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Orchids are plants that belong to the family Orchidaceae (), a diverse and widespread group of with blooms that are often colourful and fragrant. Orchids are cosmopolitan plants that are found in almost every habitat on Earth except . The world's species richness diversity of orchid genera and species is found in the tropics.
Orchidaceae is one of the two largest families of flowering plants, along with the Asteraceae. It contains about 28,000 currently accepted species in 702 genera.
The Orchidaceae family encompasses about 6–11% of all species of seed plants. The largest genera are Bulbophyllum (2,000 species), Epidendrum (1,500 species), Dendrobium (1,400 species) and Pleurothallis (1,000 species). It also includes Vanilla (the genus of the vanilla plant), the type genus Orchis, and many commonly cultivated plants such as Phalaenopsis and Cattleya. Moreover, since the introduction of tropical species into cultivation in the 19th century, horticulture have produced many hybrids and .
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Terrestrial orchids may be rhizome or form or . The root caps of terrestrial orchids are smooth and white.
Some sympodial terrestrial orchids, such as Orchis and Ophrys, have two subterranean . One is used as a food reserve for wintry periods, and provides for the development of the other one, from which visible growth develops.
In warm and constantly humid climates, many terrestrial orchids do not need pseudobulbs.
Epiphyte orchids, those that grow upon a support, have modified that can sometimes be a few meters long. In the older parts of the roots, a modified spongy epidermis, called a velamen, has the function of absorbing humidity. It is made of dead cells and can have a silvery-grey, white or brown appearance. In some orchids, the velamen includes spongy and fibrous bodies near the passage cells, called tilosomes.
The cells of the root epidermis grow at a right angle to the axis of the root to allow them to get a firm grasp on their support. Nutrients for epiphytic orchids mainly come from mineral dust, organic detritus, animal droppings and other substances collecting among on their supporting surfaces.
The base of the stem of sympodial epiphytes, or in some species essentially the entire stem, may be thickened to form a pseudobulb that contains nutrients and water for drier periods.
The pseudobulb typically has a smooth surface with lengthwise grooves, and can have different shapes, often conical or oblong. Its size is very variable; in some small species of Bulbophyllum, it is no longer than two millimeters, while in the largest orchid in the world, Grammatophyllum speciosum (giant orchid), it can reach three meters. Some Dendrobium species have long, canelike pseudobulbs with short, rounded leaves over the whole length; some other orchids have hidden or extremely small pseudobulbs, completely included inside the leaves.
With ageing the pseudobulb sheds its leaves and becomes dormant. At this stage it is often called a backbulb. Backbulbs still hold nutrition for the plant, but then a pseudobulb usually takes over, exploiting the last reserves accumulated in the backbulb, which eventually dies off, too. A pseudobulb typically lives for about five years. Orchids without noticeable pseudobulbs are also said to have growths, an individual component of a sympodial plant.
The structure of the leaves corresponds to the specific habitat of the plant. Species that typically bask in sunlight, or grow on sites which can be occasionally very dry, have thick, leathery leaves and the Leaf anatomy are covered by a waxy Plant cuticle to retain their necessary water supply. Shade-loving species, on the other hand, have long, thin leaves.
The leaves of most orchids are perennial, that is, they live for several years, while others, especially those with plicate leaves as in Catasetum, shed them annually and develop new leaves together with new pseudobulbs.
The leaves of some orchids are considered ornamental. The leaves of Macodes sanderiana, a semiterrestrial or rock-hugging ("lithophyte") orchid, show a sparkling silver and gold veining on a light green background. The cordate leaves of Psychopsiella are light brownish-green with maroon-puce markings, created by flower pigments. The attractive mottle of the leaves of lady's slippers from tropical and subtropical Asia ( Paphiopedilum), is caused by uneven distribution of chlorophyll. Also, Phalaenopsis schilleriana is a pastel pink orchid with leaves spotted dark green and light green. The jewel orchid ( Ludisia) is grown more for its colorful leaves than its white flowers.
