Angraecum sesquipedale
Encyclopedia
Angraecum sesquipedale (also called Darwin's orchid, Christmas orchid, Star of Bethlehem orchid, and King of the Angraecums) is an epiphytic orchid in the genus Angraecum
that is endemic to Madagascar
. The orchid was first discovered by the French botanist Louis-Marie Aubert du Petit-Thouars
in 1798, but was not described until 1822. It is noteworthy for its long spur and its association with the naturalist Charles Darwin
who surmised that the flower was pollinated by a then undiscovered moth with a proboscis whose length was then unprecedented. His prediction had gone unverified until 21 years after his death when the moth was discovered and his conjecture vindicated. The story of its postulated pollinator has come to be seen as one of the celebrated predictions of the theory of evolution
.
growth and can get to a height of 1 metres (3.3 ft). Its growth habit is rather similar to species in the genus Aerides
.
The leaves are dark green with a bit of a grayish tone and leathery with a bilobed tip. They are usually around 20 – long and 6 – wide. The roots are dark gray, thick, and emerge from the orchid's stem. There tends to be few roots and they attach to the bark of the trees quite strongly. Each of the succulent roots can extend along the trunk of the tree for several meters.
There is also a variations of this species namely A. sesquipedale var. angustifolium. A. sesquipedale var. angustifolium tends to be smaller than A. sesquipedale and has narrower leaves. The chromosome number
of A. sesquipedale is 2n=42. A. sesquipedale has also previously gone by the synonyms
Aeranthes sesquipedalis Lindl. (1824), Macroplectrum sesquipedale Pfitzer (1889), Angorchis sesquepedalis Kuntze (1891), and Mystacidium sesquipedale Rolfe (1904).
at altitudes below 400–500 ft, near the east coast of the island, and on trees that are at the edge of forests. Usually it is attached to trees with fewer leaves and to areas of the branch or trunk that are driest. This allows the plant to obtain a great deal of light and air movement. Larger plants are usually found growing within 12–20 ft from the ground, whereas smaller plants are often found higher up in the canopy. Rarely A. sesquipedale is also found growing as a lithophyte
and sometimes even as a semi-terrestrial. The orchid lives in an environment with heavy rainfall, up to 150 in (381 cm) per year. There is no dry season
so the growing season
is continuous.
Star-like waxy flowers are produced on 30 cm (11.8 in) inflorescences arising from the stem from June to September in the wild with most flowers wilting by August. When cultivated in Europe
however, the plant flowers between December and January. This flowering habit is what lends the orchid several of its common name
s, such as "Comet orchid" due to the shape of its flower and "Christmas orchid" due to the timing of its flowering. Each flower opens up with a green color, but eventually turns white with tones of light green. The amount of green in each flower can vary from plant to plant. It is claimed that the age-dependent color change is more pronounced in wild A. sesquipedale than in greenhouse-grown plants. The sepal
s tend to stay green for a longer time than the petals. As the flower ages further it goes from white to yellowish and then from orange to brown as it begins to wilt. As the wilting progresses the dorsal sepal bends down and then the lateral sepals bend inward with the lip remaining fairly stationary. Finally the entire flower closes in on itself. A distinctive feature of the flowers is that they have a long green spur
attached. The spur of the flower is 27 – from its tip to the tip of the flower's lip. The specific epithet sesquipedale is Latin
for "one-and-a-half-feet-long," referring to the distance between the end of the spur and the very top of the dorsal sepal. At the end of the spur is a small amount of nectar usually about 40–300 µl in volume. In general, longer spurs tend to have greater concentrations of nectar. This nectar fills the spur up to within 7 to 25 cm (2.8 to 9.8 in) from the bottom of the spur. The nectar has been found to contain the sugars fructose
, sucrose
, glucose
, and raffinose
. The flowers produce an extremely intense spicy scent that can easily fill a room; this fragrance is only present during the night and is reminiscent of lily and some nocturnally flowering Nicotiana
species. The scent has been found to be composed of approximately 39 different chemical constituents with its greatest concentration consisting of isovaleraldoxime, methyl benzoate
, benzyl alcohol
, isovaleronitrile, benzyl benzoate
, phenylethyl alcohol, isovaleraldehyde, and phenylacetaldoxime. Usually 1 to 5 flowers are produced at a time.
