Overview

Brief Summary

The Orchidaceae, known as the orchid family, underwent a spectacularly diverse radiation since its late Cretaceous origin 83-75 million years ago to become one of the two most speciose plant families around today (the other being the Asteraceae), and make up more than one third of monocot species (Ramírez et al. 2007; Gustafsson et al. 2010).  Taxonomy of the orchid family is difficult and dynamic, because it is so large (now approximately 27,000+ accepted species) and many new species are described annually (see references listed at the Orchid Tree, Florida Museum of Natural History: http://www.flmnh.ufl.edu/orchidatol/references/orchidATOLrefs.htm; Cameron 1999 and references therein; Williams 2013).  Many morphological and molecular studies break down the family into five monophyletic subfamilies: Apostasioideae, Cypripedioideae, Epidendroideae, Orchidoideae, and Vanilloideae, of which Epidendroideae is by far the largest, containing about 3/5 of orchid species (see references listed at the Orchid Tree, Florida Museum of Natural History: http://www.flmnh.ufl.edu/orchidatol/references/orchidATOLrefs.htm; Cameron 1999 and references therein; Williams 2013; The Plant List 2010). 

Orchids live in nearly all ecosystems around the world except glaciers, true desert and open water, although tropical areas especially in Asia, Africa and the Americas are the hot spots of diversity.  Most grow as epiphytes on other plants, rocks or static objects for support and derive their nutrients and water from the atmosphere and debris, however many species grow in the ground in forest or grassland areas.  Some are parasites of fungi.  Some, such as species in the subfamily Vanilloideae grow as lianas (a woody vine) that can reach sizes up to 20 m. (60 feet) or more in length; the tiny Bulbophyllum minutissimum is only 3-4 mm (0.16-0.2 inches) tall.  (Kew RBG 2013; Williams 2013; Stephens 2013).

Orchids are monocots, perennial herbs with simple leaves and parallel veins, and are well known for the rich diversity of their flower structures. While some have single flowers, most have inflorescences with multiple flowers arranged around a stalk. The flowers are pollinated by insects, in some cases by birds, and it is common for flowers to have petals modified into perches or guides for their pollinators.  Orchids have a dizzying array of pollination syndromes, some fantastically complex.  About a third of orchid species mimic an aspect of their pollinator’s biology in order to trick the pollinator into visiting the flower without providing nectar or other reward.  For example, the bee orchids (genus Ophrys) accurately mimic a female bee, right down to the smell, to entice male visitation.  The flower of Darwin’s orchid, Angraecum sesquipedale, has an extremely long spur with nectar at the end, which led Charles Darwin to posit that this species was pollinated by a moth with a proboscis of unprecedented length.  His theory was validated when the pollinator was discovered, years after Darwin’s death.  In reference to the amazing pollination biology of genus Catasetum, which propel large, sticky pollen capsules at their pollinators, Darwin wrote in a 1861 letter to then director of Kew Gardens, Joseph Hooker: “I was never more interested in any subject in all my life, than in this of orchids” (Williams 2013; Kew RBG 2013; Stevens 2013).

All orchids have inferior ovaries which develop into a capsule with (usually six) compartments containing up to millions of minute seeds (as small as 150 µm), excellent wind dispersers.  One plant typically produces 74 million seeds.  In order to germinate, orchid seeds require a symbiotic interaction with species-specific bascidiomycete fungus, which enters the seed.  This allows the orchid seed, which has no nutrient reserves, to gain necessary nutrients directly from the fungi and form a protocorm, a unique embryonic structure made up of a mass of cells found in no other flowering plants.  After facilitating germination, the colonizing fungal symbiont subsequently nourishes the seedling and especially in the case of epiphytic and parasitic (non-photosynthetic) orchids, the fungal interaction often persists to transfer nutrients and minerals to the fully developed orchid.  It is not clear how the fungi benefit from this interaction.  The orchid apparently controls and regulates the timing and degree of fungal association, presumably providing sufficient reason for the fungi to colonize and re-associate with the plant, often on a seasonal cycle (eResources Unit, 2004; Kew RBG; Stevens 2013; Williams 2013).

