| Orchidaceae Fossil range: 80 Ma Late Cretaceous - Recent |
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| Color plate from Ernst Haeckel's Kunstformen der Natur | |
| Scientific classification | |
| Kingdom: | Plantae |
| (unranked): | Angiosperms |
| (unranked): | Monocots |
| Order: | Asparagales |
| Family: | Orchidaceae Juss. |
| Subfamilies | |
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| Distribution range of family Orchidaceae | |
Orchidaceae, the Orchid family, is the largest family of the flowering plants (Angiospermae).[1][2] 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)[3] 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.[4] About 800 new orchid species are described 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.
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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.
The following list gives a rough overview of their distribution:
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. The cladogram has been made according to the APG system:
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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.[5] 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.
Orchids are easily distinguished, as they share some very evident apomorphies. Among these: bilaterally symmetric (zygomorphic), many resupinate, one petal (labellum) is always highly modified, stamens and carpels are fused, and the seeds are extremely small.
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 laminas 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 fairly inconspicuous 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.
All orchids are perennial herbs and lack any permanent woody structure. Orchids can grow according to two patterns:
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. These structures are named 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 surface.
The base of the stem of sympodial epiphytes, or in some species essentially the entire stem, may be thickened to form what is called 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 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. A pseudobulb then takes over, exploiting the last reserves accumulated in the backbulb, which eventually dies off too. A pseudobulb typically lives for about five years.
Orchidaceae are well known for the many structural variations in their flowers.
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, 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 together 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.
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, while 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 lay 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 stands and mucopolysaccharides. Each pollinium is connected to a filament which can take the form of a caudicle, like in Dactylorhiza or Habenaria or a stipe, like 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).
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 (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.
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 hasn't been visited by any pollinator and the pollina 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, 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.
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, never sees the light of day 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.
Some species, as some 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.
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 2 to 18 months.
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 relationship 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 lifecycle.
As the chance for a seed to meet a fitting fungus is very small, only a minute fraction of all the seeds released grow into an adult plant. In cultivation, germination typically takes weeks, while there is a report of one paphiopedilum that took fifteen years.
Horticultural techniques have been devised for germinating seeds on a nutrient-containing gel, eliminating the requirement of the fungus for germination, greatly aiding the propagation of ornamental orchids.
The main component for the sowing of orchids in artificial conditions is the agar agar. The substance is put together with some type of carbohydrate (actually, some kind of glucose) which provides qualitative organic feed. Such substance may be banana, pineapple, peach or even tomato puree or coconut milk. After the cooking of the agar agar (it has to be cooked in sterile conditions) the mix is poured into test tubes or jars where the substance begins to jelly. The seeds have to be put in the dish above boiling water, in the steam because that secures sterile conditions. The test tubes are put diagonally after that.
A study in the scientific journal Nature [6] 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 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.[6]
The extinct orchid M. caribea has been placed within the extant tribe Cranichideae, subtribe Goodyerinae (subfamily Orchidoideae).
This indicates that orchids may have an ancient origin and have arisen 76 to 84 million years ago during the Late Cretaceous. In other words, they may have co-existed with dinosaurs. It shows also that at that time insects were active pollinators of orchids. According to M.W. Chase et al. (2001) the overall biogeography and phylogenetic patterns of Orchidaceae show that they are even older and may go back roughly 100 million years [7]
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).
One orchid genus, Vanilla, is commercially important, used as a flavouring.
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 ice-cream (Dondurma - salepli dondurma). It has been claimed that the name salep comes from the Arabic expression ḥasyu al-tha`lab "fox testicles",however, it appears more likely that the Turkish name salep 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 flavour rum on Reunion Island.
The scent of orchids is frequently analysed by perfumists (using 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 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.
The term botanical orchid loosely denotes those small flowered tropical orchids belonging to several genera (not necessarily related to each other) that don't 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.
