orchid, popular name for members of the Orchidaceae, a family of perennial herbs widely distributed in both hemispheres. The unusually large family (of some 450 genera and an estimated 10,000 to 17,500 species) includes terrestrial, epiphytic (see epiphyte), and saprophytic (subsisting on decomposing material) genera. Although the latter may sometimes lack chlorophyll, none is actually parasitic. Orchids grow most abundantly in tropical and subtropical forests, where they are largely epiphytic; the temperate genera thrive in all kinds of shaded habitats except excessively dry or cold ones. Most temperate orchids and all those of Arctic are terrestrial.
A Highly Varied Plant Family
This family of monocotyledonous plants has evolved from prototypes of the lily and amaryllis family and is noteworthy for the wide variety of its highly specialized and curiously modified forms. Epiphytic types have a stem swollen at the base to form a pseudobulb (for food storage) and pendulous aerial roots adapted for water absorption and sometimes containing chlorophyll to make photosynthesis possible. In terrestrial types a symbiotic relationship often exists between the roots and filamentous fungi (mycorrhiza). Horticulturists have found that the presence of certain fungi is necessary for the germination of the minute seeds. Orchid pollen occurs as mealy or waxen lumps of tiny pollen grains, highly varied in form.
The flowers characteristically consist of three petals and three petallike sepals, the central sepal modified into a conspicuous lip (labellum) specialized to secrete nectar that attracts insects. Most of the diverse forms of orchid flowers are apparently complicated adaptations for pollination by specific insects, e.g., the enormous waxflower of Africa, which has a labellum over a foot long and is pollinated by a moth with a tongue of equal length. The saclike labellum of the lady's-slipper serves the same function by forcing the insect to brush against the anther and the stigma (male and female organs) while procuring nectar.
The expensive orchid of the florists' trade is usually the large cattleya; species of this genus (Cattleya) are epiphytic plants native to tropical America. Among the other cultivated orchids are several of the terrestrial rein orchids (genus Habenaria) and many epiphytic tropical genera, e.g., the Asian Dendrobium, with pendant clusters of flowers; Epidendrum, represented in the SE United States by the greenfly orchid; and Odontoglossum, indigenous to the Andes Mts.
About 140 species of orchid are native to North America, usually as bog plants or flowers of moist woodlands and meadows. Species of lady's-slipper, or moccasin flower (Cypripedium) [Lat.,=slipper of Venus], include the pink-blossomed common, or stemless, lady's-slipper (C. acaule) and the showy lady's-slipper (C. reginae), both of the Northeast, and varieties of the yellow lady's-slipper (C. calceolus), which grow in all but the warmest regions of the continent. Other terrestrial genera that grow as American wildflowers are the fringe orchids (Blephariglottis); the small-blossomed twayblades (species of Liparis and Listera); the pogonias, or beard-flowers (Pogonia); the wild pinks, or swamp rose orchids (Arethusa), of northeastern sphagnum bogs; the grass pinks (Limodorum) of eastern bogs and meadows; and the ladies'-tresses, or pearl-twists (Spiranthes), with a distinctive spiral arrangement of yellowish or white flowers. The coral-roots (Corallorhiza), named for the corallike branching of their underground rhizomes, are a nongreen saprophytic genus which includes some North American species. Because orchids are characteristically slow growing and difficult to seed, excessive picking and futile attempts to transplant have depleted native species in some areas.
Orchids are among the most highly prized of ornamental plants. In Mexico the flowers are used symbolically by the natives; each one conveys a sentiment associated with different ceremonies or religious figures. From the time that orchids were first imported from the Bahamas to Britain (in the early 18th cent.) these flowers have been cultivated for their commercial value and have been successfully hybridized and variegated. Many orchids are now propagated by tissue culture methods. Hawaii has become a major center for commercial orchid culture. A species of the Vanilla genus of tropical America is important economically as the source of natural vanilla flavoring.
The orchid family is classified in the division Magnoliophyta, class Liliopsida, order Orchidales.
See R. T. Northen, Home Orchid Growing (3d ed. 1970); M. A. Reinikka, A History of the Orchid (1972).
The plants belonging to the family Orchidaceae represent a pinnacle of evolutionary success in the plant kingdom. Represented by approximately twenty-five thousand species, they are possibly the largest family of flowering plants on Earth. Although orchids are most diverse in the tropics, they are found on every continent except Antarctica and can be found as far north as Alaska and as far south as Tierra del Fuego. Perhaps the main reason that orchids are so successful is that they have developed close relationships with insect pollinators and fungi. Their life histories are extremely complex and intricately woven together across three kingdoms of life: Plantae, Animalia, and Fungi.
Unlike other plants, orchid seeds contain no storage food for their dormant embryos. In order for most orchid seeds to germinate, they must be infected by fungal hyphae . After infection takes place, the orchid is able to take nourishment from the fungus, but it is unclear whether the fungus gets any benefit in return. This life strategy enables orchids to survive in habitats with poor soils, such as bogs, or those that lack soil altogether. Many tropical orchids are epiphytes , and some live completely underground, lacking chlorophyll and depending on fungi for all their nutritional needs.
The close association of orchids with insects was carefully studied by Charles Darwin. Through evolution, orchids have reduced their reproductive organs to one anther and one pistil . Moreover, orchids have fused these two organs into a single structure, the column, and have amassed all of their pollen into a single unit called a pollinium. As a consequence, most orchid flowers have only one chance to pollinate another flower. This strategy may seem risky, but when successful it delivers enough pollen to produce as many as seventy-two thousand seeds. To ensure success, orchids have evolved intricate pollination mechanisms. Some of these include explosive shotguns and glue to attach the pollinium to insects, or floral traps that force bees to take pollen with them when they escape. One of the most fascinating strategies is seen in orchids that not only mimic female wasps in morphology but also produce fragrances similar to female wasp pheromones . These orchids manage to fool male wasps into copulating with their flowers, thereby effecting pollination.
Only one orchid species, Vanilla planifolia, is of significant agricultural value, as the source of natural vanilla flavoring. Cultivation and processing of this spice is a long, labor-intensive process involving pollinating each flower by hand, drying and fermenting the fruits, and extracting the aromatic vanillin flavoring with alcohol. For this reason, natural vanilla is extremely expensive.
Vanilla, however, is not the only orchid of economic value. An enormous industry exists for cut flowers, corsages, and cultivation of orchids by hobbyists. Ancient texts indicate that orchids have been cultivated in China since at least 550 B. C. E. Today, the American Orchid Society alone has more than thirty thousand members, all of whom share a fascination and appreciation of these breathtakingly beautiful flowers. Unfortunately, many orchid species are threatened with extinction because of habitat destruction and over-collecting in the wild. However, all orchids are protected under international treaties.
see also Epiphytes; Horticulture; Interactions, Plant-Insect; Monocots; Pollination Biology.
Kenneth M. Cameron
Cameron, K., et al. "A Phylogenetic Analysis of the Orchidaceae: Evidence from rbc LNucleotide Sequences." American Journal of Botany 86 (1999): 208-24.
Darwin, Charles. The Various Contrivances by Which Orchids Are Fertilised by Insects. London: John Murray, 1888.
Dressler, Robert. The Orchids: Natural History and Classification. Cambridge, MA:Harvard University Press, 1990.
or·chid / ˈôrkid/ • n. a plant (family Orchidaceae ) with complex flowers that are typically showy or bizarrely shaped, having a large specialized lip (labellum) and frequently a spur. Orchids occur worldwide, esp. as epiphytes in tropical forests, and are valuable hothouse plants. DERIVATIVES: or·chid·ist / -ist/ n.