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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. [ABSTRACT FROM AUTHOR]

Premise of research. The flower of Leandra melastomoides (Melastomataceae) exhibits a singular condition that is the presence of two distinct and opposite portions in the sepals forming what is known as a double calyx. These portions may correspond to individual sepals, explaining the recognition of two calyx whorls. No studies resolving this structure are available in the literature. Thus, we aimed to elucidate the nature of the double calyx of L. melastomoides by analyzing its ontogeny. This approach allowed us to test hypotheses about how this structure developed. Methodology. Flowers and buds were preserved and prepared for observation in LM and SEM. Pivotal results. The sepals originate in the margin of the floral apex as six spherical primordia in a single outer whorl. The growth is unidirectional until a basal protuberance arises on the ventral surface of each primordium, which allows us to distinguish an upper and a lower part of this structure. The upper portion later takes on a dorsal position. The lower portion shows laminar growth, various vascular traces, and nonglandular emergences. The dorsal portion becomes conical, is lined with nonglandular emergences, and is supplied by a single vascular trace. The vascularization of each part of a sepal has a common origin from the radial divergence of the same trace that emerges from the vascular ring of the hypanthium. Conclusions. The calyx of L. melastomoides actually consists of only one whorl, because both dorsal and laminar parts of a sepal originate from a single primordiumin a peripheral region of the floral meristem. The dorsal projection is similar to that described in the literature under the term Vorläuferspitze. The understanding of the existence of two distinct ontogenetic modules for the same organ allows us to compare it with other organs and taxonomic groups and to search for a better descriptive terminology for the structure in this group. [ABSTRACT FROM AUTHOR]

Premise of research. We present a detailed analysis of the floral ontogeny ofAmburana cearensis, which is an early-branching papilionoid legume with an unusual floral morphology. Especially the reduced one-petalled corolla is noteworthy and stimulates the question about the ontogenetic background of this reduction. Are all five petals initiated and later reduced, or are four petals completely lost (i.e., without any primordia evident)? Ontogenetic studies of early-branching papilionoids provide important insights for the understanding of relationships down to caesalpinioid legumes and up to derived papilionoid lineages. Methodology. We analyzed inflorescences, flowers, and flower buds with the SEM using standard procedures. Pivotal results. Sepals and petals are initiated bidirectionally, which is a rare character among papilionoid legumes. The reduced one-petalled corolla is the result of early suppression of four petal primordia. Stamen formation is in reversed unidirectional order starting from the adaxial side of the flower. This is a rare character among Leguminosae. Floral characters that could be important for floral ecology are the rapid growth of the adaxial petal, which participates in bud protection; a long hypanthium with nectariferous stomata in the lower half; two fenestrae at the left and right of the adaxial stamen, through which nectar is accessible; and reduced anthers in the inner stamen whorl (i.e., heteranthery), which might be related to the reduction of four petals. Conclusions. Our study highlights the importance of ontogenetic studies among the diverse early-branching papilionoid lineages. Floral ontogeny in Amburana deviates considerably from the unidirectional pathway that is a common pattern among more derived papilionoid lineages. Organ reduction is based on the abortion of initiated primordia. Our study contributes to a better understanding of early-branching papilionoids and their systematic relationships. [ABSTRACT FROM AUTHOR]