A few of the most common orchids found in "casual" culture are:
The National Orchid Garden in the Singapore Botanic Gardens is considered by some to be among the finest collections of orchids in cultivation open to the public.[citation needed]
Orchids, like tulips, have become a major market throughout the world. Buyers now bid hundreds of dollars on new hybrids or improved ones. Because of their apparent ease in hybridization, they are now becoming one of the most popular cut-flowers on the market.[citation needed]
The following are amongst the most notable genera of the orchid family:
 Corallorhyza maculata, a myco-heterotroph |
 Cephalanthera longifolia, a terrestrial orchid |
 Leaves of different species of orchids |
 Habenaria radiata. Note the lip |
 Pterostylis coccinea, a highly specialized shape |
 Neuwiedia griffithii, Apostasioideae. Note the three normal stamens. |
 Cypripedium acaule has two stamens. One can be seen from the picture, the other is on the other side |
 Catasetum fimbriatum. The seta is evident. |
 Holcoglossum kimballianum |
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 Vanilla plant (the climber) |
 Cultivated Epidendrum ciliare |
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 Listera ovata, a less showy orchid |
 Vanda tricolor var. suavis |
 Oncidium papilio |
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 Cambria |
 Phalaenopsis hybrid |
 Orchids at a flower show in Tatton Park, Cheshire, England, 24 July 2008 |
 Renanthera storei |
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 Cattleya aclandiae. There is the typical zygomorphic flower with three petal-like sepals (top, lower right, lower left), two normal petals on either side and the labellum. |
 An orchid Leaf. |
 Orchid on display at American Orchid Society, Delray Beach |
 purple orchids at American Orchid Society, Delray Beach, FL |
 Orchid at Am. Orchid Soc Delray Bch |
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ORCHIDS. The word Orchis is used in a special sense to denote a particular genus of the Orchid family (Orchidaceae); very frequently, also, it is employed in a more general way to indicate any member of that large and very interesting group. It will be convenient here to use the word Orchis as applying to that particular genus which gives its name to the order or family, and to employ the term "orchid" in the less precise sense.
The flowers of all orchids, though extremely diverse within certain limits, and although superficially very different from those of other monocotyledons, are ° 1' all formed upon one common plan, which is only a modification of that observable in such flowers as those of the narcissus s ate/ S `? „, or snowdrop (Galanthus) . The conformation of those flowers a consists essentially in the pres- ' 'A B ence of a six-parted perianth, the three outer segments of which correspond to a calyx, the three inner ones to a corolla. These segments spring apparently from the top of the ovary - the real explanation, however, being that the end of the flower-stalk or "thalamus," as it grows, becomes dilated into a sort of cup or tube enclosing and indeed closely adhering to the ovary, so that the latter organ appears to be beneath the perianth instead of above it as in a lily, an appearance which has given origin to the term "inferior ovary." Within the perianth, and springing from its sides, or apparently from the top of the ovary, are six stamens whose anthers contain pulverulent pollen-grains. These stamens encircle a style which is the upward continuation of the ovary, and which shows at its free end traces of the three originally separate but now blended carpels of which the ovary consists. An orchid flower has an inferior ovary like that just s, sl -- --s[ ! FIG. 2. - Diagram of the flower FIG. 3. - Flower of Orchis. of Orchis. s, s, s, The three outer s, sl, sl, The three divisions of divisions of the the outer perianth. perianth.
p1, pl, The two lateral divisions p, p,1, The three inner, of the inner perianth. 1 being the label ps, The superior division or lum, here inferior the labellum, which may by the twisting become inferior by the of the ovary.
twisting of the ovary. e, Spur of the label e, The fertile stamen, with lum.
its two pollen-masses in o, The twisted ovary.
the anther-lobes. st, The stigma.
c, The one-celled ovary cut a, The anther, con transversely, having three taining pollen parietal placentas. masses.
described, but with the ovules on the walls of the cavity (not in its axis or centre), a six-parted perianth, a stamen or stamens and stigmas. The main distinguishing features consist in the fact that one of the inner pieces of the perianth becomes in course of its growth much larger than the rest, and usually different in colour, texture and form. So different is it that it receives a distinct name, that of the "lip" or "labellum." In place of the six stamens we commonly find but one (two in Cypripedium), and that one is raised together with the stigmatic surfaces on an elongation of the floral axis known as the "column." Moreover, the pollen, instead of consisting of separate cells or grains, consists of cells aggregated into "pollen-masses," the number varying in different genera, but very generally two, four, or eight, and in many of the genera provided at the base with a strap-shaped stalk or "caudicle" ending in a flattish gland or "viscid disk" like a boy's sucker. In Cypripedium all three stigmas are functional, but in the great majority of orchids only the lateral pair form receptive surfaces (st, fig. 3), the third being sterile and forming the rostellum which plays an important part in the process of pollination, often forming a peculiar pouch-like process (fig. 4, r) in which the viscid disk of the pollen-masses is concealed till released in the manner presently to be mentioned. It would appear, then, that the orchid flower differs from the more general monocotyledonous type in the irregularity of the perianth, in the suppression of five out of six stamens, and in the union of the one stamen and the stigmas. In addition to these modifications, which are common to nearly all orchids, there are others generally but not so universally met with; among them is the displacement of the flower arising from the twisting of the inferior ovary, in consequence of which the flower is so completely turned round that the "lip," which originates in that part of the flower, conventionally called the posterior or superior part, or that S c ? p-- st--- FIG. I.
