any member of the family Orchidaceae, a group of attractively flowered plants that composes the order Orchidales. There are from 400 to 800 genera of orchids, with at least 15,000 to as many as 35,000 species.
Orchids are found throughout most of the nonpolar world and are especially abundant in tropical regions. These nonwoody perennial plants grow in soil or on other plants. Those attached to other plants often are vinelike and have a spongy root covering called the velamen that absorbs water from the surrounding air. Most species manufacture their own food, but some live on dead organic material or are helped to obtain nourishment by a fungus living in their roots.
An orchid may have one of two growth patterns, sympodial or monopodial. Most orchids are sympodial; that is, they develop a new stem each year along a horizontal axis. The stem often has a swollen, bulblike region termed a pseudobulb. A monopodial orchid has one erect stem that grows taller each year, adding more leaves and flowers. Flowers are borne singly or in erect or pendent clusters. They range in sizes from about 2 millimetres (about 0.1 inch) to 38 centimetres (15 inches) in diameter.
All orchids have the same bilaterally symmetrical flower structure, with three sepals, but the flowers vary greatly in colour and shape. One of the petals, called the lip, is often distinct in shape and colour from the other petals. The lip usually is the lowest part of the flower, although it is the uppermost part in the developing bud, which turns around its axis as it grows in a process termed resupination. A club-shaped structure in the centre of the flower, known as the column, results from the fusion of male and female reproductive parts. Most orchid species have one stamen at the top of the column, rarely two at the sides. The pollen grains, contained within lobes at the top of the stamen, are grouped into mealy or waxy masses termed pollinia. These packets usually are transferred from one flower to another by insects or birds, although some species are wind- or self-pollinated. Many orchids have highly developed mechanisms (structures, scents, etc.) to ensure cross-pollination between plants. The flowers of some species resemble female insects so closely that male insects try to mate with them (a process called pseudocopulation) and thus carry pollen between flowers.
More than 2,000,000 seeds may be contained in the seedpod produced by a single orchid flower. The size of these seeds caused some botanists to give the orchid order the name Microspermae. An orchid seed contains little nutritive material and needs the help of a fungus to germinate and obtain food.
The only economically important product derived from an orchid is the flavouring agent vanilla, which is obtained from the seedpod of several species of the genus Vanilla. Many folk medicines, local beverages, and foods are prepared from parts of orchid plants.
The ornamental genera Cattleya,
Cymbidium, Vanda, and Laelia are commonly grown for hybridization. Many
thousands of hybrids have been developed for use as garden or greenhouse
ornamentals and in the commercial flower trade. Species of Pleurothallis,
Lepanthes, and Stelis are popular among horticulturists because of their
extremely small size.