Sapindales is a monophyletic order within the malvid clade of rosids. It represents an interesting group to address questions on floral structure and evolution due to a wide variation in reproductive traits. This review covers a detailed overview of gynoecium features, as well as a new structural study based on Trichilia pallens (Meliaceae), to provide characters to support systematic relationships and to recognize patterns of variations in gynoecium features in Sapindales. Several unique and shared characteristics are identified. Anacrostylous and basistylous carpels may have evolved multiple times in Sapindales, while ventrally bulging carpels are found in pseudomonomerous Anacardiaceae. Different from previous studies, similar gynoecium features, including degree of syncarpy, ontogenetic patterns, and PTTT structure, favors a closer phylogenetic proximity between Rutaceae and Simaroubaceae, or Rutaceae and Meliaceae. An apomorphic tendency for the order is that the floral apex is integrated in the syncarpous or apocarpous gynoecium, but with different length and shape among families. Nitrariaceae shares similar stigmatic features and PTTT structure with many Sapindaceae. As the current position of both families in Sapindales is uncertain, floral features should be investigated more extensively in future studies. Two different types of gynophore were identified in the order: either derived from intercalary growth below the gynoecium as a floral internode, or by extension of the base of the ovary locules as part of the gySapindales is a monophyletic order within the malvid clade of rosids. It represents an interesting group to address questions on floral structure and evolution due to a wide variation in reproductive traits. This review covers a detailed overview of gynoecium features, as well as a new structural study based on Trichilia pallens (Meliaceae), to provide characters to support systematic relationships and to recognize patterns of variations in gynoecium features in Sapindales. Several unique and shared characteristics are identified. Anacrostylous and basistylous carpels may have evolved multiple times in Sapindales, while ventrally bulging carpels are found in pseudomonomerous Anacardiaceae. Different from previous studies, similar gynoecium features, including degree of syncarpy, ontogenetic patterns, and PTTT structure, favors a closer phylogenetic proximity between Rutaceae and Simaroubaceae, or Rutaceae and Meliaceae. An apomorphic tendency for the order is that the floral apex is integrated in the syncarpous or apocarpous gynoecium, but with different length and shape among families. Nitrariaceae shares similar stigmatic features and PTTT structure with many Sapindaceae. As the current position of both families in Sapindales is uncertain, floral features should be investigated more extensively in future studies. Two different types of gynophore were identified in the order: either derived from intercalary growth below the gynoecium as a floral internode, or by extension of the base of the ovary locules as part of the gynoecium. Sapindales share a combination of gynoecial characters but variation is mostly caused by different degrees of development of the synascidiate part relative to the symplicate part of carpels, or the latter part is absent. Postgenital fusion of the upper part of the styles leads to a common stigma, while stylar lobes may be separate. Due to a wide variation in these features, a new terminology regarding fusion is proposed to describe the gynoecium of the order.noecium. Sapindales share a combination of gynoecial characters but variation is mostly caused by different degrees of development of the synascidiate part relative to the symplicate part of carpels, or the latter part is absent. Postgenital fusion of the upper part of the styles leads to a common stigma, while stylar lobes may be separate. Due to a wide variation in these features, a new terminology regarding fusion is proposed to describe the gynoecium of the order.
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.
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 an integral part of the labellum in Gagnepainia, it remains small and almost aborts at later stages of development in G. 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.
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.
A Goethean morphological approach to the study of two species of Loasa in the Rio Clarillo National Reserve in Chile during the 2018 FLO-RE-S Floral Morphology Course.