The charisma of orchids and their biology have long excited (obsessed!) botanists and the general public alike, and many varieties and hybrids are widely cultivated; this passion has inspired intrepid collecting expeditions and spawned hundreds of orchid societies and clubs around the world, spawning a global cultivation industry worth nine-billion dollars annually.  Each year 3000-4000 new hybrid names enter the International Orchid Register (American Orchid Society 2013).  Most cultivars are tropical or sub-tropical.  Many orchid species are threatened in the wild, due to over collection and habitat degradation.  Cites highly restricts international import/export of orchids; all orchids are on the Appendix II list or higher (Kew RBG 2013; Williams 2013). 

As well as providing significant botanical interest, some orchids have food uses.  Vanilla, for example, is a commercially important and widely used flavoring extracted from the dried pods of several species of genus Vanilla; commercially grown vanilla requires hand pollination of the flower making this is one of the world’s most expensive spices.  Some orchids produce edible tubers; Australian desert and forest orchids, for example, are historically eaten by Aboriginals (Stewart and Percival 1997; The Royal Botanic Gardens and Domain Trust, 2013; Gott 2008).  Orchids also have ancient origins in traditional medicine in many cultures, including Chinese medicine (Bulpitt et al. 2007).

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There are over 21,000 species of orchid. They are likely the largest family of flowering plants. Orchid flowers are special because they grow upside down. A long upper petal grows on the bottom of the flower. This makes a good landing spot for pollinators.

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Comprehensive Description

Description

Perennial, terrestrial or epiphytic herbs with rhizomes, tubers or corms. Stems sometimes swollen at the base (pseudobulbs). Leaves alternate or rarely opposite (e.g. some spp. of Disperis), entire. Inflorescence a spike, raceme or panicle. Flowers bracteate, bisexual, zygomorphic, usually twisted through 180° (resupinate), occasionally not twisted or twisted through 360°. Perianth epigynous; perianth segments 6, usually free, arranged in 2 whorls; both whorls similar or outer whorl (sepals) calyx-like and inner whorl (petals) corolla-like or very reduced. Central segment of outer whorl (dorsal sepal) often different in shape and size to the lateral; central segment of inner whorl (lip or labellum) often lobed or spurred. Stamen 1, united with the style to form the column. Pollen aggregated into masses (pollinia). Ovary inferior, 1-locular. Stigmas 3, fertile or more usually 2 lateral fertile, the other an outgrowth (rostellum), lying between the anthers and the lateral stigmas. Part of the rostellum is often modified into sticky discs (viscidia) to which the pollinia are attached by 1-2 stalks (stipes). Whole structure of pollinia, stipes and viscidia form the pollinarium. Fruit a capsule, often longitudinally ribbed. Seeds minute, very numerous, without endosperm.
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Ecology

Associations

In Great Britain and/or Ireland:
Plant / resting place / on
Anaphothrips orchidaceus may be found on live Orchidaceae

Plant / associate
basidiome of Ceratobasidium cornigerum is associated with mycorrhiza of Orchidaceae

Foodplant / spot causer
Cladosporium dematiaceous anamorph of Cladosporium orchidearum causes spots on live Orchidaceae

Plant / resting place / within
puparium of Delina nigrita may be found in rootstock of Orchidaceae

Foodplant / feeds on
Heliothrips haemorrhoidalis feeds on Orchidaceae

Foodplant / sap sucker
Myzus persicae sucks sap of Orchidaceae

Foodplant / pathogen
Odontoglossum Ringspot virus infects and damages yellowish spotted leaf (young) of Orchidaceae

Foodplant / open feeder
subterranean larva of Otiorhynchus sulcatus grazes on root of Orchidaceae

Foodplant / miner
solitary, then gregarious larva of Parallelomma vittatum mines live leaf of Orchidaceae
Remarks: season: summer

Foodplant / sap sucker
Saissetia coffeae sucks sap of live leaf of Orchidaceae

Foodplant / mycorrhiza
Thanatephorus ochraceus is mycorrhizal with live root of Orchidaceae

Foodplant / feeds on
adult of Thrips tabaci feeds on live leaf of Orchidaceae

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Evolution and Systematics

Functional Adaptations

Functional adaptation

Roots absorb moisture from humid air: orchids
 

Some orchids absorb moisture from humid air via aerial roots.

