Premise of the Study
This study details the unusual synorganization of the staminate flower in wind‐pollinated urticalean rosids to add the missing pieces that complete the puzzle of the explosive ...mechanism of pollen release in this group.
Methods
Flower buds and flowers were analyzed using light and scanning electron microscopy.
Key Results
The pistillode, stamens, and sepals form a floral apparatus that explosively releases pollen to be carried by the wind. The anthers dehisce when the stamens are still inflexed on the floral bud and are enveloped by the sepals and supported by an inflated pistillode. The distension of the filaments presses the pistillode, which decreases the pressure exerted on the anthers by releasing the air accumulated internally through its apical orifice. The extended filaments and the dehiscent free anthers move rapidly outward from the center of the flower. This movement of the filaments is then blocked by the robust basally united sepals, which causes a rapid inversion of the anther position, thus hurling the pollen grains far from the flower. The pollen grains are released grouped by the mucilage produced in high quantity in the cells found in all floral organs.
Conclusions
The anatomical structure of the pistillode and the finding of mucilaginous cells are the main features that help in the understanding the explosive mechanism of pollen release in urticalean rosids. The pistillode can be considered an exaptation because it was evolved later to provide a new role in the plant, optimizing male fitness.
The syconium is the urn-shaped inflorescence shared by all species of the genus
Ficus
. The orifice at the apex of the syconium is called the ostiole, and it is covered by interlocking bracts. The ...ostiolar bracts can have different arrangements, which only allow the entry of mutualist wasps and promote reproductive isolation among
Ficus
species. Here, we analyze the ostiolar structures that could play a role as selective filter and therefore impact the fig-fig wasp mutualism in the neotropical
Ficus
sections
Americanae
and
Pharmacosycea
. Samples of syconia with pistillate flowers during the receptive phase of seven species of
Ficus
were examined using light and scanning electron microscopy. Tests for histolocalization of substances were employed to detect secretory activity throughout the ostiolar tissues. Our results indicated that the ostiole has two components: ostiolar bracts and the periostiolar zone. Interspecies variation in ostiolar bract arrangement in both sections studied was broader than previously reported. We report for the first time for
Ficus
: (i) two types of ostiolar osmophores (mesophyll and diffuse), that could be a source of volatile compounds for attracting fig wasps; (ii) colleters in the axil of ostiolar bracts, which probably lubricate and facilitate the entry of pollinating wasps into the syconial cavity; (iii) secretory trichomes around the ostiolar bracts, and (iv) syconium basal bracts (
F
.
isophlebia
) covering the ostiole, which are the first physical barrier that the fig wasps must overcome to access receptive pistillate flowers. We describe the zones that compose the ostiole, which support the hypothesis that the ostiole is a selective filter in the interactions of fig trees with Agaonidae fig wasps. We also suggest that ostiolar osmophores, colleters, the periostiolar zone, and the arrangements of the ostiolar bracts may be informative with respect to
Ficus
systematics.
Premise
Celtis is the most species‐rich genus of Cannabaceae, an economically important family. Celtis species have been described as wind‐pollinated and andromonoecious. However, the andromonoecy of ...Celtis has been debated because there are reports of monoclinous flowers with non‐opening anthers on short filaments. Our objective was to study the floral morphogenesis of Celtis to establish the breeding system and to better understand the developmental patterns that lead to the formation of reduced flowers in the genus.
Methods
Flowers and floral buds of Celtis species were studied using scanning electron microscopy, high‐resolution x‐ray computed tomography, and light microscopy.
Results
All flowers initiate stamens and carpels during early floral development, but either stamens or carpels abort during later stages. Thus, at anthesis, flowers are either functionally pistillate or functionally staminate. In pistillate flowers, stamens abort late and become staminodes with normal‐looking anthers. These anthers have no functional endothecium and, in most of the species studied, produce no viable pollen grains. The gynoecium is pseudomonomerous, and its vascularization is similar in the sampled species. In staminate flowers, the gynoecium aborts early resulting in small pistillodes. No vestiges of petals were found.
Conclusions
The species studied are monoecious and not andromonoecious as described earlier. The absence of petals, the carpel and stamen abortion, and the pseudomonomerous gynoecium result in the reduced flowers of Celtis species. The use of high‐resolution x‐ray computed tomography was essential for a more accurate interpretation of ovary vascularization, confirming the pseudomonomerous structure of the gynoecium.
