Most species of Neotropical Malpighiaceae are pollinated by oil-collecting bees of diverse sizes, but the effect of pollinator size on their reproductive success has still not been addressed in the literature. We performed a comparative description of stigma arrangements, analyzing the reproductive system and reproductive success and assessing pollinator sizes in Stigmaphyllon bonariense and Stigmaphyllon jatrophifolium. We collected flowers in three natural populations, conducting pollinator censuses and captures and performing manipulative experiments to determine the plants breeding system. We analyzed the morphology of stigmas and their receptivity and calculated the perimeter of the triangle formed by the stigmas (ST). Pollinator sizes, potential area for pollen transfer (PAPT), and the frequency of visits were also calculated. Stigma arrangement resulted in inverted triangles, and the ST was smaller in S. jatrophifolium than in S. bonariense. The overlap between ST and PAPT suggests that pollinators of all sizes were efficient in pollinating S. jatrophifolium, whereas only large and very large pollinators where efficient in S. bonariense. Moreover, very large pollinators had the highest visit frequencies. Our results indicated that both species are obligate xenogamous, pollinator-dependent, and present pollen limitation. We observed an increase in reproductive success related to the marked turnover in pollinator assemblage throughout the flowering season. These findings suggest that fruit and seed sets vary according to the context of the pollinators and that large pollinators would have the best performance.

Stigmas arrangement, reproductive system, and maternal reproductive success in two species of Stigmaphyllon (Malpighiaceae): does pollinator size matter?

Oil flowers of Malpighiaceae and its oil-collecting bees: loyalty and robbery in a highly specialized system

Catasetum fimbriatum is a dioecious species whose flowers fully adapted to an euglossinophilic mode of pollination. Euglossini male bees collect the volatile fragrances which are produced in osmophores on the flowers. In order to understand the mechanism of scent secretion and floral interaction with the pollinator, we describe the location, histochemistry, anatomy, and ultrastructure of osmophores in pistillate and staminate flowers of this species. Fresh flowers were submerged in neutral red solution to locate the position of the osmophores. Other histochemical test performed includes the NADI reaction to detect terpenoids, Sudan IV for lipids, and Lugol’s iodine solution to detect starch. Anatomical and ultrastructural traits were studied with bright field and transmission electron microscopes, respectively. The location of osmophores differs between pistillate and staminate flowers. In pistillate flowers, secretory tissues were observed on the ribbed adaxial surface of the labellum, but not on its margins, whereas in staminate flowers, they were found throughout the adaxial surface of the labellum and especially in the fimbriae. Anatomy and ultrastructure of the osmophores in the labellum of both types of flowers were similar. They present characteristics of metabolically active cells, such as abundant mitochondria, rough endoplasmic reticulum, vesicles, plastids with starch grains, and lipid globules. Granulocrine secretion and cycles of cytoplasmic contraction and expansion appear to allow the release of products without involving the rupture of the cuticle. Individuals of Eufriesea auriceps and Euglossa sp. were captured in staminate and pistillate flowers but, it seems likely, that only the former pollinates this orchid species.

Anatomy and ultrastructure floral osmophores of Catasetum fimbriatum (Orchidaceae).

Are the floral morphology and anatomy of Galphimia australis, an atypical neotropical Malpighiaceae, associated to a new pollination syndrome?

Diversity and functional roles of floral glands in Malpighiaceae: insights in Lophopterys floribunda W.R. Anderson & C. Davis.

Heteranthery has been largely associated with a division of labour between anthers. Most species of Stigmaphyllon (Malpighiaceae) present heteromorphic anthers and glandular connectives of different development; yet, the functional meaning of this condition has never been explored in the genus. The aims of this study were to provide a comparative description of the structure and development of anthers and their connective glands in S. bonariense and S. jatrophifolium and to assess the existence of division of functions. Natural populations were selected to collect flowers at different stages. Anthers were subjected to morpho-anatomical, histochemical and pollen viability studies. For both species, abundance of pollen grains and size of anther and their connective glands were estimated. Three types of stamens are recognized: stamen with small, intermediate and large anthers. Anthers of both species exhibit a similar glandular tissue in the connective, and the histochemical analysis revealed that it produce a mucilagous secretion. The pattern of anther wall development, stainability and release of pollen grains was identical among anther types. For both species, we observed a positive relationship between anther size and abundance of pollen grains, but an inverse relationship between area of anthers and size (area and thickness) of connective glands in small anthers vs. intermediate and large ones. Our results evidence a specialization of anthers related to division of labour between heteromorphic stamens in two species of Stigmaphyllon. Thus, one set of anthers produces large amount of pollen grains for pollination and another sets large quantities of mucilage, which would improve pollen transport (better adherence to pollinator body and dampness maintenance). Nevertheless, heteranthery in both Stigmaphyllon species would represent a transitional state towards the division of labour rather than a stable state.

Structure and development of anthers and connective glands in two species of Stigmaphyllon (Malpighiaceae): are heteromorphic anthers related to division of labour?

Torretta Juan Pablo

Papers

Structure and development of anthers and connective glands in two species of Stigmaphyllon (Malpighiaceae): are heteromorphic anthers related to division of labour?