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Background and Aims Moraceae, the family of mulberry and fig trees, displays small homogeneous flowers but extremely diverse inflorescences ranging from simple and branched to complex and condensed. Inflorescences also vary in flower organization in the receptacle, in the degree of flower condensation and in receptacle shape. Thus, the objective of the present study was to compare the inflorescence morphogenesis of Moraceae species, to investigate whether clades with a similar pollination mode share the same patterns of inflorescence development and the developmental stages at which we observe the key changes resulting in the diversified inflorescence architecture that culminates in the Ficus syconium. Methods Inflorescences at different developmental stages were sampled from Brosimum gaudichaudii , Castilla elastica , Clarisia ilicifolia , Ficus pertusa , Maclura tinctoria and Morus nigra and processed for surface and anatomical analyses. Key Results The inflorescence morphogenesis of the studied species is highly variable. The shape of the inflorescence meristem (bulging, hemispheric or elongated), the initiation order and arrangement of flowers along the receptacle and the occurrence of bracts vary between related species. This diversity originates early during inflorescence development. Brosimum gaudichaudii , C. elastica and F. pertusa have flowers enclosed or immersed within the receptacle, although inflorescences begin their development as flat and open structures, as occurs in the other three study species. Conclusion Comparison of the inflorescence morphogenesis in Moraceae species allows us to infer that evolutionary ontogenetic changes driven by pollinators culminate in the enclosure of flowers inside the receptacle, as occurs in the Ficus syconium. [ABSTRACT FROM AUTHOR]

Premise of research. Moraceae, the well-known mulberry or fig family, displays small, inconspicuous, diclinous flowers that are very different from many other rosids. One remarkable condition is the gynoecium that is unilocular and uniovulate but composed of two carpels, characterizing a type of pseudomonomery. The pathways that lead to the formation of such a pseudomonomerous gynoecium are insufficiently known. Therefore, the objective of the present study was to elucidate the developmental pathways of this intriguing type of gynoecium in six species representing six of seven tribes recognized in Moraceae: Brosimum gaudichaudii , Castilla elastica , Clarisia ilicifolia , Ficus citrifolia , Maclura tinctoria , and Morus nigra. Methodology. Buds at different stages of development and flowers were processed for surface and anatomical studies. Pivotal results. The gynoecium meristem forms at first a single protuberance in the center of the flower, which then divides, originating two carpels that elongate asymmetrically, but only one initiates an ovule. After elongation of the young carpels, significant differences are found: (1) the two carpels take part in ovary, style, and stigma formation, although only one initiates an ovule in the ovary, and (2) the longer carpel contains an ovule, whereas the smaller carpel is simply a component of the ovary (M. tinctoria). The developed ovary of all species is vascularized by two dorsal traces, attesting to the participation of two carpels. All species except M. tinctoria have two stigmatic branches that, at the time of receptivity, may differ in length. Conclusions. The formation of a pseudomonomerous gynoecium in Moraceae is a condition of carpel dimorphism that manifests itself along an ontogenetic gradient. Such a gradient is evident in the stigma formation, which may involve both carpels, ovulate or not, resulting in symmetrical stigmatic branches or in asymmetrical stigmatic branches, with the shortening or complete absence of one branch. The structure of the pseudomonomerous gynoecium may be the reflection of a balance between the decrease in the number of ovules and the increase and/or maintenance of the equivalent stigmatic surface. [ABSTRACT FROM AUTHOR]