In this study, we reassessed the morphology and distribution of laticifers present in the inflorescences of nine Moraceae and three Urticaceae species and compared the substances found in their ...latices. Reproductive meristems and inflorescences at different developmental stages were collected, fixed and processed for light microscopy analysis. In Moraceae, laticifers occur in almost all inflorescence organs. In Urticaceae, the presence of laticifers in the inflorescence axis and sepals is a novelty, since the family is characterized by having laticifers only in the bark. The laticifers of Moraceae and Urticaceae show a thin pectocellulosic cell wall and are articulated and branched, although they are currently classified as non-articulated branched in Moraceae and non-articulated unbranched in Urticaceae. The latex contains proteins and alkaloids. Lipids are common in Moraceae latex, whereas phenolic compounds occur in the Urticaceae latex. Polysaccharides occur in the majority of the species studied, an unprecedented finding for the group. Thus, we found that the non-articulated type of laticifer may not consist of a synapomorphy for Moraceae and Urticaceae. Moreover, the laticifer branching in the inflorescences of Urticaceae indicates that its distribution and ramification as acknowledged in the literature (restricted to the bark and unbranched) should be reevaluated and may not constitute synapomorphies for this family either. The adaptive value of laticifers for Moraceae and Urticaceae is high, since they occur widely in the plant body of their representatives. The presence of proteins and alkaloids in the latex and the absence of starch grains are probably conserved traits in the urticinean rosids.
PREMISE OF THE STUDY:
Pentaclethra and Dimorphandra (Leguminosae) have long been considered a possible enigmatic link between caesalpinioids and mimosoids because they both have an imbricate calyx ...and heteromorphic androecium, floral features that are rare among mimosoids but common among caesalpinioids. This study compared the developing flowers of Dimorphandra mollis and Pentaclethra macroloba to determine whether the shared floral conditions also have the same ontogenetic origin.
METHODS:
Buds of different sizes and flowers were processed for surface (scanning electron microscopy) and histological (light microscopy) examination.
KEY RESULTS:
The floral meristem initiates five sepal primordia in a modified helical order in both species. The median sagittal sepal is adaxial. The overlap of the sepals during elongation culminates with the formation of the imbricate calyx. Heteromorphic androecia arise in the intermediate stages of development. In P. macroloba, the fertile pollen‐bearing stamens are antesepalous, robust and short, and the anthers carry a robust apical gland; the staminodes are long and white with a vestigial apical gland. In contrast, in D. mollis the fertile pollen‐bearing stamens are antepetalous without glands and as long as the staminodes. The staminodes are thinner with an expanded apical region.
CONCLUSIONS:
The imbricate calyx and the heteromorphic androecium in the studied species originated via distinct pathways, favoring the hypothesis of homoplasy of these conditions. The pathways observed in P. macroloba are more similar to those observed in caesalpinioids than to those observed in mimosoids, indicating that although the floral development differs between the species studied, it supports the basal placement of Pentaclethra among mimosoids.
Abstract
Most species of Urticaceae, the nettle family, have small and inconspicuous, diclinous flowers, in which the perianth, androecium and gynoecium tend to vary in number. Our objective was to ...study the morphology of the developing flowers of seven species of Urticaceae to understand the pathways that lead to the different patterns of floral reduction and the complex development of pseudomonomerous gynoecia. Buds and flowers were prepared for electron and light microscopy. Vascularization was studied via high resolution X-ray computed tomography micro-CT. Only one whorl of perianth organs is initiated, except for Phenax sonneratii, the flower of which is achlamydeous; variation in perianth merosity results from absence of organs from inception; dicliny results from the absence of stamens from inception (pistillate flowers) and from pistil abortion at intermediate developmental stages (staminate flowers). The gynoecium results from a primordium that divides partially forming two congenitally united primordia (most species) or from a single primordium that apparently does not divide. The gynoecium is served by a single (four species), or two vascular bundles. This second condition is expected for a pseudomonomerous gynoecium. Pistillode or rudimentary carpels occur in staminate flowers. The comparison among species shows that the developmental processes acting in the floral construction in Urticaceae is diverse.
