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.