   
  "Orchids of many kinds have also adopted this high life. They lack the ponds that sustain the bromeliads, so they must collect their nourishment in other ways. Some dangle their roots in the air, absorbing moisture from the humid atmosphere and rely on the tiny amount of nutriments it might have dissolved on its descent through the forest vegetation. Others spread their roots over the surface of the branches and collect the water that has trickled through the leaves and dripped from branch to branch, gathering a little nutriment on the way." (Attenborough 1995:166)
  Learn more about this functional adaptation.
  • Attenborough, D. 1995. The Private Life of Plants: A Natural History of Plant Behavior. London: BBC Books. 320 p.
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Functional adaptation

More successful pollination: orchids
 

The flowers of individual plants of a given orchid species improve the odds for successful pollination by producing a scent unique to that plant.

   
  "However, all individual plants of one species, while they produce a scent that mimics the female pheromone in its essentials, do not smell exactly the same. Each plant differs sufficiently from others to suggest to the bee that this next one, with a slightly different fragrance, will give him the satisfaction that has eluded him so far." (Attenborough 1995:129)
  Learn more about this functional adaptation.
  • Attenborough, D. 1995. The Private Life of Plants: A Natural History of Plant Behavior. London: BBC Books. 320 p.
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Functional adaptation

Pollen fastens to a bee's head: orchids
 

The column of some orchids descends from the top of the flower when a male bee lands and deposits pollinia on its head.

   
  With European orchids, "If and when a male bee finds the flower, he settles upon the lip, grasping it in exactly the same way as he grasps a female bee, and tries to copulate, thrusting the tip of his abdomen into the fringe of long hairs at the end of the lip. He fails, of course, but in the process, a curved column that houses both male and female organs, descends from the top of the orchid and glues a pair of pollinia to his head. If the next orchid he visits has already despatched its pollinia, then the column will pick up the one he carries and the orchid is fertilised." (Attenborough 1995:126)
  Learn more about this functional adaptation.
  • Attenborough, D. 1995. The Private Life of Plants: A Natural History of Plant Behavior. London: BBC Books. 320 p.
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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage

Barcode of Life Data Systems (BOLD) Stats
Specimen Records: 15293
Specimens with Sequences: 11893
Specimens with Barcodes: 9137
Species: 5474
Species With Barcodes: 4371
Public Records: 7230
Public Species: 3238
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Statistics of barcoding coverage: Orchidaceae Jorge219

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 1
Species With Barcodes: 1
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Statistics of barcoding coverage: Orchidaceae Jorge218

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 1
Species With Barcodes: 1
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Statistics of barcoding coverage: Orchidaceae A.guadamuz310

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 3
Species With Barcodes: 1
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Statistics of barcoding coverage: Orchidaceae Espinoza5739

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 4
Species With Barcodes: 1
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Statistics of barcoding coverage: Orchidaceae Jorge171

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 1
Species With Barcodes: 1
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Barcode data

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Wikipedia

Orchidaceae

"Orchid" redirects here. For other uses, see Orchid (disambiguation).

Orchidaceae is a diverse and widespread family of flowering plants with blooms that are often colourful and often fragrant, commonly known as the orchid family. Along with the Asteraceae, they are one of the two largest families of flowering plants, with between 21,950 and 26,049 currently accepted species, found in 880 genera.[2][3] The determination of which family is larger is still under debate, because verified data on the members of such enormous families are continually in flux. Regardless, the number of orchid species nearly equals the number of bony fishes and more than twice the number of bird species, and about four times the number of mammal species. The family also encompasses about 6–11% of all seed plants.[4] 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 Vanilla (the genus of the vanilla plant), Orchis (type genus), and many commonly cultivated plants such as Phalaenopsis and Cattleya. Moreover, since the introduction of tropical species into cultivation in the 19th century, horticulturists have produced more than 100,000 hybrids and cultivars.

Etymology[edit]

The type genus (i.e. the genus after which the family is named) is Orchis. The genus name comes from the Ancient Greek ὄρχις (órkhis), literally meaning "testicle", because of the shape of the twin tubers in some species of Orchis.[5][6] The term "orchid" was introduced in 1845 by John Lindley in School Botany,[citation needed] as a shortened form of Orchidaceae.[7]

Description[edit]

Orchids are easily distinguished from other plants, as they share some very evident apomorphies. Among these are: bilateral symmetry (zygomorphism), many resupinate flowers, a nearly always highly modified petal (labellum), fused stamens and carpels, and extremely small seeds.