A. Floral diagram of typical orchid flower; 1, labellum; a, anther; s, rudiments of barren stamens (staminodes).
B. Diagram of the symmetrical trimerous flower of Fritillary (Fritillaries). FIG. 4. - Diagram illustrating arrangement of parts in flower of Orchis. s, Sepals.
p, Petals.
a, Anther.
st, Two united stigmas. r, Rostellum (barren stigma).
nearest to the supporting stem, becomes in course of growth turned to the anterior or lower part of the flower nearest to the bract, from whose axil it arises. Other common modifications arise from the union of certain parts of the perianth to each other, and from the varied and often very remarkable outgrowths from the lip. These modifications are associated with the structure and habits of insects and their visits to the flowers.
Cross fertilization, or the impregnation of any given flower by pollen from another flower of the same species on the same or on another plant, has been proved to be of great - g advantage to the plant by securing a more FIG. 5. - Pollennumerous or a more robust offspring, or one of anOrchid, better able to adapt itself to the varying masses with their caudicles conditions under which it has to live. This c and common cross fertilization is often effected by the gland g. agency of insects. They are attracted to the flower by its colour or its perfume; they seek, collect or feed on its honey, and while so doing they remove the pollen from the anther and convey it to another flower, there to germinate on the stigma when its tubes travel down the style to the ovary where their contents ultimately fuse with the "oosphere" or immature egg, which becomes in consequence fertilized, and forms a seed which afterwards develops into a new plant (see article Angiosperms). To facilitate the operations of such insects, by compelling them to move in certain lines so as to secure the due removal of the pollen and its subsequent deposit on the right place, the form of the flower and the conformation of its several parts are modified in ways as varied as they are wonderful. Other insects visit the flower with more questionable result. For them the pollen is an attraction as food, or some other part of the flower offers an inducement to them for a like object. Such visitors are clearly prejudicial to the flower, and so we meet with arrangements which are calculated to repel the intruders, or at least to force them to enter the flower in such a way as not to effect mischief. See Darwin's Fertilization of Orchids and similar works.
In the common orchids of British meadows, Orchis Mori-o, mascula (Shakespeare's long purples), &c., the general structure of the flower is as we have described it (figs. 2, 3). In addition there is in this particular genus, as indeed in many others, a long tubular spur or horn projecting downwards from the back of the lip, whose office it is to secrete and store a honeyed juice; the forepart of the lip forms an expanded plate, usually larger and more brightly coloured than the other parts of the flower, and with hairs or ridges and spots of various kinds according to the species. The remaining parts of the perianth are very much smaller, and commonly are so arranged as to form a hood overarching the "column." This column stands up from the base of the flower, almost at right angles to the lip, and it bears at the top an anther, in the two hollow lobes of which are concealed the two pollen-masses, each with its caudicle terminating below in a roundish gland, concealed at first in the pouch-like rostellum at the front of the column. Below the anther the surface of the column in front is hollowed out into a greenish depression covered with viscid fluid - this is the two united stigmas. The other parts of the flower need not detain us. Such being in general terms the mechanism of the flower of a common orchis, let us now see how it acts. A bee, we will assume, attracted by the colour and perfume of the flower, alights on that part of it which is the first to attract its attention - the lip. There, guided by the hairs or ridges before-mentioned, it is led to the orifice of the spur with its store of honeyed juice. The position of this orifice, as we have seen, is at the base of the lip and of the column, so that the insect, if of sufficient size, while bending its head to insert the proboscis into the spur, almost of necessity displaces the pollen-masses. Liberated from the anthers, these adhere to the head or back of the insect by means of the sticky gland at the bottom of the caudicle (fig. 4). Havingattained its object the insect withdraws, taking the pollen-masses, and visits another flower. And now occurs another device or adaptation no less marvellous than those of which mention has been made. The two anther-cases in an orchis are erect and nearly parallel the one to the other; the pollen-masses within them are of course in like case, as may be thus represented II, but immediately the pollen-masses are removed movements take place at the base of the caudicle so as to effect the bending of this stalk and the placing the pollen-mass in a more or less horizontal position, thus -, or, as in the case of 0. pyramidalis, the two pollen-masses originally placed parallel I I diverge from the base like the letter V. The movements of the pollen-masses may readily be seen with the naked eye by thrusting the point of a needle into the base of the anther, when the disks adhere to the needle as they would do to the antenna of an insect, and may be withdrawn. Sometimes the lip is mobile and even sensitive to impressions, as are also