Floral development of the myrmecophytic Acacia cornigera (Leguminosae)

Abstract

Background: The Neotropical ant-acacias show morphological variations in their vegetative characteristics as a consequence of their relationship with ants. However, there is no information regarding whether floral organs have also undergone any modification that prevents resident ants from approaching the inflorescences in anthesis. Questions: Are the patterns of floral development affected by the relationship with ants? Is there any floral organ or structure involved in avoiding the presence of ants during the flowering period? At what stage of development do these modifications arise, if at all? Studied species: Acacia cornigera (L.) Willd. Study site: Santiago Pinotepa Nacional, Oaxaca and Los Tuxtlas, Veracruz. March and May 2015. Methods: Dissections of inflorescences in every developmental stage from two populations, were examined using scanning electron microscopy. Results: The inception patterns of the calyx (irregular), corolla (simultaneous), androecium (acropetally in alternate sectors) and gynoecium (precocious) agree with previous reports for non-myrmecophyic species of the Acacia genus. In mature stages, the presence of stomata is characteristic of bracts and petals. Conclusions: Floral development is not affected by ant-acacia interactions; however, the occurrence of stomata on bracts and petals could be an important feature indicative of secretory structures to resolve the conflict of interest between ants and pollinators during the flowering period. In this sense, a new approach based on histological analyzes will be necessary in flowers of A. cornigera.