Dendrobium christyanum

Description

Dendrobium christyanum is a species of orchid (Orchidaceae) endemic to the Chinese island of Hainan. It produces a volatile organic compound that is unrecorded in other plant species. The flowers of this orchid produce a bee pheromone which attracts its pollinator, Vespa bicolor, a species of hornet. The novel feature, first reported in 2009, is supposed to mimic the distress pheromone of the indigenous Asian honey bee Apis cerana (the same chemical as in the European Apis mellifera, which does not occur naturally on Hainan). The chemical compound, (Z)-11-eicosen-1-ol, can be detected by the hornet and is it is assumed this mimicry deceives the insect into visiting the flower without reward (the flowers offer no nectar). V. bicolor preys on honey bees to feed its larvae. The European beewolf (Philanthus triangulum) is also able to detect this compound when hunting bees. Dendrobium is a genus of mostly epiphytic and lithophytic orchids in the family Orchidaceae. It is a very large genus, containing more than 1,800 species that are found in diverse habitats throughout much of south, east and southeast Asia, including China, Japan, India, the Philippines, Indonesia, Australia, New Guinea, Vietnam and many of the islands of the Pacific. Orchids in this genus have roots that creep over the surface of trees or rocks, rarely having their roots in soil. Up to six leaves develop in a tuft at the tip of a shoot and from one to a large number of flowers are arranged along an unbranched flowering stem. Several attempts have been made to separate Dendrobium into smaller genera, but most have not been accepted by the World Checklist of Selected Plant Families. Dendrobium species are mostly epiphytic, or lithophytic although a few species are terrestrial. They are sympodial herbs with cylindrical roots usually arising from the base of a pseudobulb. The pseudobulbs, when present, are hard, sometimes cane-like, cylindrical or cone-shaped and more or less covered with the bases of the leaves. There are from one to many leaves arranged in two ranks, the leaves varying in shape from linear to oblong, sometimes cylindrical but never channelled or grooved. They are usually much longer than wide and last for only a single season.