Entre el 5 y 12 de octubre del 2018 se llevó a cabo la primera versión del Curso Intensivo de Morfología Floral de la red FLO-RE-S (Bull-Hereñu et al., 2016) en las dependencias de la Reserva Nacional Río Clarillo (CONAF). La ONG Laboratorio Flores (www.laboratorioflores.cl) tuvo a cargo la planificación y ejecución de este evento cuyos preparativos comenzaron en marzo del 2018 con las gestiones organizacionales y logísticas en Chile, así como la de la convocatoria de los docentes del exterior. La nómina del curso incluyó a dieciséis estudiantes graduados y de pregrado de diversas carreras incluyendo a cuatro alumnos extranjeros provenientes de Perú y Colombia. El objetivo de este curso fue entregar una introducción general a la morfología floral y también ejercitar el desarrollo de preguntas de investigación y procedimientos observacionales en terreno. Las disciplinas botánicas clásicas que consideran el estudio del organismo vegetal y en particular, aquéllas que se preocupan de reconocer y analizar la forma, han ido mermando su presencia tanto en el currículo escolar como en la educación superior (Iwamoto y Bull-Hereñu 2018). Es en parte por esta razón que se ha venido produciendo un vacío de conocimientos tanto del contenido disciplinar respectivo, así como de las posibilidades y estrategias de investigación que se encuentran en este campo de la biología.
The first FLO-RE-S floral morphology course in Chile.
Monocots are remarkably homogeneous in sharing a common trimerous pentacyclic floral Bauplan. A major factor affecting monocot evolution is the unique origin of the clade from basal angiosperms. The origin of the floral Bauplan of monocots remains controversial, as no immediate sister groups with similar structure can be identified among basal angiosperms, and there are several possibilities for an ancestral floral structure, including more complex flowers with higher stamen and carpel numbers, or strongly reduced flowers. Additionally, a stable Bauplan is only established beyond the divergence of Alismatales. Here, we observed the floral development of five members of the three ‘petaloid’ Alismatales families Butomaceae, Hydrocharitaceae, and Alismataceae. Outer stamen pairs can be recognized in mature flowers of Alismataceae and Butomaceae. Paired stamens always arise independently, and are either shifted opposite the sepals or close to the petals. The position of stamen pairs is related to the early development of the petals. In Butomaceae, the perianth is not differentiated and the development of the inner tepals is not delayed; the larger inner tepals (petals) only permit the initiation of stamens in antesepalous pairs. Alismataceae has delayed petals and the stamens are shifted close to the petals, leading to an association of stamen pairs with petals in so-called stamen–petal complexes. In the studied Hydrocharitaceae species, which have the monocot floral Bauplan, paired stamens are replaced by larger single stamens and the petals are not delayed. These results indicate that the origin of the floral Bauplan, at least in petaloid Alismatales, is closely linked to the position of stamen pairs and the rate of petal development. Although the petaloid Alismatales are not immediately at the base of monocot divergence, the floral evolution inferred from the results should be a key to elucidate the origin of the floral Bauplan of monocots.
The caption of Figure 5 was published incorrectly in the original publication of the article.
Floral development is an important discipline within plant morphology, which in turn is the oldest botanical discipline. Recent achievements in molecular phylogeny, physiology and ecology have recalled the importance of floral development. To evaluate its contemporary relevance, we organized the JPR (Journal of Plant Research) symposium about the floral development. This symposium was co-organized by the Japanese Society of Plant Morphology and Fundación Flores (Chile).
Flower morphology results from the interaction of an established genetic program, the influence of external forces induced by pollination systems, and physical forces acting before, during and after initiation. Floral ontogeny, as the process of development from a meristem to a fully developed flower, can be approached either from a historical perspective, as a "recapitulation of the phylogeny" mainly explained as a process of genetic mutations through time, or from a physico-dynamic perspective, where time, spatial pressures, and growth processes are determining factors in creating the floral morphospace. The first (historical) perspective clarifies how flower morphology is the result of development over time, where evolutionary changes are only possible using building blocks that are available at a certain stage in the developmental history. Flowers are regulated by genetically determined constraints and development clarifies specific transitions between different floral morphs. These constraints are the result of inherent mutations or are induced by the interaction of flowers with pollinators. The second (physico-dynamic) perspective explains how changes in the physical environment of apical meristems create shifts in ontogeny and this is reflected in the morphospace of flowers. Changes in morphology are mainly induced by shifts in space, caused by the time of initiation (heterochrony), pressure of organs, and alterations of the size of the floral meristem, and these operate independently or in parallel with genetic factors. A number of examples demonstrate this interaction and its importance in the establishment of different floral forms. Both perspectives are complementary and should be considered in the understanding of factors regulating floral development. It is suggested that floral evolution is the result of alternating bursts of physical constraints and genetic stabilization processes following each other in succession. Future research needs to combine these different perspectives in understanding the evolution of floral systems and their diversification.