Stem and roots[edit]

All orchids are perennial herbs, lack any permanent woody structure, and can grow according to two patterns:

  • Monopodial: The stem grows from a single bud, leaves are added from the apex each year and the stem grows longer accordingly. The stem of orchids with a monopodial growth can reach several metres in length, as in Vanda and Vanilla.
  • Sympodial: Sympodial orchids have a front (the newest growth) and a back (the oldest growth).[8] The plant produces a series of adjacent shoots which grow to a certain size, bloom and then stop growing, to be then replaced. Sympodial orchids grow laterally rather than vertically, following the surface of their support. The growth continues by development of new leads, with their own leaves and roots, sprouting from or next to those of the previous year, as in Cattleya. While a new lead is developing, the rhizome may start its growth again from a so-called 'eye', an undeveloped bud, thereby branching. Sympodial orchids may have visible pseudobulbs joined by a rhizome, which creeps along the top or just beneath the soil.
Anacamptis lactea showing the two tubers

Terrestrial orchids may be rhizomatous or form corms or tubers. The root caps of terrestrials are smooth and white.

Some sympodial terrestrials, such as Orchis and Ophrys, have two subterranean tuberous roots. 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 humid climates, many terrestrial orchids do not need pseudobulbs.

Epiphytic orchids have modified aerial roots that can sometimes be a few meters long. In the older parts of the roots, a modified spongy epidermis, called velamen, has the function to absorb 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 mainly come from animal droppings and other organic detritus on their supporting surfaces.

The pseudobulb of Prosthechea fragrans

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 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.

Leaves[edit]

Like most monocots, orchids generally have simple leaves with parallel veins, although some Vanilloideae have a reticulate venation. Leaves may be ovate, lanceolate, or orbiculate, and very variable in size. Their characteristics are often diagnostic. They are normally alternate on the stem, often plicate, and have no stipules. Orchid leaves often have siliceous bodies called stegmata in the vascular bundle sheaths (not present in the Orchidoideae) and are fibrous.

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 laminae are covered by a waxy cuticle to retain their necessary water supply. Shade 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, shed them annually and develop new leaves together with new pseudobulbs, as in Catasetum.

The leaves of some orchids are considered ornamental. The leaves of the Macodes sanderiana, a semiterrestrial or lithophyte, show a sparkling silver and gold veining on a light green background. The cordate leaves of Psychopsiella limminghei 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 discolor) is grown more for its colorful leaves than its white flowers.

Some orchids, 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 heterotrophic species.

Orchids of the genus Corallorhiza (coralroot orchids) lack leaves altogether and instead wrap their roots around the roots of mature trees and use specialized fungi to harvest sugars.[9]

Flowers[edit]

Orchidaceae are well known for the many structural variations in their flowers.

Cattleya cultivar
Vanda cultivar

Some orchids have single flowers, but most have a racemose inflorescence, sometimes with a large number of flowers. The flowering stem can be basal, that is, produced from the base of the tuber, like in Cymbidium, apical, meaning it grows from the apex of the main stem, like in Cattleya, or axillary, from the leaf axil, as in Vanda.

As an apomorphy of the clade, orchid flowers are primitively zygomorphic (bilaterally symmetrical), although in some genera like Mormodes, Ludisia and Macodes, this kind of symmetry may be difficult to notice.

The orchid flower, like most flowers of monocots, 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, 1), but may be completely distinct.

The upper medial petal, called the labellum or lip (6), is always modified and enlarged. The inferior ovary (7) 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.

The normal form of the sepals can be found in Cattleya, where they form a triangle. In Paphiopedilum (Venus slippers), the lower two sepals are fused into a synsepal, while the lip has taken the form of a slipper. In Masdevallia, all the sepals are fused.

Orchid flowers with abnormal numbers of petals or lips are called peloric. Peloria is a genetic trait, but its expression is environmentally influenced and may appear random.