Some orchids, such as Dendrophylax lindenii (ghost orchid), Aphyllorchis and Taeniophyllum depend on their green roots for photosynthesis and lack normally developed leaves, as do all of the heterotrophy species.
Orchids of the genus Corallorhiza (coralroot orchids) lack leaves altogether and instead have symbiotic or parasitic associations with fungal mycelium, though which they absorb sugars.
The reproductive parts of an orchid flower are unique in that the and style are joined to form a single structure, the column. Instead of being released singly, thousands of pollen grains are contained in one or two bundles called Pollinium that are attached to a sticky disc near the top of the column. Just below the pollinia is a second, larger sticky plate called the stigma.
Pollinators are often visually attracted by the shape and colours of the labellum. However, some Bulbophyllum species attract male fruit flies ( Bactrocera and Zeugodacus spp.) solely via a floral chemical which simultaneously acts as a floral reward (e.g. methyl eugenol, raspberry ketone, or zingerone) to perform pollination. The flowers may produce attractive odours. Although absent in most species, nectar may be produced in a spur of the labellum ( 8 in the illustration above), or on the point of the sepals, or in the septa of the ovary, the most typical position amongst the Asparagales.
In orchids that produce pollinia, pollination happens as some variant of the following sequence: when the pollinator enters into the flower, it touches a viscidium, which promptly sticks to its body, generally on the head or abdomen. While leaving the flower, it pulls the pollinium out of the anther, as it is connected to the viscidium by the caudicle or stipe. The caudicle then bends and the pollinium is moved forwards and downwards. When the pollinator enters another flower of the same species, the pollinium has taken such position that it will stick to the stigma of the second flower, just below the rostellum, pollinating it. In horticulture, Hand-pollination is achieved by removing the pollinia with a small instrument such as a toothpick from the pollen parent and transferring them to the seed parent.
Some orchids mainly or totally rely on self-pollination, especially in colder regions where pollinators are particularly rare. The caudicles may dry up if the flower has not been visited by any pollinator, and the pollinia then fall directly on the stigma. Otherwise, the anther may rotate and then enter the stigma cavity of the flower (as in Holcoglossum amesianum).
The slipper orchid Paphiopedilum parishii reproduces by Self-pollination. This occurs when the anther changes from a solid to a liquid state and directly contacts the stigma surface without the aid of any pollinating agent or floral assembly.
The labellum of the Cypripedioideae is Poke bonnet, and has the function of trapping visiting insects. The only exit leads to the anthers that deposit pollen on the visitor.
In some extremely specialized orchids, such as 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.
Many neotropical orchids are pollinated by male euglossini, which visit the flowers to gather volatile chemicals they require to synthesize pheromone attractants. Males of such species as Euglossa imperialis or Eulaema meriana have been observed to leave their territories periodically to forage for aromatic compounds, such as cineole, to synthesize pheromone for attracting and mating with females. Each type of orchid places the pollinia on a different body part of a different species of bee, so as to enforce proper cross-pollination.
A rare Saprophyte orchid growing entirely underground in Australia, Rhizanthella slateri, is never exposed to light, and depends on and other terrestrial insects to pollinate it.
Catasetum, a genus discussed briefly by Charles Darwin, actually launches its viscid pollinia with explosive force when an insect touches a seta, knocking the pollinator off the flower.
After pollination, the sepals and petals fade and wilt, but they usually remain attached to the ovary.
In 2011, Bulbophyllum nocturnum was discovered to flower nocturnally.
Epipogium aphyllum exhibits a dual reproductive strategy, engaging in both sexual and asexual seed production. The likelihood of apomixis playing a substantial role in successful reproduction appears minimal. Within certain petite orchid species groups, there is a noteworthy preparation of female gametes for fertilization preceding the act of pollination.
The are generally almost microscopic and very numerous, in some species over a million per capsule. After ripening, they blow off like dust particles or spores. Most orchid species lack endosperm in their seed and must enter symbiotic relationships with various mycorrhizal fungi that provide them the necessary nutrients to germinate, so almost all orchid species are mycoheterotrophic during germination and reliant upon fungi to complete their lifecycles. Only a handful of orchid species have seed that can germinate without mycorrhiza, namely the species within the genus Disa with hydrochorous seeds.