We present a comparative flower ontogenetic study in five species of the genus Eucryphia with the aim of testing whether differences in the organ number observed can be explained by changes in the meristematic size of floral meristem and floral organs. Species native to Oceania, viz. E. milliganii, E. lucida and E. moorei, have the smallest gynoecia with ca. 6 carpels, while the Chilean E. glutinosa and E. cordifolia present more than ten carpels. E. milliganii has the smallest flower with the lowest stamen number (ca. 50), while the other species produce around 200 stamens and more. Standardized measurements of meristematic sectors were taken in 49 developing flowers that were classified into three well-defined ontogenetic stages. Sizes of meristems varied significantly among species within each developmental stage as revealed by ANOVA analyses. Significant regressions between organ number and corresponding meristem size were consistent with the premise that a larger meristem size prior to organ initiation could be determining for a higher organ number. Flower organogenesis in Eucryphia also involves relevant meristem expansion while the organs are initiated, which results in a particular androecium patterning with a chaotic stamen arrangement. Meristem expansion also appears to be slower but more extensive in species with larger initial meristematic size, suggesting that flower phenotype can be determined in ontogeny by this heterochronic interplay of space and time.
Background and aims: Obdiplostemony has long been a controversial condition as it diverges from diplostemony found among most core eudicot orders by the more external insertion of the alternisepalous stamens. In this paper we review the definition and occurrence of obdiplostemony, and analyse how the condition has impacted on floral diversification and species evolution. Key results: Obdiplostemony represents an amalgamation of at least five different floral developmental pathways, all of them leading to the external positioning of the alternisepalous stamen whorl within a two-whorled androecium. In secondary obdiplostemony the antesepalous stamens arise before the alternisepalous stamens. The position of alternisepalous stamens at maturity is more external due to subtle shifts of stamens linked to a weakening of the alternisepalous sector including stamen and petal (type I), alternisepalous stamens arisingde factoexternally of antesepalous stamens (type II) or alternisepalous stamens shifting outside due to the sterilization of antesepalous stamens (type III: Sapotaceae). In primary obdiplostemony the alternisepalous stamens arise before the antesepalous stamens and are more externally from initiation. The antesepalous stamen whorl is staminodial and shows a tendency for loss (type I), or the petals are missing and the alternisepalous stamens effectively occupy their space (type II). Although obdiplostemony is often related to an isomerous gynoecium, this is not essential. Phylogenetically, both secondary and primary obdiplostemony can be seen as transitional stages from diplostemony to either haplostemony or obhaplostemony. Obdiplostemony is the consequence of shifts in the balance between the two stamen whorls, affecting either the alternisepalous stamens together with the petals, or the antesepalous stamens. Conclusions: We advocate a broad definition of obdiplostemony, to include androecia with incomplete whorls, staminodial whorls, anisomerous gynoecia and an absence of petals. As such, the taxonomic significance of obdiplostemony is transient, although it is a clear illustration of how developmental flexibility is responsible for highly different floral morphs.
This paper is a discussion and elaboration of a paper by Prenner & al. (2010), entitled “Floral formulae updated for routine inclusion in formal taxonomic descriptions”. The aim of the Prenner paper was to promote the use of floral formulae in botany and to reach a consensus among botanists for best practice. An important purpose of floral formulae is to induce users to observe and describe flowers accurately. It is proposed that additional information on anther, ovule, style and stigma should be included. Also, only visible organs should be included in a formula and theoretical speculations should be illustrated with floral diagrams, which are complementary to formulae, unless there is good reason to include absent organs. We propose a universal, standardized method to accurately shorthand a description of a flower. The level of detail given in the formula can be highly flexible and depends on the intentions of the user.