Longitudinal section of a flower of Vanilla planifolia

Orchid flowers primitively had three stamens, but this situation is now limited to the genus Neuwiedia. Apostasia and the Cypripedioideae have two stamens, the central one being sterile and reduced to a staminode. All of the other orchids, the clade called Monandria, retain only the central stamen, the others being reduced to staminodes (4). The filaments of the stamens are always adnate (fused) to the style to form cylindrical structure called the gynostemium or column (2). In the primitive Apostasioideae, this fusion is only partial; in the Vanilloideae, it is more deep; in Orchidoideae and Epidendroideae, it is total. The stigma (9) is very asymmetrical, as all of its lobes are bent towards the centre of the flower and lie on the bottom of the column.

Pollen is released as single grains, like in most other plants, in the Apostasioideae, Cypripedioideae and Vanilloideae. In the other subfamilies, that comprise the great majority of orchids, the anther (3), carries and two pollinia.

A pollinium is a waxy mass of pollen grains held together by the glue-like alkaloid viscin, containing both cellulosic strands and mucopolysaccharides. Each pollinium is connected to a filament which can take the form of a caudicle, as in Dactylorhiza or Habenaria, or a stipe, as in Vanda. Caudicles or stipes hold the pollinia to the viscidium, a sticky pad which sticks the pollinia to the body of pollinators.

At the upper edge of the stigma of single-anthered orchids, in front of the anther cap, there is the rostellum (5), a slender extension involved in the complex pollination mechanism.

As aforementioned, the ovary is always inferior (located behind the flower). It is three-carpelate and one or, more rarely, three-partitioned, with parietal placentation (axile in the Apostasioideae).

In 2011, a member of the genus Bulbophyllum, Bulbophyllum nocturnum, was discovered to flower nocturnally.[10]

Fruits and seeds[edit]

Cross-sections of orchid capsules showing the longitudinal slits

The ovary typically develops into a capsule that is dehiscent by three or six longitudinal slits, while remaining closed at both ends.

The seeds 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. They lack endosperm and must enter symbiotic relationships with various mycorrhizal basidiomyceteous fungi that provide them the necessary nutrients to germinate, so that all orchid species are mycoheterotrophic during germination and reliant upon fungi to complete their lifecycles.

Closeup of a Phalaenopsis blossom

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 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 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.

Pollination[edit]

The complex mechanisms which orchids have evolved to achieve cross-pollination were investigated by Charles Darwin and described in his 1862 book Fertilisation of Orchids. Orchids have developed highly specialized pollination systems, thus the chances of being pollinated are often scarce, so orchid flowers usually remain receptive for very long periods, and 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. However, some Bulbophyllum species attract male fruit flies (Bactrocera spp.) solely via a floral chemical which simultaneously acts as a floral reward (e.g. methyl eugenol, raspberry ketone or zingerone) to perform pollination.[11][12][13] The flowers may produce attractive odours. Although absent in most species, nectar may be produced in a spur (8) of the labellum, 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. 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. The possessors of orchids may be able to reproduce the process with a pencil, small paintbrush, or other similar device.

Ophrys apifera is about to self-pollinate

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 labellum of the Cypripedioideae is poke-shaped, and has the function to trap 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 orchid bees, which visit the flowers to gather volatile chemicals they require to synthesize pheromonal attractants. 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.

An underground orchid in Australia, Rhizanthella slateri, is never exposed to light, and depends on ants and other terrestrial insects to pollinate it.

Catasetum, a genus discussed briefly by 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.

Asexual reproduction[edit]

Some species, such as Phalaenopsis, Dendrobium and Vanda, produce offshoots or plantlets formed from one of the nodes along the stem, through the accumulation of growth hormones at that point. These shoots are known as keiki.

Taxonomy[edit]

The taxonomy of this family is in constant flux, as new studies continue to identify more classificatory elements. The Orchidaceae is currently placed in the order Asparagales by the APG III system of 2009.[1]

Five subfamilies are recognised. The cladogram has been made according to the APG system:



Apostasioideae: 2 genera and 16 species, south-western Asia




Cypripedioideae: 5 genera and 130 species, from the temperate regions of the world, as well as tropical America and tropical Asia


 Monandrae 

Vanilloideae: 15 genera and 180 species, humid tropical and subtropical regions, eastern North America




Epidendroideae: more than 500 genera and more or less 20,000 species, cosmopolitan



Orchidoideae: 208 genera and 3,630 species, cosmopolitan






Evolution[edit]

A study in the scientific journal Nature has hypothesized that the origin of orchids goes back much longer than originally expected.[14] An extinct species of stingless bee, Proplebeia dominicana, was found trapped in Miocene amber from 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.[14] The extinct orchid M. caribea has been placed within the extant tribe Cranichideae, subtribe Goodyerinae (subfamily Orchidoideae).

