Orchidaceae, the Orchid family, is the largest family of the flowering plants (Angiospermae). Its name is derived from the genus Orchis.
The Royal Botanical Gardens of Kew list 880 genera and nearly 22,000 accepted species, but the exact number is unknown (perhaps as many as 25,000) because of taxonomic disputes. The number of orchid species equals about four times the number of mammal species, or more than twice the number of bird species. It also encompasses about 6–11% of all seed plants. About 800 new orchid species are added each year. The largest genera are Bulbophyllum (2,000 species), Epidendrum (1,500 species), Dendrobium (1,400 species) and Pleurothallis (1,000 species). The family also includes the Vanilla (the genus of the vanilla plant), Orchis (type genus) and many commonly cultivated plants like some Phalaenopsis or Cattleya.
Moreover, since the introduction of tropical species in the 19th century, horticulturists have produced more than 100,000 hybrids and cultivars.
The complex mechanisms which orchids evolve to achieve cross-pollination were investigated by Charles Darwin and described in his 1862 book Fertilisation of Orchids.
Orchidaceae are cosmopolitan, occurring in almost every habitat apart from deserts and glaciers. The great majority are to be found in the tropics, mostly Asia, South America and Central America, but they are also found above the Arctic Circle, in southern Patagonia and even on Macquarie Island, close to Antarctica.
This family is totally recognised, and the APG II system of 2003 places it in the order Asparagales. The taxonomy of this family is in constant flux, as new studies continue to identify more classificatory elements. Five subfamilies are now recognised.
Ecology: A majority of orchids are perennial epiphytes, which grow anchored to trees or shrubs in the tropics and subtropics. Other species are lithophytes, growing on rocks or very rocky soil, or are terrestrial. Nearly all temperate orchids are terrestrial. Some orchids, like Neottia and Corallorhiza, lack chlorophyll and are unable to photosynthesize. Instead, these species obtain energy and nutrients by parasitising soil fungi through the formation of orchid mycorrhizas. The fungi involved include those that form ectomycorrhizas with trees and other woody plants, parasites such as Armillaria, and saprotrophs. These orchids are known as myco-heterotrophs, but were formerly (incorrectly) described as saprophytes due to the belief that they gained their nutrition by breaking down organic matter. While only a few species are achlorophyllous holoparasites, all orchids are myco-heterotrophic during germination and seedling growth and even photosynthetic adult plants may continue to obtain carbon from their mycorrhizal fungi.
The orchid flower has two whorls of sterile elements. The outer whorl has three sepals and the inner whorl has three petals. The sepals are usually very similar to the petals (and thus called tepals), but may be completely distinct. The upper medial petal, called the labellum or lip, is always modified and enlarged. The inferior ovary or the pedicel usually rotates 180 degrees, so that the labellum, goes on the lower part of the flower, thus becoming suitable to form a platform for pollinators. This characteristic, called resupination occurs primitively in the family and is considered apomorphic (the torsion of the ovary is very evident from the picture). Some orchids have secondarily lost this resupination, e. g. Zygopetalum and Epidendrum secundum.
Pollination: Orchids have developed highly specialized pollination systems and thus the chances of being pollinated are often scarce. This is why orchid flowers usually remain receptive for very long periods and why most orchids deliver pollen in a single mass; each time pollination succeeds thousands of ovules can be fertilized.
Pollinators are often visually attracted by the shape and colours of the labellum. The flowers may produce attractive odours. Although absent in most species, nectar may be produced in a spur of the labellum, on the point of the sepals or in the septa of the ovary, the most typical position amongst the Asparagales.
In some extremely specialized orchids, like the Eurasian genus Ophrys, the labellum is adapted to have a colour, shape and odour which attracts male insects via mimicry of a receptive female. Pollination happens as the insect attempts to mate with flowers.
Evolution: A study in the scientific journal Nature (Nature 448: 1042–1042) has hypothesized that the origin of orchids goes back much longer than originally expected. An extinct species of stingless bee, Proplebeia dominicana, was found trapped in Miocene amber about 15-20 million years ago. The bee was carrying pollen of a previously unknown orchid taxon, Meliorchis caribea, on its wings. This find is the first evidence of fossilised orchids to date.
Uses: One orchid genus, Vanilla, is commercially important, used as a flavouring. The underground tubers of terrestrial orchids (mainly Early Purple Orchid) are ground to a powder and used for cooking, such as in the hot beverage salep or in a Turkish ice-cream. The other important use of orchids is their cultivation for the enjoyment of the flowers. Most cultivated orchids are tropical or subtropical, but quite a few which grow in colder climates can be found on the market.
Orchids of all types have also often been sought by collectors of both species and hybrids. As such many hundreds of societies and clubs worldwide have been established. These can be small local clubs like Sutherland Shire Orchid Society or larger national organisations like American Orchid Society. Both serve to encourage cultivation and collection of orchids, but some go further by concentrating on conservation or research.
Topics of Interest
The Bee Orchid (Ophrys apifera) is a perennial, temperate climate species of orchid generally found growing on semi-dry turf, on limestone, calcareous dunes or in open areas in woodland. The Bee Orchid is a common plant in the Mediterranean region eastwards to the Black Sea but is less common in its northern range being uncommon or local in Germany and Ireland. In the UK it has a distinct south-eastern preference, being more common in England, whereas it is only to be found in coastal regions of Wales and some parts of Northern Ireland. In Scotland it was thought to be extinct, but was rediscovered in Ayrshire in 2003. In some countries the plants have protected status. They are unusual in that in some years they appear in great numbers, then sometimes only reappear after an absence of many years.
This hardy orchid grows to a height of 30 cm. They live in a symbiotic relationship with mycorrhiza ( a soil-dwelling fungus).
Bees in the past have promoted the evolution of bee orchids. Male bees, over many generations of cumulative orchid evolution, have built up the bee-like shape through trying to copulate with flowers, and hence carrying pollen.
The Orchid Grower is A Juvenile Science Adventure Novel by Julian T. Rubin from Zumaya Publications
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