Coryanthes, commonly known as bucket orchids, is a genus of neotropical epiphytic orchids in the family Orchidaceae (order Asparagales), native to South America, Central America, Mexico, and Trinidad. In horticultural trade the genus is abbreviated "Crths." The genus is best known as a textbook example of coevolution and pollinator mutualism: its flowers are pollinated exclusively by male orchid bees (tribe Euglossini, family Apidae), and both parties depend on the relationship for reproduction.
Each inflorescence bears one to three flowers on a pendant stem arising from the base of the pseudobulb. The flower's lip is modified into a bucket-shaped structure that fills with fluid secreted by two glands; according to naturalist Anthony Huxley, this fluid contains an intoxicating substance. Male bees are drawn to the flower by a strong scent of aromatic oils, which they collect and store in specialized pouches on their swollen hind legs, apparently to use in later courtship displays for females. While gathering the scent, bees often slip and fall into the fluid-filled bucket. The bucket's interior is lined with smooth, downward-pointing hairs that offer no grip, except for a set of small knobs that lead the trapped bee toward a narrow spout. As the bee struggles through the spout, it constricts around the insect, pressing the flower's pollen packets against the bee's thorax; the glue on these packets takes time to set, so the bee remains held — sometimes for as long as 45 minutes — until it can finally fly free. Pollination is completed when the bee, now carrying pollen packets, falls into the bucket of a second Coryanthes flower and the packets are deposited on that flower's stigma during its escape.
Coryanthes flowers are among the largest in the orchid family, with some species reported to reach up to 30 cm (12 in) across and 16 cm (6 in) from top to bottom. Coryanthes bruchmuelleri is generally regarded as the largest species in the genus, its unopened flower buds alone reaching nearly 12 cm long. The genus has a notable place in the history of pollination biology: some of the earliest investigations were published by Crüger in 1865, and Charles Darwin documented observations and experiments on Coryanthes in his book on orchid fertilization by insects. Darwin, however, believed female bees were responsible for pollination; it took almost a century before the role of male euglossine bees in the process was correctly identified, in 1961.
Distribution
Coryanthes is native to South America, Central America, Mexico, and Trinidad, where its species grow as epiphytes.
Ecology
Coryanthes flowers are pollinated exclusively by male orchid bees (tribe Euglossini), which are lured by aromatic oils and become temporarily trapped in the flower's fluid-filled, bucket-shaped lip. Escape is only possible through a narrow spout that presses pollen packets onto the bee's thorax before releasing it — a process that can take up to 45 minutes and represents a well-documented case of coevolved plant–pollinator mutualism.
History
Some of the earliest scientific investigations of Coryanthes were published by Crüger in 1865, and Charles Darwin later described his own observations and experiments on the genus in his book on orchid fertilization by insects. Darwin mistakenly attributed the pollination behavior to female bees; the correct role of male euglossine bees was not established until 1961, nearly a century later.
