Orchids (Family Orchidaceae) are among the most diverse of the flowering plant families, with over 1000 described genera and 15,000 to 20,000 (some sources give 30,000) species, and perhaps another 60,000 hybrids and varieties produced by horticulturalists. They get their name from the Greek orchis, meaning 'testicle', from the appearance of structures called pseudobulbs (defined below) in some species. These monocotyledonous plants are cosmopolitan in distribution, but a majority of the species are perennial epiphytes found in tropical forests. Others are terrestrial herbs, lianas, and a few lack chlorophyll and are saprophytic.
Orchidaceae have many specializations. Best known are the seemingly endless structural variations in the flowers that encourage pollination by particular species of insects, or bats, or birds. Another characteriistic of the family is the production of numerous minute seeds that have a symbiotic relationship with fungi in order to germinate.
All orchids are perennial herbs. Some orchids are terrestrial, growing rooted in the soil. Terrestrial orchids may be rhizomatous, forming corms or tubers.
Pseudobulbs of an epiphytic orchid (enlarge)A great many orchids are epiphytes, growing out of soil on tree branches. Epiphytic orchids have modified aerial roots and an epidermis modified into a spongy, water-absorbing velamen. The base of the stem, or in some species essentially the entire stem, may be thickened to form what is called a pseudobulb.
The basic orchid flower is composed of three sepals and three petals, with the medial petal usually modified and enlarged (then called the labellum or lip), forming a platform near the center of the corolla. In many orchids, the sepals are colored and generally resemble the petals. The reproductive organs in the centre (stamens and pistil) have been transformed into a structure called the column.
It is in the variety of their reproductive methods that orchids truly amaze. The Paphiopedilums (Lady Slippers) have a deep pocket that traps visitors, with just one exit. Passage through this exit leads to pollinia being deposited on the insect. A Eurasian genus has flowers that look so much like female bumble bees that males flying nearby are irresistibly drawn in. An underground orchid in Australia never sees the light of day, but manages to "dupe" ants into pollinating it. The Masdevallia stinks like a rotting carcass, and the forest flies it attracts assist its reproduction. A species discussed briefly by Darwin actually launches its viscid pollen sacs with explosive force. Some Phalaenopsis species in Malaysia are known to use subtle weather cues to coordinate mass flowering.
Fruits and seeds
The orchid ovary is always inferior, three-carpelate and 1 or 3-celled, with parietal placentation (but axile in the Apostasioideae). After pollination, the ovary typically develops into a capsule that is dehiscent by 3 or 6 longitudinal slits, while remaining closed at both ends. The ripening of a capsule can take from 2 to 18 months. Seeds are very numerous (over a million per capsule in some species) and minute.
Almost all the species rely heavily upon mycorrhizal associations with various fungi that decompose surrounding matter, freeing up water-soluble nutrients. Because most orchid seeds are extremely tiny with no food reserves (endosperm lacking), they will not germinate without such a symbiont to supply nutrients in the wild. Horticultural techniques have been devised for germinating seeds on a nutrient-containing gel, eliminating the requirement of the fungus for germination, and greatly aiding the propagation of rare and endangered species. Germination can be extremely slow.
Orchids in commerce
There are a great number of tropical and subtropical orchids, and these are the most commonly known, as they are available at nurseries and through orchid clubs across the world. There are also quite a few orchids which grow in colder climates, although these are less often seen on the market.
Ophrys apifera, bee orchid
Gymnadenia conopsea, fragrant orchid
Anacamptis pyramidalis, pyramidal orchid
Dactylorhiza fuchsii, common spotted orchid
One orchid is used as a foodstuff flavoring, the source of Vanilla see below. The underground tubers of terrestrial orchids are used in the manufacture of ice cream in Turkey, the so-called fox-testicle ice cream. The scent of orchids is frequently used by perfumists (using GLC) to identify potential fragrance chemicals. With these exceptions, orchids have virtually no commercial value other than for the enjoyment of the flowers (see also Botanical Orchids, below).
The family of orchids is remarkably diverse. The plants found in "casual" culture, such as Phalaenopsis, Cattleya, Dendrobium, and so forth, represent a tiny fraction of the thousands of varieties of orchids. Also within the Orchidaceae are "leafless" orchids, which often appear as nothing more than masses of roots, achlorophyllous orchids that are entirely reliant upon their mycorrhizal symbiont for their nutrition, "jewel" orchids with foliage that is as pretty as their flowers, and so many others that are capable of affecting the most dedicated of growers very deeply. Ranging in size from tiny moss-like Pleurothallis species to massive Gramatophyllums (20 feet+) in New Guinea, their beauty and sophistication have captivated many.