Pollination specialization is promoted by floral features that favor pollinator fidelity and hinder the access to resources by other visitors. We investigated the pollination mechanism of one understory herb in southeastern Brazil. Calathea cylindrica flowers year-round and its flowers are peculiar because of the fusion and modification of some elements, asymmetry, secondary pollen presentation, hidden nectar, and a long and narrow tube, which is closed before pollinator visit. Pollination occurs by means of an explosive mechanism, and once it is triggered, the floral parts do not return to their initial position. Thus, there is only a single possibility for pollen transference. Pollinators are female Euglossini bees and all flowers have already been visited by mid-morning. Specific movements with enough force are necessary for the visitors to access the nectar. Bagged flowers secreted around 13 µL of nectar with 32% of sugar concentration. Nectar secretion continues after removals, but in small volumes. Continual flowering, high production of nectar and secretion after pollination may promote pollinator fidelity. The complex floral structure, the secretion in which the flower base (nectar chamber) is dipped, and the narrow tube with inner hairs make the access to nectar difficult and may work as barriers for other visitors. Altogether, these factors seem to regulate the highly specialized pollination system of Calathea cylindrica.
bee; Euglossini; floral specialization; nectar; pollination