This indicates orchids may have arisen 76 to 84 million years ago during the Late Cretaceous.[15] In other words, they may have coexisted with dinosaurs. It also shows insects were active pollinators of orchids then. According to 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.[16]

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 genus 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).

Genera[edit]

The following are amongst the most notable genera of the orchid family:[citation needed]

Distribution[edit]

Orchidaceae are cosmopolitan, occurring in almost every habitat apart from glaciers. The world's richest diversity of orchid genera and species is found in the tropics, but they are also found above the Arctic Circle, in southern Patagonia, and two species of Nematoceras on Macquarie Island at 54° south.

The following list gives a rough overview of their distribution:[citation needed]

  • Oceania: 50 to 70 genera
  • North America: 20 to 26 genera
  • tropical America: 212 to 250 genera
  • tropical Asia: 260 to 300 genera
  • tropical Africa: 230 to 270 genera
  • Europe and temperate Asia: 40 to 60 genera

Ecology[edit]

A majority of orchids are perennial epiphytes, which grow anchored to trees or shrubs in the tropics and subtropics. Species such as Angraecum sororium are lithophytes,[17] growing on rocks or very rocky soil. Other orchids (including the majority of temperate Orchidaceae) are terrestrial and can be found in habitat areas such as grasslands or forest.

Some orchids, such as Neottia and Corallorhiza, lack chlorophyll, so 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.[18] These orchids are known as myco-heterotrophs, 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 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.

Uses[edit]

A flower of a Blc. Paradise Jewel 'Flame' hybrid orchid plant. Blooms of the Cattleya alliance are often used in ladies' corsages.

The scent of orchids is frequently analysed by perfumers (using headspace technology and gas-liquid chromatography) to identify potential fragrance chemicals.

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. Temperate species available at nurseries include Ophrys apifera (bee orchid), Gymnadenia conopsea (fragrant orchid), Anacamptis pyramidalis (pyramidal orchid) and Dactylorhiza fuchsii (common spotted orchid).

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 such as the Sutherland Shire Orchid Society, 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 (not necessarily related to each other) 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.

Use as food[edit]

Further information: Vanilla
Vanilla fruits drying

The dried seed pods of one orchid genus, Vanilla (especially Vanilla planifolia), are commercially important as flavoring in baking, for perfume manufacture and aromatherapy.

The underground tubers of terrestrial orchids [mainly Orchis mascula (early purple orchid)] are ground to a powder and used for cooking, such as in the hot beverage salep or in the Turkish frozen treat dondurma. The name salep has been claimed to come from the Arabic expression ḥasyu al-tha`lab, "fox testicles", but it appears more likely the name comes directly from the Arabic name saḥlab. The similarity in appearance to testes naturally accounts for salep being considered an aphrodisiac.

The dried leaves of Jumellea fragrans are used to flavor 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 bandicoots had scratched in search of the tubers after detecting the plants underground by scent.[Note 1]

Traditional medicinal uses[edit]

Orchids have been used in traditional medicine in an effort to treat many diseases and ailments. They have been used as a source of herbal remedies in China since 2800 BC. Gastrodia elata is one of the three orchids listed in the earliest known Chinese Materia Medica (Shennon bencaojing) (c. 100 AD). Theophrastus mentions orchids in his Enquiry into Plants (372–286 BC).

Cultural symbolism[edit]

Orchids have many associations with symbolic values. For example, the orchid is the City Flower of Shaoxing, China. Cattleya mossiae is the national Venezuelan flower, while Cattleya trianae is the national flower of Colombia. Vanda 'Miss Joaquim' is the national flower of Singapore. Guarianthe skinneri is the national flower of Costa Rica. 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.[Note 2]

See also[edit]

Notes[edit]

  1. ^ Early western district (Vic.) settler gives account of local Aboriginal people gathering potato orchid tubers, digging where bandicoots had scratched.[19]
  2. ^ The symbolic (or even religious) meaning of the Ara Pacis orchids is not yet known.[20]

