Pterandra pyroidea: a case of pollination shift within neotropical Malpighiaceae

Comparative analysis of the processes involved in the loss of elaiophores in two species of the christianelloid clade (Malpighiaceae)

Alicia anisopetala and Callaeum psilophyllum are two closely related species that belong to the christianelloid clade of the family Malpighiaceae. Both species are pollinated by oil-collecting bees and exhibit variations at specimen and population level in the number of elaiophores per flower. These floral glands that secrete non-volatile oils constitute an ancestral trait for the family. There is evidence that the observed variations in the number of elaiophores can be the result of processes of connation or reduction associated with differences in their vascularization. In order to identify which process occurs in each species, we conducted an anatomical study in natural populations of both species distributed along a wide range of their geographical distributions in Argentina. We collected flowers of different individuals, counted the number of elaiophores per flower, carried out exomorphological observations, and used conventional histological techniques to examine the vascularization of these glands. The floral anatomy of both species does not show any modifications in other whorls related to the fusion or reduction of elaiophores. Our results indicate that the process of loss of elaiophores in A. anisopetala is caused by incomplete connation and in C. psilophyllum by reduction, suggesting that the processes that lead to the loss of elaiophores in Malpighiaceae are homoplastic and would not reflect phylogenetic signals.

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

The flowers of the species of Malpighiaceae in the Neotropical Region are relatively uniform in their morphology due to their dependence on oil-collecting bees as their main pollinators. However, many species of the genus Galphimia seem to have acquired a different floral syndrome, lacking markedly zygomorphic flowers and developed elaiophores in the calyx. Likewise, these species present anthers with great development, probably in response to the selection of pollinators that collect pollen. Galphimia australis incorporated some of these traits but also retained some residual characteristics typical of species pollinated by oil bees. This leads to many questions on how these flowers ensure their pollination. Inquiring about the reduction or modification of these characteristics allows us to understand how G. australis achieves a different pollination syndrome. In this research, we carry out a detailed morphological and anatomical study of the flowers and pollen grain devolvement of G. australis and floral visitors were observed and captured. Results were analyzed in order to determine how this species changed from the oil-floral syndrome, typical of neotropical Malpighiaceae, to one syndrome with pollen as the main reward.

Structural diversity of elaiophores in Argentine species of Malpighiaceae: morphology, anatomy, and interaction with pollinators

Most Neotropical Malpighiaceae species are characterized by having zygomorphic flowers and oil glands in the sepals called elaiophores; these floral characteristics are associated with a particular pollination syndrome through oil-collecting bees. This work proposes a study about the structural characteristics of elaiophores in 18 species of Malpighiaceae present in Argentina. The main objectives are to describe the morphology and anatomy of the elaiophores, to detect variation in the number of glands, to compare similarities or differences in elaiophores of species belonging to different lineages, and to know about the potential pollinators and their association with the structural traits of the elaiophores. The morphology and the anatomy were studied using traditional methods of scanning electron and bright-field microscopes. Field trips were carried out to capture oil-collecting bee species on flowers, in different natural populations. Different measurements were taken in the flowers, elaiophores, and oil-collecting bees and were statistically analyzed. Although elaiophores showed a common pattern, some particularities in number, morphology, and anatomy were detected; few of these seem to be restricted to some groups of species phylogenetically related. As regards pollinators, a positive tendency was observed between the size of the flowers, elaiophores, and oil-collecting bees. However, the thickness of the cuticle presented a negative association with the size of the elaiophore and consequently with the floral diameter, which could be presumably related to the foraging behavior and/or the structure of oil-collecting apparatus of the bee species.

Pterandric Acid – its Isolation, Synthesis and Stereochemistry

Some plant families have a specialized type of pollination system, with floral lipid rewards for pollinators, which is common. In neotropical Malpighiaceae species like Pterandra pyroidea, this specialized type of pollination system is apparently shifting from floral oils/lipids to pollen reward. Mass spectrometric analysis (GC/MS-EI) indicated that P. pyroidea floral oil has a unique chemical composition, i.e., few fatty acid constituents possessing acetoxy groups at positions 5 and 7, which is distinct from the other floral oils of sympatric Malpighiaceae species. The structure of the major floral oil constituent, a novel fatty acid, a nti-5,7-diacetoxydocosanoic acid, was confirmed based on synthesis, mass fragmentation, and 1H and 13C NMR analyses; the compound is herein named pterandric acid.