community, especially for its association with the naturalist Charles Darwin. After being sent several flowers of A. sesquipedale by James Bateman
, Darwin noted the defining characteristic of the species, its extremely long spur. From his observations, Darwin surmised, in his 1862 publication On the various contrivances by which British and foreign orchids are fertilized by insects, and on the good effects of intercrossing
, that there must be a pollinator moth with a proboscis
long enough to reach the nectar at the end of the spur. He arrived at this conclusion after attempting in vain to remove the pollinia of the flower using needles and bristles. Only after placing a cylinder with a diameter of of an inch down the full length of the spur was he able to detach the pollinia upon retracting it. The viscidium attached to the cylinder as he removed it. Darwin surmised that in the moth's attempt at getting the nectar at the end of the spur the moth would get the pollinarium attached to itself. The next orchid it visited would then be pollinated in the same manner. For some time after this prediction the notion of a pollinator with a 35 cm long proboscis
was ridiculed and generally not believed to exist. After Darwin's publication, George Campbell
published a book in 1867 titled, The Reign of Law, in which he attempted to argue that the complexity of this species implied that it was created by a supernatural being. However, in 1903, such a moth was discovered in Madagascar by Lionel Walter Rothschild and Karl Jordan
. This confirmed Darwin's prediction. The moth was named Xanthopan morganii praedicta
. The subspecific epithet praedicta was given in honor of the fact that Darwin predicted its existence, though the subspecies
was later determined to be invalid (it is identical to the mainland form of the species).
In 1873 W. A. Forbes wrote an article in the journal Nature asking readers if they knew of the moth predicted by Darwin. A reply to the question was first made that same year by Hermann Müller
. He announced that his brother Fritz Müller
had discovered a moth with a proboscis of 30 – long, but it was discovered in Brazil
and so was not a candidate for pollinating A. sesquipedale. Although Darwin learned of Müller's finding he did not live to see the discovery of Xanthopan morgani. Even after the 1903 discovery however, news of Xanthopan morganii praedicta didn't immediately disseminate. A second inquiry into the existence of the pollinator moth was made in the January 30, 1907 issue of the journal Nature by E. W. Swanton. Presumably still unaware of Rothschild and Jordan's discovery, Alfred Russel Wallace
responded stating that he didn't know of a suitable pollinator in Madagascar, but that he had heard of one from East Africa with a long enough proboscis.
Both Darwin and Alfred Russel Wallace had suggested that the evolutionary basis for how the odd relationship between the sphinx moth and A. sesquipedale evolved over time could be understood by considering one orchid with a long spur and another with a short spur. If a moth goes to fertilize a flower with a short spur its proboscis would easily reach all the way to the bottom of the spur and it would get the nectar. However, since the proboscis of the moth is longer than the spur of the flower; the head of the moth would not touch the flower obtaining the pollinarium and so the flower would not be fertilized. The orchid with the longer spur on the other hand would be able to be fertilized since the entire length of the proboscis fits within the spur and thus allowing the head of the moth to touch the flower and become connected to the pollinarium. As a result, over time plants with longer spurs would be more likely to reproduce and so become more prevalent in the population. In this way A. sesquipedale has evolved to have a very long spur. The moth too would evolve to have a longer and longer proboscis in the following way. If a moth goes to fertilize an A. sesquipedale flower and the spur is longer than its proboscis then it will not be able to reach all of the nectar. As such, moths with too short of a proboscis would not be able to get as much food as those moths with a longer proboscis who could reach all of the nectar. Due to this arrangement moths with longer proboscis would become more physically fit to reproduce due to their ability to get more nectar and so such moths would become more prevalent in the population. This can result in a seasawing effect by which both organisms produce a mechanism that leads the other to increase the others spur and proboscis. There are however certain properties that no doubt prevent this mechanism from continuing indefinitely. For example, the risk such a long proboscis poses to a moth could be a factor that would prevent the spur of A. sesquipedale from becoming indefinitely long. If moths with proboscises that were too long substantially risked their lives due to being easier prey, then such moths could only afford to evolve a proboscis to a certain length. This would in turn restrict the length of the orchid's spur, since moths would not want to visit flowers whose spurs were too long since they would not be able to reach the nectar.
There was also another explanation for why the spur of A. sesquipedale grew so long proposed by Thomas Belt
in his 1874 book The Naturalist in Nicaragua. Belt suggested that the spur grew long in order to prevent other moths with shorter proboscises from drinking the nectar. Darwin took up this explanation briefly in a footnote of the second edition of his famous orchid book, explaining that although this explanation was no doubt true, it cannot account for the lengthening spur.
