Coryanthes, commonly known as Bucket Orchids, is a genus of tropical epiphytic orchids. This genus is abbreviated as Crths in horticultural trade.
Bucket orchids are an excellent example of coevolution and mutualism, as the orchids have evolved along with orchid bees (the tribe Euglossini of the family Apidae) and both depend on each other for reproduction. One to three flowers are borne on a pendant stem that comes from the base of the pseudobulbs. The flower secretes a fluid (see Coryanthes alborosea
picture) into the flower lip, which is shaped like a bucket. The male
orchid bees (not the females) are attracted to the flower by a strong
scent from aromatic oils, which they store in specialized spongy pouches
inside their swollen hind legs, as they appear to use the scent in
dances in order to attract females. The bees, trying to get the waxy
substance containing the scent, sometimes fall to the fluid-filled
bucket. As they are trying to escape, they find that there are some
small knobs on which they can climb on, while the rest of the lip is
lined with smooth, downward-pointing hairs, upon which their claws
cannot find a grip. The knobs lead to a spout (see the Coryanthes leucocorys picture), but as the bee is trying to escape, the spout constricts. At that same moment, the small packets containing the pollen of the orchid get pressed against the thorax
of the bee. However, the glue on the pollen packets does not set
immediately, so the orchid keeps the bee trapped until the glue has set.
Once the glue has set, the bee is let free and he can now dry his wings
and fly off. His ordeal may have taken as long as forty-five minutes.
Hopefully, the bee will go to another flower, where, if the flower is to
be successful at reproducing, the bee falls once again into the bucket
of the same species. This time the pollen packets get stuck to the stigma as the bee is escaping, and after a while the orchid will produce a seed pod.
The bee, having stored the aromatic oils in his back legs, can then fly off to mate with a female bee.