certain processes of the column. In such cases the contact of an insect or other body with those processes is sufficient to liberate the pollen often with elastic force, even when the anther itself is not touched. In other orchids movements take place in different ways and in other directions. The object of these movements will be appreciated when it is remembered that, if the pollen-masses retained the original direction they had in the anther in which they were formed, they would, when transported by the insect to another flower, merely come in contact with the anther of that flower, where of course they would be of no use; but, owing to the divergences and flexions above alluded to, the pollen-masses come to be so placed that, when transplanted to another flower of the same species, they come in contact with the stigma and so effect the fertilization of that flower. These illustrations are comparatively simple; it would have been easy to select others of a more complicated nature, but all evidently connected with the visits of insects and the cross fertilization of the flower. In some cases, as in Catasetum, male flowers are produced so different from the female that before the different flowers had been found on the same pike, and before the facts of the case were fully known, they were taken to be representatives of distinct genera.
The fruit is a capsule splitting generally by three longitudinal slits forming valves which remain united above and below. The seeds are minute and innumerable; they contain a small rudimentary embryo surrounded by a thin loose membraneous coat, and are scattered by means of hygroscopic hairs on the inside of the valves which by their movements jerk out the seeds. The floral structure is so curious that perhaps less attention has been paid to the vegetative organs than the peculiarities of their organisation demand. We can only allude to some of these points. The orchids of British fields are all of terrestrial habit, and their roots are mostly tuberous (fig. 6), the tubers being partly radical partly budlike in their character. There is often a marked alternation in the production of vegetative and flowering shoots respectively; and, sometimes, from various circumstances, the flowering shoots are not produced for several years in succession. This fact will account for the profusion with which some orchids, like the common bee orchis for instance, are found in some seasons and their scarcity in others. Tropical orchids are mostly epiphytal - that is, they grow upon trees without deriving nourishment from them. They are frequently provided with "pseudo-bulbs," large solid swellings of the stem, in the tissues of which water and nutritive materials are stored. They derive this moisture from the air by means of aerial roots, developed from the stem and bearing an outer spongy structure, or velamen, consisting of empty cells kept open by spiral thickenings in the wall; this sponge-like tissue absorbs dew and rain and condenses the moisture of the air and passes it on to the internal tissues.
FIG. 6. - Tubercular roots of Orchis mascula, a terrestrial Orchid.
The number of species of orchids is greater than that of any other monocotyledonous order - not even excepting grasses - amounting to 6000, contained in 400 genera. This large number is partly accounted for by the diligent search in all countries that has been made for these plants for purposes of cultivation - they being held at present in the greatest esteem by plantlovers, and prices being paid for new or rare varieties which recall the days of the tulipomania.
The economic uses of orchids are not remarkable. When we have mentioned vanilla, which consists of the fleshy pods of an orchid, we have mentioned about the only economic product that now comes into market. Salep, still used in the Levant, consists of the dried tubers of a terrestrial orchid, and contains a relatively large amount of nutritious matter. The cultivation of orchids is treated under Horticulture.
The order is divided into two main groups based on the number of the stamens and stigmas. The first Diandreae, has two or rarely three fertile stamens and three functional stigmas. It contains two small genera of tropical Asia and Africa with almost regular flowers, and the large genus Cypripedium containing about 80 species in the north-temperate zone and tropical Asia and America. In Cypripedium two stamens are present, one on each side of the column instead of one only at the top, as in the group Monandreae, to which belong the remaining genera in which also only two stigmas are fertile. What may be considered the normal number of stamens is, as has been said, six, arranged in two rows. In most orchids the only stamen developed to maturity is the posterior one of the three opposite to the lip (anterior before the twisting of the ovary), the other two, as well as all three inner ones, being entirely absent, or present only in the form of rudiments. In Cypripedium two of the outer stamens are wanting; the third - the one, that is, which corresponds to the single fertile stamen in the Monandreae - forms a large sterile structure or staminode; the two lateral ones of the inner series are present, the third being undeveloped. This arrangement may be understood by reference to the following diagram, representing the relative position of the stamens in orchids generally and in Cypripedium. The letter L indicates the position of the labellum; the large figures indicate the developed stamens; the italic figures show the position of the suppressed stamens.