The fertilization of A. sesquipedale has been observed to proceed as follows. The moth approaches the flower to ascertain by scent whether or not it is the correct orchid species. Then the moth backs up over a foot and unrolls its proboscis, then flies forward, inserting it into a cleft in the rostellum which leads to the spur while gripping the labellum. After the moth has finished drinking the nectar, which usually takes about 6 seconds, it instinctively raises its head while removing its proboscis from the spur, and in doing so causes the viscidium to adhere to its proboscis usually about 4 to 9 mm (0.15748031496063 to 0.354330708661417 in) from its base. Attached to the viscidium via the caudicle
is the pollinia. Upon removing its proboscis from the flower, the pollinarium stalk will be straight and parallel with the moth's proboscis. Then after leaving the orchid the caudicle will eventually dry out, causing its angle relative to the moth's proboscis to change by 90° so that it is at the correct angle to attach to the stigma
of the next orchid the moth visits. The moth then repeats this process at another A. sesquipedale orchid and simultaneously fertilizes it. Once the flower has been fertilized, it quickly stops producing its powerful scent.
could have evolved long proboscises as a predatory avoidance strategy from heteropodid spiders. Since such spiders have been known to jump at hovering moths in an attempt at eating them, hawk moths would be at risk when visiting flowers if such a spider was nearby. Based on this reasoning moths with longer tongues would be less at risk when pollinating flowers since they would be farther away and thus a more challenging target for jumping spider
s. As a result nature would select for hawk moths with longer and longer proboscis. The flowers of A. sesquipedale on the other hand would be evolving longer spurs since flowers with longer spurs are more likely to become fertilized by long tongued moths. In other words, the flowers evolve long spurs to fit the pollinators and not the reverse. It has also been observed that the moths will swing side to side when feeding, presumably to evade jumping spiders. Possible problems with this hypothesis is that active predation by spiders on hawk moths visiting flowers has not been observed. It has also been suggested that flying predators such as bats and birds are the more likely predators to hawk moths. Whether or not the pollinator shift model or the coevolution model, or even a little bit of both are correct is currently the subject of debate.
of the Angraecoid species. The following is a portion of the resultant Bayesian tree they obtained, showing part of clade 2.
The cladogram indicates that A. cucullatum is the most closely related species to A. sesquipedale.
Angraceum sesquipedale was first brought to the United Kingdom
in 1855 to be grown outside of its natural environment by William Ellis. Subsequently, Ellis achieved the first flowering of the plant in cultivation in 1857. Angraecum sesquipedale has been attributed as having a nicer appearance when grown in cultivation than when found in the wild, since wild specimens appear as a long stem surrounded by a few struggling leaves. Additionally, A. sesquipedale is seldom grown in private collections, despite its enormous importance to Darwin's concept of co-evolution
and subsequently the fields of botany
and evolutionary biology.
It's often recommended that A. sesquipedale be grown under warm to intermediate conditions and given as much light as possible without burning the leaves. The choice of growing the plant in intermediate or warm housing conditions can affect the timing of the flowering. In order to stimulate heavy flower production its important that the light intensity be greatest between September and November. The number of flower spikes present during flowering is dependent on the number of new leaf-pairs formed during the preceding spring and summer, since each newly formed leaf-pair produce one spike and rarely two. Angraecum sesquipedale is commonly found to have a slow growth habit, but the orchid can be expected to produce flowers even before it has reached an adult size. Angraecum sesquipedale is notorious for having sensitive roots. The roots of mature plants are best left undisturbed as much as possible and as a result its prudent to be especially careful during repotting. Young plants however are less susceptible to such root problems. Disturbing the roots can cause the plant to sulk for 2 to 4 years or even to cause it to die. When a mature plant is disturbed it frequently looses many of its lower leaves and reverts to only producing one or two flowers at a time. To avoid these problems its commonly advised that the orchid be planted in a coarse medium such as fir bark, crock, or charcoal to minimize disturbances to the roots. Also planting it in a basket or large pot is best since this allows the orchid to grow for many years before having to have its roots disturbed.
, an employee of Veitch Nurseries
, and exhibited for the first time on January 10, 1899. It was named A. Veitchii, but it also commonly goes by the name King of the Angraceum hybrids. The cross was between A. sesquipedale and A. eburneum. The flowers somewhat resemble those of A. leonis
. Another common cross involving A. sesquipedale is A. Crestwood, which is a cross between A. Veitchii and A. sesquipedale.
Angraecum
The genus Angraecum, abbreviated as Angcm in horticultural trade, common name Angrek or Comet Orchid, contains about 220 species, some of them among most magnificent of all orchids. They are quite varied vegetatively and florally and are adapted to dry tropical woodland habitat and have quite...
that is endemic to Madagascar
Madagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...