As the chance for a seed to meet a suitable fungus is very small, only a minute fraction of all the seeds released grow into adult plants. In cultivation, germination typically takes weeks.
Horticultural techniques have been devised for germinating orchid seeds on an artificial nutrient medium, eliminating the requirement of the fungus for germination and greatly aiding the propagation of ornamental orchids. The usual medium for the sowing of orchids in artificial conditions is agar gel combined with a carbohydrate energy source. The carbohydrate source can be combinations of discrete sugars or can be derived from other sources such as banana, pineapple, peach, or even tomato puree or coconut water. After the preparation of the agar medium, it is poured into test tubes or jars which are then autoclaved (or cooked in a pressure cooker) to sterilize the medium. After cooking, the medium begins to gel as it cools.
Five subfamilies are recognised. The cladogram below was made according to the APG system of 1998. It represents the view that most botanists had held up to that time. It was supported by Plant morphology Research, but never received strong support in molecular phylogenetic studies.
In 2015, a phylogenetic study showed strong statistical support for the following topology of the orchid tree, using 9 Base pair of plastid and Cell nucleus DNA from 7 , a topology that was confirmed by a phylogenomic study in the same year.
Genetic sequencing indicates orchids may have arisen earlier, 76 to 84 million years ago during the Late Cretaceous. "An overview of the Phalaenopsis orchid genome by BAC sequence analysis" (pdf format) . According to Mark W. Chase et al. (2001), the overall biogeography and phylogenetic patterns of Orchidaceae show they are even older and may go back roughly 100 million years.
Using the molecular clock method, it was possible to determine the age of the major branches of the orchid family. This also confirmed that the subfamily Vanilloideae is a branch at the basal dichotomy of the monandrous orchids, and must have evolved very early in the evolution of the family. Since this subfamily occurs worldwide in tropical and subtropical regions, from tropical America to tropical Asia, New Guinea and West Africa, and the continents began to split about 100 million years ago, significant biotic exchange must have occurred after this split (since the age of Vanilla is estimated at 60 to 70 million years). Recent biogeographic studies conducted on densely sampled phylogenies indicated that the most recent common ancestor of all extant orchids probably originated somewhere 83 million years ago in the supercontinent Laurasia. Despite their long evolutionary history on Earth, the extant orchid diversity is also inferred to have originated during the last 5 million years, with the American and Asian tropics as the geographic areas exhibiting the highest speciation rates (i.e., number of speciation events per million years) on Earth.
Genome duplication occurred prior to the divergence of this taxon.
In Middle English, the name bollockwort was used for some orchids, based on "" meaning testicle and "" meaning plant.
Cultivated hybrids in the orchid family are also special in that they are named by using grex nomenclature, rather than nothospecies. For instance, hybrids between Brassavola nodosa and Brassavola acaulis are placed in the grex Brassavola Guiseppi. Brassavola Guiseppi Casa Luna 1968 , BlueNanta. The name of the grex ("Guiseppi" in this example) is written in a non-italic font without quotes.International Code of Nomenclature for Cultivated Plants 9th edition, 2016.
The following list gives a rough overview of their distribution:
Some orchids, such as Neottia and Corallorhiza, lack chlorophyll, so are unable to photosynthesise. Instead, these species obtain energy and nutrients by parasitism soil fungi through the formation of orchid mycorrhizae. The fungi involved include those that form Ectomycorrhizal with trees and other woody plants, parasites such as Armillaria, and . These orchids are known as , but were formerly (incorrectly) described as saprophytes as it was believed they gained their nutrition by breaking down organic matter. While only a few species are achlorophyllous Parasitic plant, all orchids are myco-heterotrophic during germination and seedling growth, and even photosynthetic adult plants may continue to obtain carbon from their fungi. The symbiosis is typically maintained throughout the lifetime of the orchid because they depend on the fungus for nutrients, sugars and minerals.