Abstract Species of Cannabaceae are wind pollinated, have inconspicuous and reduced flowers that are pistillate, staminate and apparently perfect on the same individual or on different individuals, ...with a single-whorled perianth and a pseudomonomerous gynoecium. Our objective is to understand the developmental processes that lead to such a reduced flower morphology and polygamy in Cannabis sativa, Celtis iguanaea and Trema micrantha. Floral buds and flowers were processed for surface, histological examinations and 3D reconstructions of vasculature. The single-whorled perianth is interpreted as a calyx because the organs are robust, have a broad base, an acute apex and quincuncial aestivation and are opposite the stamens. Petals are absent from inception. The dicliny is established at different development stages: stamens or carpels are absent from inception (Cannabis sativa), initiated and aborted during early (Trema micrantha, before sporo/gametogenesis) or late (Celtis iguanaea, after sporo/gametogenesis) development. Furthermore, in all species studied the carpels are congenitally united and the pseudomonomerous nature of the gynoecium is confirmed. Glandular trichomes are distributed on the bracts, sepals, anther connective and receptacle. Special floral features shared by species of Cannabaceae include precocious ovule development and sepals that are each vascularized by one bundle. The reduced flowers of Cannabaceae are the result of the absence from inception and/or abortion of organs and even of a whole whorl at different developmental stages, which were probably selected in response to pressures exerted by the similar pollination mechanism.
Small flowers with tubular calyces and connate stamens, a small number of whorls and organs per whorl are found in species of the tribe Cecropieae (Urticaceae). This study elucidates the processes ...that lead to such floral conditions by comparing the morphology of the developing flowers of
Cecropia pachystachya
,
Coussapoa microcarpa
and
Pourouma cecropiifolia.
Buds and flowers were examined under scanning electron and light microscopy. The tubular calyx originates from the activity of a peripheral annular meristem that results in a tube with two or three lobes. In the staminate floral meristem, the androecium primordium arises as a central bulge that elongates and originates two stamens with the filaments basally or totally united; the anthers can also be united. In the pistillate floral meristem, the gynoecium primordium also arises as a central bulge that elongates and originates two carpel primordia: one expands, forming a cleft and an ovule, and the other does not differentiate and remains rudimentary. Pistillate and staminate flowers result from the absence of the stamen or carpel, respectively, from inception. Petals are also absent from inception. The formation of the tubular calyx and connate stamens occurs very early in development, characterizing a congenital union. The union of anthers by the connectives in
C. microcarpa
is postgenital and occurs between epidermal cell walls through a weak cohesion. The floral development of Cecropieae is quite similar and less labile than in the other Urticaceae species.
Premise of research. Ampelocera glabra is an andromonoecious, wind-pollinated species of Ulmaceae, the elm family. This family comprises two clades: tropical and temperate. The species that have been ...morphologically studied so far all belong to the temperate clade. Ampelocera glabra is included in the tropical clade and is remarkable due to its atypical flower merism when compared to other Ulmaceae and to most other rosids: tetramerous calyx, polyandrous androecium, and pseudomonomerous gynoecium. Thus, our objective was to study the ontogeny and vascularization of the A. glabra flower to elucidate the processes involved in the atypical merism and in the reduced structure of the whorls. Additionally, the mating system of A. glabra was checked and its floral structure was associated with anemophily, thus contributing to reproductive studies of this species under threat of extinction.
Methodology. Flowers and early to late floral buds were processed for surface (SEM) and histological (LM) investigations and 3D reconstructions (X-ray microcomputed tomography).
Pivotal results. Ampelocera glabra is actually a monoecious species with functionally staminate and functionally pistillate flowers, containing carpellodes and staminodes, respectively. The single perianth whorl is composed of sepals, and there is no hypanthium. Each primordium of the sepals and stamens arises individually. A central common primordium gives rise to two carpels, but only one houses an ovule. Each carpel is vascularized by one dorsal bundle, and the carpel that bears the ovule is also vascularized by one ventral bundle. Thus, the gynoecium displays a reduction in the vascular bundle in the nonovulate carpel.
Conclusions. The differences in merism between the calyx and the androecium are explained by the space that can support the increase in organ number. The increase in stamen number and the reduced gynoecium (pseudomonomerous) enable a high pollen∶ovule ratio, which is an important condition for any anemophilous species.
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