The Orchidales include the orchids and three smaller families. Together, they are one of the largest groups of plants, although they are not of particular ecological or economic importance. Vanilla is cultivated for the strong flavor of its fruits; the little black specks in vanilla ice cream are actually the seeds from the orchid. Many kinds of orchids are cultivated and bred for their delicate and often bizarre flowers. The orchid pictured at right above is Phalaenopsis McLellans, a commonly cultivated genus. On the left is Epipactis gigantea, a native California orchid.
Unlike their closest relatives, most orchids have only a single large stamen attached to the pistil to form the gynostemium, visible in the center of an orchid flower. The flowers are bilaterally symmetrical, a necessity for reliable pollination by bees. Many tropical species of orchid will rely on a single species of euglossine bee to pollinate them, and the bee will visit only that particular species of orchid which its kind pollinates. Because of this, the orchid must ensure that its pollen is properly delivered. This is most often achieved by gluing the whole supply of pollen to the visiting bee in a mass called the pollinia. When the bee visits another orchid of the same species, thousands of pollen grains are delivered, allowing the plant to mature thousands of tiny dust-like seeds.
The first orchids were large terrestrial plants, but like bromeliads, orchids took to the trees, where they have diversified to become the largest family of flowering plants. They are able to survive in the treetops in part because many species form mycorrhizal associations with fungi. The fungi increase the area over which the orchid can acquire nutients and water, while the orchid provides food to the fungus which it makes by photosynthesis.
Because orchids are primarily tropical epiphytes and small herbs, they do not have a fossil record. However, like palms and some members of the Iridales, they have plicate (corrugated) leaves, and these leaf forms are among the earliest known fossil monocots.
The Orchidales may be divided into the following families:
The first three families are sometimes put into another order, the Burmanniales, but are still considered the closest relatives of the Orchidaceae, so this separation is largely a matter of opinion. The Orchidales have traditionally been considered the "pinnacle" of monocot evolution, and so are listed last in many floras. This view does not reflect any biologically meaningful information, and so has been abandoned.
For more information about the Orchidales, try Steve Saunders' exhaustive WWW orchid resource list, the Orchidales Resources List at Texas A&M, or the DELTA descriptions for the Burmanniaceae, Corsiaceae, and the Orchidaceae
Extensive horticultural information is available from The Orchid House in Ontario, Canada.
For images of Orchids on the Web, visit Texas A&M Botany, and the University of Wisconsin. View images of Malagasy Orchidaceae at the Missouri Botanical Garden
And Gerry Carr has the only picture of Burmannia I've seen on the web.
Robert L. Dressler. 1981. The Orchids: Natural History and Classification, 332 pp. Harvard University Press, Cambridge.
R. M. T. Dahlgren and H. T. Clifford. 1982. The Monocotyledons: A comparative Study, 378 pp. Academic Press, London and New York.