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Background: Intraspecific variations in floral traits of species over its geographic range can be associated with differences in pollinator assemblages and/or with environmental conditions. Aims: We evaluated the area of elaiophores in different populations of Stigmaphyllon bonariense (n = 9) and S. jatrophifolium (n = 6), and we hypothesised a marked reduction in their size towards their southern limits of distribution, associated with different oil-collecting bee assemblages. Methods: Area of elaiophores was calculated and we carried out linear correlations with floral size, pollinators, visitation rate and pollinator size along the latitudinal gradient of the plants' distributions. Moreover, we examined the relative size relationships using allometric analyses, to verify this reduction. Results: Floral elaiophore area decreased with latitude. However, for S. bonariense we observed an allometric reduction in elaiophore area with respect to floral size, while for S. jatrophifolium an isometric reduction was found. In both species, pollinator richness and visitation rate did not diminish with latitude, but pollinator size for S. bonariense varied. Conclusions: Our results show a reduction in the size of elaiophores in both species along their distribution range, with dissimilar tendencies, suggesting that these species may have different selection pressures that cause variation of their phenotypic traits.

Anther and gynoecium structure and embryological information in Koelreuteria and Sapindaceae as a whole remain understudied, as well as the evolution of imperfect flowers in the latter. The aims of this study were to analys in K. elegans subsp. formosana the anther and gynoecium structure and the development of male and female gametophytes in the two floral morphs of putatively imperfect flowers. Standard techniques were applied for LM and SEM. Compared to the normal anther development in staminate flowers, a delayed programmed cell death of tapetum, septum and middle layers on the onset of microspore stage result in indehiscent anthers in the functionally pistillate flowers. Orbicules are reported for the first time in Sapindaceae. Gynoecium development in functionally pistillate flowers is normal, whereas in functionally staminate ones a pistillode with degenerated ovules at the tetrad stage is formed. The pollen tube transmitting tract consists of one layer of epithelial cells with a small lumen in the style and ovary. The anatomy of the latter revealed an axile placentation and complete septum. Reproductive characters of Koelreuteria shared with other Sapindaceae taxa are a secretory binucleate tapetum, simultaneous cytokinesis, unicellular stigmatic papillae, Polygonum type megagametophyte with ephemeral antipodals, and ovules campylotropous, with funicular obturator and amphistomic micropyle. Imperfect flowers in the family are triggered by defective sporophytic tissues impacting on the normal development of microspores and megaspores, disrupting embryological events in staminate and pistillate organs at different developmental stages. Reconstructing ancestral character state under parsimony revealed that two ovules per locule, absence of obturator, presence of hypostase, and binucleate tapetum may be regarded as plesiomorphic for Sapindaceae. These analyses have provided information on the evolution of embryological characters in the family and its phylogenetic significance.

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