orchid

Introduction

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Rose pogonia, Pogonia ophioglossoides, a member of the orchid family

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.

Classification

The orchid family is classified in the division Magnoliophyta, class Liliopsida, order Orchidales.

Economic Uses

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.

Orchid Species

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.

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.

Bibliography

See R. T. Northen, Home Orchid Growing (3d ed. 1970); M. A. Reinikka, A History of the Orchid (1972).

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