Cronquist, Arthur New York Botanical Garden, New York, New York.
Barkley, Theodore M. Division of Biology, Kansas State University, Manhattan, Kansas.
Last reviewed:January 2021
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An order of flowering plants, division Magnoliophyta (Angiospermae), in the order Asparagales (monocotyledons). The order Orchidales consists of four families: the Orchidaceae, with 20,000–25,000 species; the Burmanniaceae, with more than 100 species; the Cordiaceae, with about 25 species; and the Geosiridaceae, with 1 or 2 species. Members of the Orchidales are mycotrophic, sometimes nongreen plants with very numerous tiny seeds that have an undifferentiated embryo and little or no endosperm. The ovary is always inferior and apparently lacks the septal nectaries found in many monocots, although other kinds of nectaries are present. The various species of Orchidaceae (orchids) have numerous, highly diverse adaptations to particular insect pollinators. The flowers are highly irregular (see illustration) and usually have only one or two stamens, which are adnate to the thickened style. The pollen grains of most genera cohere in large masses called pollinia; thus, a single act of pollination can result in the production of many thousands of seeds. Orchids are most abundant and diversified in moist, tropical regions, where they often grow high above the ground on forest trees. They do not parasitize the trees, but merely roost on them, as epiphytes. The most familiar corsage orchids belong to the genus Cattleya or hybrids of it. See also: Asparagales; Flower; Magnoliophyta; Monocotyledons; Orchid; Pollen; Pollination
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