References[edit]

  1. ^ a b Angiosperm Phylogeny Group (2009). "An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG III" (PDF). Botanical Journal of the Linnean Society 161 (2): 105–121. doi:10.1111/j.1095-8339.2009.00996.x. Retrieved 26 June 2013. 
  2. ^ P. F. Stevens (June 2008). "Angiosperm Phylogeny Website Version 9". Missouri Botanical Garden. Retrieved 26 May 2013. 
  3. ^ "WCSP". World Checklist of Selected Plant Families. Retrieved 2010. 
  4. ^ Yohan Pillon & Mark W. Chase (2007). "Taxonomic exaggeration and its effects on orchid conservation". Conservation Biology 21 (1): 263–265. doi:10.1111/j.1523-1739.2006.00573.x. PMID 17298532. 
  5. ^ Joan Corominas (1980). Breve Diccionario Etimológico de la Lengua Castellana. Ed. Gredos. p. 328. ISBN 84-249-1332-9. 
  6. ^ Hyam, R. & Pankhurst, R.J. (1995). Plants and their names : a concise dictionary. Oxford: Oxford University Press. ISBN 978-0-19-866189-4. 
  7. ^ Grigson, G. (1973). A Dictionary of English Plant Names. London: Allen Lane. ISBN 0-7139-0442-9. 
  8. ^ Nash, N., & Frownie, S. (2008). Complete guide to orchids. (p. 12). Meredith Publishing Group.
  9. ^ Jenny King. "The coralroot orchid". Orchids in Northern Washington State. Silvercrown Mountain Outdoor School. Retrieved 10 June 2011. 
  10. ^ Tom Lawrie. "World's first night-flowering orchid discovered". Australian Geographic date=23 November 2010. Retrieved 26 May 2013. 
  11. ^ Tan, K.H. and R. Nishida (2000) Mutual reproductive benefits between a wild orchid, Bulbophyllum patens, and Bactrocera fruit flies via a floral synomone. Journal of Chemical Ecology 26: 533-546
  12. ^ Tan, K.H., R. Nishida and Y.C. Toong (2002) Floral synomone of a wild orchid, Bulbophyllum cheiri, lures Bactrocera fruit flies for pollination. Journal of Chemical Ecology 28:1161-1172.
  13. ^ Tan, K.H. and R. Nishida (2005) Synomone or Kairomone? - Bulbophyllum apertum (Orchidaceae) flower releases raspberry ketone to attract Bactrocera fruit flies. Journal of Chemical Ecology. 31(3): 509-519.
  14. ^ a b Santiago R. Ramírez, Barbara Gravendeel, Rodrigo B. Singer, Charles R. Marshall & Naomi E. Pierce (30 August 2007). "Dating the origin of the Orchidaceae from a fossil orchid with its pollinator". Nature 448 (7157): 1042–1042. doi:10.1038/nature06039. PMID 17728756. 
  15. ^ http://ir.lib.ncku.edu.tw/bitstream/987654321/108263/2/An%20overview%20of%20the%20Phalaenopsis%20orchid%20genome%20by%20BAC%20end%20sequence%20analysis.pdf
  16. ^ Mark W. Chase (2001). "The origin and biogeography of Orchidaceae". In A. M. Pridgeon, P. J. Cribb, M. W. Chase & F. Rasmussen. Orchidoideae (Part 1). Genera Orchidacearum 2. Oxford University Press. pp. 1–5. ISBN 978-0-19-850710-9. 
  17. ^ Melissa Whitman, Michael Medler, Jean Jacques Randriamanindry & Elisabeth Rabakonandrianina (2011). "Conservation of Madagascar's granite outcrop orchids: influence of fire and moisture". Lankesteriana 11 (1): 55–67. 
  18. ^ Jonathan R. Leake (2005). "Plants parasitic on fungi: unearthing the fungi in myco-heterotrophs and debunking the 'saprophytic' plant myth". Mycologist 19 (3): 113–122. doi:10.1017/S0269915X05003046. 
  19. ^ Dawson in Zola & Gott, 1992:38[citation needed]
  20. ^ Jarrett A. Lobelli (2012). "The Emperor's orchids". Archaeology 66 (1): 16. Archived from the original on 13 December 2012. 
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