A story of ants, bees and orchids: the Bucket Orchids
The genus Coryanthes (Asparagales - Orchidaceae) has one of the most complex flowers structures of the highly diverse orchid family. Sepals and tepals are usually turned back and soon wither after anthesis (the period during which a flower is fully open and functional).
The fleshy lip of the Coryanthes flower is composed of three parts: the cup shaped hypochil (the lower part of the lip), the partially covered, tubular mesochil (the intermediate or middle part of the lip), and the bucket-like enlarged epichil (the terminal part of the lip), which is filled up to the “exit” with a fluid, secreted by two broadly-falcate protuberances, called pleuridia, at the base of the column.
Coryanthes species grow on trees, and exclusively in ant nests of the genera Azteca, Campanotus, and Crematogaster, in so-called “ant-gardens”. These arboreal communities can reach diameters of 150 cm with the ant nest comprising 80 cm. Both organisms share a destiny because the plant is condemned to death if the associated ant colony dies. The plants offer nectar in extrafloral nectaries and provide a framework for nest construction with their root system, while the ants defend the plants against herbivores and additionally fertilize them with vertebrate feces. This abundant provision of nutrients by the ants allows the plants to grow rapidly.
All Coryanthes species are pollinated by males bees of the genera Euglossa, Eulaema, and Euplusia. The bees are attracted by the odor of the flowers and swarm around them. They land on the hypochil of the flower and try to get below the hood to seek the fragrance compound. In trying to obtain a footing on the waxy, smooth mesochil they loose their footing and fall in the bucket-like epic hill which is filled with a mucilaginous fluid, where their wings are moistened. The only way to escape is crawling out through a tunnel, formed by the epichil of the lip and the column. The pollinator touches first the stigma and afterwards the sticky viscidium, which glues the whole pollen mass (pollinium) on him. After a second “error”, the flower is pollinated.
These photos show the species Coryanthes speciosa and the Orchid Bees, Euglossa tridentata (Apidae - Euglossini) on Coryanthes speciosa.
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Photo credit: [Top: ©Eerika Schulz | Locality: Royal Gardens, Hannover, Lower Saxony, Germany, 2013] - [Bottom: ©Ian Morton | Locality: Hickatee Cottages, Punta Gorda, Toledo District, Belize, 2002]