Apomixis and adventitious polyembryony have been reported for several species of Bombacoideae, including Eriotheca pubescens, a tree species of the Neotropical savanna (Cerrado) areas in Brazil. However, the origin of polyembryonic seeds and their importance for the reproduction of the species remained to be shown. Here, we analyzed the early embryology of this species to establish the apomictic origin of extranumerary embryos. We also observed the geographic distribution of polyembryony in E. pubescens, and tested if apomixis was related to the source of pollen (self or cross) and population density. Moreover, we tested if polyembryonic apomictic embryos would develop normally into seedlings. In the observed seed primordia, after a relatively long quiescent period, the zygote developed into a sexual embryo concurrently with adventitious apomictic embryos which developed from nucellus cells. Adventitious embryos develop faster than sexual ones and are morphologically similar, so that 44 days after anthesis it was virtually impossible to distinguish and trace the fate of the sexual embryo. Polyembryony is widely distributed in populations some 400 km distant, and only one strictly monoembryonic individual was observed during the study. The number of embryos per seed varied between fruits and individuals but was significantly higher in seeds from cross-pollinations than from selfs, although fruit and seed set after crosses were much lower than after selfs. Embryo development into seedlings depended on their weight at germination, but polyembryonic seeds germinated and produced up to seven seedlings per seed in greenhouse conditions. Adventitious embryony and apomictic seedlings would explain the mostly clonal populations suggested by molecular studies.

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The ability of plants to generate fertile offspring is influenced by morpho-physiological and ecological factors. Hence, reproductive success is directly linked to factors affecting quantity and quality of their progeny. In the Cerrado (savanna) of Brazil, the Vochysiaceae is a widely distributed and ecologically important family. Factors affecting pre-dispersal seed predation and abortion were studied for populations of Callisthene fasciculata, C. major, Qualea multiflora and Q. parviflora. To characterize differences between genera, as well as among species, study areas, and individuals, we quantified pre-dispersal seed predation and abortion. Differences of seed abortion among the species were related to intrinsic reproductive features and not to area or other factors. In contrast, seed predation varied not only among species but also among areas and among individuals. Only C. fasciculata showed no seed predation. In Qualea species, insect predators were found inside the seeds; whereas predators of Callisthene species were outside seeds. In both genera, seed abortion correlated negatively with area size, as did pre-dispersal seed predation, which suggest seed abortion may be a counter-measure to avoid predation. Although seed abortion and predation reduced the progenies of the studied species, seed production did not differ from other Cerrado species.

Ageratum has a complex circumscription, and recent studies have indicated its polyphyletism. The genus has been placed in the tribe Eupatorieae whose embryology is not fully known. Embryological data are conservative and important indicators of phylogenetic relationships and can improve family relationships. This study presents, for the first time in Eupatorieae, embryological data for Ageratum conyzoides and A. fastigiatum. Both species have common features of the family such as a unitegmic anatropous ovule, basal placentation, secretory tapetum, Polygonum megagametophyte, and Asterad embryogenesis. The data obtained reinforce the heterogeneity of the family embryology and show, for the first time, the anther wall development of the monocotyledonous type for Asteraceae. The species studied show also differences between themselves. A. conyzoides has bisporangiated and introrse anthers, conspicuous pappus, and cypselae with trichomes on the ribs, whereas A. fastigiatum has tetrasporangiate and latrorse anthers, pappus absent at maturity, and glabrous cypselae. The data presented support recent phylogenetic molecular studies, suggesting the replacement of A. fastigiatum to another genus along with Gyptidinae.