Orchids of all types have also often been sought by collectors of both species and hybrids. Many hundreds of societies and clubs worldwide have been established. These can be small, local clubs, or larger, national organisations such as the American Orchid Society. Both serve to encourage cultivation and collection of orchids, but some go further by concentrating on conservation or research.
The term "botanical orchid" loosely denotes those small-flowered, tropical orchids belonging to several genera that do not fit into the "florist" orchid category. A few of these genera contain enormous numbers of species. Some, such as Pleurothallis and Bulbophyllum, contain approximately 1700 and 2000 species, respectively, and are often extremely vegetatively diverse. The primary use of the term is among orchid hobbyists wishing to describe unusual species they grow, though it is also used to distinguish naturally occurring orchid species from horticulturally created hybrids.
New orchids are registered with the International Orchid Register, maintained by the Royal Horticultural Society. Several thousand new grexes are registered each year. (2021). 9781911666134, Royal Horticultural Society. ISBN 9781911666134
The underground tubers of terrestrial orchids mainly are ground to a powder and used for cooking, such as in the hot beverage salep or in the Turkish cuisine mastic ice cream dondurma. The name salep has been claimed to come from the Arabic expression , "fox testicles", but it appears more likely the name comes directly from the Arabic name . The similarity in appearance to testes naturally accounts for salep being considered an aphrodisiac.
The dried leaves of Jumellea fragrans are used to flavour rum on Reunion Island.
Some saprophytic orchid species of the group Gastrodia produce potato-like tubers and were consumed as food by native peoples in Australia and can be successfully cultivated, notably Gastrodia sesamoides. Wild stands of these plants can still be found in the same areas as early Aboriginal settlements, such as Ku-ring-gai Chase National Park in Australia. Aboriginal peoples located the plants in habitat by observing where had scratched in search of the tubers after detecting the plants underground by scent.
Orchids native to the Mediterranean are depicted on the Ara Pacis in Rome, until now the only known instance of orchids in ancient art, and the earliest in European art. A French writer and agronomist, Louis Liger, invented a classical myth in his book Le Jardinier Fleuriste et Historiographe published in 1704, attributing it to the ancient Greeks and Romans, in which Orchis the son of a nymph and a satyr rapes a priestess of Dionysus during one of his festivals the Bacchanalia and is then killed and transformed into an orchid flower as punishment by the gods, paralleling the various myths of youths dying and becoming flowers, like Adonis and Narcissus; this myth however does not appear any earlier than Liger, and is not part of traditional Greek and Roman mythologies.
A and B Larsen orchids - Cattleya Hawaian Variable Prasan 336-2.jpg| Cattleya Hawaiian Variable 'Prasan'
File:A and B Larsen orchids - Cattleya Barbara Belle DSCN8696.JPG| Cattlianthe Barbara Belle
File:Cattleya Beaumesnil Parme 1001 Orchids.jpg| Cattleya Beaumesnil 'Parme'
File:A and B Larsen orchids - Cattleya Chocolate Drop x Pao de Acucar 507-21.jpg| Cattlianthe Chocolate Drop x Cattleya Pão de Açúcar
File:Cattleya Empress Frederick C mossiae.jpg| Cattleya mossiae 'Empress Frederick'
File:Cattleya Hermine.jpg|'Hermine'
File:A and B Larsen orchids - Cattleya Little AngelDSCN3349.JPG| Cattleya Little Angel
File:A and B Larsen orchids - Cattleya Marjorie Hausermann York 812-4.jpg| Cattleya Marjorie Hausermann 'York'
File:A and B Larsen orchids - Cattleya Miva Breeze Alize 930-23.jpg|'Miva Breeze Alize'
File:Blc Nobiles carnival.jpg| Rhyncholaeliocattleya 'Nobile's carnival'
File:Cattleya Pernell George Barnett "Yankee Clipper" (3072486817).jpg| Cattleya Pernel George Barnett 'Yankee Clipper'
File:Cattleya Portia.jpg| Cattlianthe Portia
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