I 4 5 6 2 L 3 2 L 3 Arrangement of stamens Arrangement of stamens in Orchis. in Cypripedium. The Monandreae have been subdivided into twenty-eight tribes, the characters of which are based on the structure of the anther and pollinia, the nature of the inflorescence, whether terminal or lateral, the vernation of the leaf and the presence or absence of a joint between blade and sheath, and the nature of the stem. The most important are the following: Ophrydineae, with about 45 genera, of terrestrial orchids, mainly north temperate, including the British genera Orchis, Aceras, Ophrys, Herminium, Gymnadenia and Habenaria. Also some genera mainly represented in South and tropical Africa, such as Satyrium, Disa and others.
Neottiineae, including 90 genera, also terrestrial, contains thirteen more or less widely distributed tropical or subtropical subtribes, some of which extend into temperate zones; one, Cephalanthereae, which includes our British genera Cephalanthera and Epipactis is chiefly north temperate. The British genera Spiranthes, Listera and Neottia are also included in this tribe, as is also Vanilla, the elongated stem of which climbs by means of tendril-like aerial roots - the long fleshy pod is the vanilla used for flavouring.
Coelogyninae, 7 genera, mostly epiphytes, and inhabitants of tropical Asia. A single internode of each shoot is swollen to form a pseudobulb.
Liparidinae, 9 genera, terrestrial, two, Malaxis and Corallorhiza, are British. Liparis is a large genus widely distributed in the tropics.
Pleurothallidinae, characterized by a thin stem bearing one leaf which separates at a distinct joint; the sepals are usually much larger than the petals and lip. Includes To genera, natives of tropical America, one of which, Pleurothallis, contains about 400 species. Masderallia is common in cultivation and has often brilliant scarlet, crimson or orange flowers.
Laeliinae, with 22 genera, natives of the warmer parts of America, including three of those best known in cultivation, Epidendrum, Cattleya and Laelia. The jointed leaves are fleshy or leathery; the flowers are generally large with a well-developed lip.
Phajinae, includes 15 genera chiefly tropical Asiatic, some- Phajus and Calanthe - spreading northwards into China and Japan.
Cystopodiinae, includes 9 genera tropical, but extending into north temperate Asia and South Africa; Eulophia and Lissochilus 'are ' important African genera.
Catasetinae, with three tropical American genera, two of which, Cataselurn and Cycnoches, have dior tri-morphic flowers. They are cultivated for their strange-looking flowers.
Dendrobiinae, with six genera in the warmer parts of the Old World; the chief is Dendrobium, with 300 species, often with showy flowers.
Cymbidiinae, with 8 genera in the tropics of the Old World. The leaves are generally long and narrow. Cymbidium is well known in cultivation.
Oncidiinae, with 44 genera in the warmer parts of America. Odontoglossum and Oncidium include some of the best-known cultivated orchids.
Sarcanthinae, with 42 genera in the tropics. Vanda (Asia) and Angraecum (Africa and Madagascar) are known in cultivation. The flower of Angraecum sesquipedale has a spur 18 in. in length.
The order is well represented in Britain by 18 genera, which include several species of Orchis: Gymnadenia (fragrant orchis), Habenaria (butterfly and frog orchis), Aceras (man orchis), Hermin- ium (musk orchis), Ophrys (bee, spider and fly orchis), Epipactis (Helleborine), Cephalanthera, Neottia (bird's-nest orchis), one of the few saprophytic genera, which have no green leaves, but derive their nourishment from decaying organic matter in the soil, Listens (Tway blade), Spiranthes (lady's tresses), Malaxis (bog-orchis), Liparis (fen-orchis), Corallorhiza (coral root), also a saprophyte, and Cypripedium (lady's slipper), represented by a single species now very rare in limestone districts in the north of England.
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