmetry that makes it possible to investigate multiple such factors simultaneously. The shapes and sizes of three types of floral organs, the falls, standards, and style branches, were quantified using the methods of geometric morphometrics. For each flower, this study recorded the compass orientations of floral organs as well as their anatomical orientations relative to the two spathes subtending each flower. To characterize directional asymmetry at the whole-flower level, differences in the average sizes and shapes according to compass orientation and relative orientation were computed, and the left-right asymmetry was also evaluated for each individual organ. No size or shape differences within flowers were found in relation to anatomical position; this may relate to the terminal position of flowers in Iris pumila, suggesting that there may be no adaxial-abaxial polarity, which is very prominent in many other taxa. There was clear directional asymmetry of shape in relation to compass orientation, presumably driven by a consistent environmental gradient such as solar irradiance. There was also clear directional asymmetry between left and right halves of every floral organ, most likely related to the arrangement of organs in the bud. These findings indicate that different factors are acting to produce directional asymmetry at different levels. In conventional analyses not recording flower orientations, these effects would be impossible to disentangle from each other and would probably be included as part of fluctuating asymmetry.
... In contrast the shape of the inflorescence meristem of Fritillaria imperialis is fasciated (an oval shape; Figures 8F-H). While the meristem is fasciate the mature inflorescence stem is round, due to shape imprinting (Endress, 2008; Figure 1A). Organ primordia are initiated spirally with little internodal elongation between organs ( Figure 8I). ...
Inflorescence structure is very diverse and homoplasious, yet the developmental basis of their homoplasy is poorly understood. To gain an understanding of the degree of homology that these diverse structures share, we characterize the developmental morphology and anatomy of various umbellate inflorescences across the monocots and analyzed them in an evolutionary context. To characterize branching order, we characterized the developmental morphology of multiple inflorescences with epi-illumination, and vascular anatomy with Laser Ablation Tomography, a novel high-throughput method to reconstruct three-dimensional vasculature. We used these approaches to analyze the umbellate inflorescences in five instances of presumed homoplasy: in three members of the Amaryllidaceae; in three members of the Asparagaceae, including a putatively derived raceme in Dichelostemma congestum; in Butomus umbellatus (Alismataceae), in Tacca chantrieri (Dioscoreaceae), and in umbellate structure in Fritillaria imperialis (Liliaceae). We compare these with racemes found in three members of the subfamily Scilliioideae (Asparagaceae). We find there are three convergent developmental programs that generate umbellate inflorescences in the monocots, bostryx-derived, cincinnus-derived and raceme-derived. Additionally, among the bostryx-derived umbellate inflorescence, there are three instances of parallel evolution found in the Amaryllidaceae, in two members of Brodiaeoideae (Asparagaceae), and Butomus umbellatus, all of which share the same generative developmental program. We discuss the morphological modifications necessary to generate such complex and condensed structures and use these insights to describe a new variant of metatopy, termed horizontal concaulesence. We contextualize our findings within the broader literature of monocot inflorescence development, with a focus on synthesizing descriptive developmental morphological studies.
... How can mechanical forces be considered as part of an ontogenetic process in a plant? Seen from a broad perspective, every growth process of a plant organ, and in particular, of a flower, involves the occurrence of mechanical forces at the tissue level such as stretching, compression, torsion, ripping, and so on [6,7]. Something that might sound obvious and spurious in the first place acquires biological interest when it is noticed that for a particular floral phenotype to be expressed or achieved, specific internal mechanical events are required throughout ontogeny ( Figure 1). ...
... A tight pressure of the inflorescence bracts can mold monosymmetric lateral buds ( Figure 5B,C), as seen in the flowers of Euptelea (Eupteleaceae, Figure 6A) [7,21,22], Notobuxus (Buxaceae, Figure 6B) [23] or Drymis (Winteraceae, Figure 6C,D) [24]. Similarly, the tetragonal lateral flowers that occur in Bataceae and Salvadoraceae seem to be a direct consequence of the compression of their floral meristem between bract and inflorescence axis [25,26]. ...
... The pressure exerted by external organs mold the shape of the organs they cover. This closely relates to the concept of "imprinted shape" by Endress [7,[89][90][91], in which floral parts are shaped by adjacent organs during development leaving pressure marks recognizable on the tissue [7]. ...
Mechanical forces acting within the plant body that can mold flower shape throughout develop-ment received little attention. The palette of action of these forces ranges from mechanical pres-sures 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 to-wards the shaping of the mature flower.
... Endress [9] describes the stamens of Cananga odorata flowers as having cuneate forms with a large apex and short filaments. A single Cananga odorata flower has numerous stamens that are densely arranged spherically on the flower apex. ...
Cananga odorata is a native plant in the Indonesian archipelago. The flowers are often used to produce essential oils with many uses and a distinct fragrance. This study aims to observe each stage of the Cananga odorata flower development. The flowers were obtained from a home garden in Pasar Minggu, South Jakarta, from November 2020 until January 2021. Further observations of the stamen and pistil developments were conducted using Dino-Lite Edge Digital Microscope AM4115 Series. The results show that Cananga odorata flower development can be categorized into bud, display-petal, initial-flowering, full-flowering, end-flowering, and senescence stages. The flowers require 35 days to develop from bud stage to flower senescence. Stamens and pistils also develop primarily during the bud stages and mature after flower anthesis. Flower mutants were also found and may be caused by a mutation in the flower’s homeotic genes. Each different stages of flower development show a different morphological change in the flower perianth and reproductive organs. A discrepancy of flower morphology within each stage, especially those seen during the anthesis stages, might imply a variation in the flower’s internal factors.
... In the Heptapleurum spp. with the most Table 3. Carpel size measured as stigma width in developing female flowers of Pennantia corymbosa, normalized to the size of the widest stigma in each flower. The carpels are labelled with letters A-C in a counterclockwise direction beginning from the carpel with the smallest stigma (Fig. 18C) Endress, 2008). The calyx of P. corymbosa is represented by an unvascularized collar beneath the level of petal attachment without any traits of individual sepals. ...
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. ADDITIONAL KEYWORDS: anatomy-carpel dimorphism-development-evolution-gynoecium-New Zealand-pollen dimorphism-pseudomonomery-recaulescence-vasculature.