. The orchid was first discovered by the French botanist Louis-Marie Aubert du Petit-Thouars
Louis-Marie Aubert du Petit-Thouars
Louis-Marie Aubert du Petit-Thouars was an eminent French botanist.-Introduction:He was from an aristocrat family of the region of Anjou, where he grew up in the castle of Boumois, near Saumur...
in 1798, but was not described until 1822. It is noteworthy for its long spur and its association with the naturalist Charles Darwin
Charles Darwin
Charles Robert Darwin FRS was an English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection.He published his theory...
who surmised that the flower was pollinated by a then undiscovered moth with a proboscis whose length was then unprecedented. His prediction had gone unverified until 21 years after his death when the moth was discovered and his conjecture vindicated. The story of its postulated pollinator has come to be seen as one of the celebrated predictions of the theory of evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
.
Description
Angraecum sesquipedale is a monocot with monopodialMonopodial
Vascular plants with monopodial growth habits grow upward from a single point. They add leaves to the apex each year and the stem grows longer accordingly...
growth and can get to a height of 1 metres (3.3 ft). Its growth habit is rather similar to species in the genus Aerides
Aerides
Aerides also known as the Cat's-tail Orchid or the Fox Brush Orchid, is a genus belonging to the Orchid family . It is a group of tropical epiphyte orchids that grow mainly in the warm low-lands of the tropics of Asia...
.
There is also a variations of this species namely A. sesquipedale var. angustifolium. A. sesquipedale var. angustifolium tends to be smaller than A. sesquipedale and has narrower leaves. The chromosome number
Ploidy
Ploidy is the number of sets of chromosomes in a biological cell.Human sex cells have one complete set of chromosomes from the male or female parent. Sex cells, also called gametes, combine to produce somatic cells. Somatic cells, therefore, have twice as many chromosomes. The haploid number is...
of A. sesquipedale is 2n=42. A. sesquipedale has also previously gone by the synonyms
Synonym (taxonomy)
In scientific nomenclature, a synonym is a scientific name that is or was used for a taxon of organisms that also goes by a different scientific name. For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies...
Aeranthes sesquipedalis Lindl. (1824), Macroplectrum sesquipedale Pfitzer (1889), Angorchis sesquepedalis Kuntze (1891), and Mystacidium sesquipedale Rolfe (1904).
Habitat
It is often found in lowlands in MadagascarMadagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...
at altitudes below 400–500 ft, near the east coast of the island, and on trees that are at the edge of forests. Usually it is attached to trees with fewer leaves and to areas of the branch or trunk that are driest. This allows the plant to obtain a great deal of light and air movement. Larger plants are usually found growing within 12–20 ft from the ground, whereas smaller plants are often found higher up in the canopy. Rarely A. sesquipedale is also found growing as a lithophyte
Lithophyte
Lithophytes are a type of plant that grows in or on rocks. Lithophytes feed off moss, nutrients in rain water, litter, and even their own dead tissue....
and sometimes even as a semi-terrestrial. The orchid lives in an environment with heavy rainfall, up to 150 in (381 cm) per year. There is no dry season
Dry season
The dry season is a term commonly used when describing the weather in the tropics. The weather in the tropics is dominated by the tropical rain belt, which oscillates from the northern to the southern tropics over the course of the year...
so the growing season
Growing season
In botany, horticulture, and agriculture the growing season is the period of each year when native plants and ornamental plants grow; and when crops can be grown....
is continuous.
Flower
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
however, the plant flowers between December and January. This flowering habit is what lends the orchid several of its common name
Common name
A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...
s, such as "Comet orchid" due to the shape of its flower and "Christmas orchid" due to the timing of its flowering. Each flower opens up with a green color, but eventually turns white with tones of light green. The amount of green in each flower can vary from plant to plant. It is claimed that the age-dependent color change is more pronounced in wild A. sesquipedale than in greenhouse-grown plants. The sepal
Sepal
A sepal is a part of the flower of angiosperms . Collectively the sepals form the calyx, which is the outermost whorl of parts that form a flower. Usually green, sepals have the typical function of protecting the petals when the flower is in bud...
s tend to stay green for a longer time than the petals. As the flower ages further it goes from white to yellowish and then from orange to brown as it begins to wilt. As the wilting progresses the dorsal sepal bends down and then the lateral sepals bend inward with the lip remaining fairly stationary. Finally the entire flower closes in on itself. A distinctive feature of the flowers is that they have a long green spur
Spur (biology)
A spur in botany is a spike, usually part of a flower.In certain plants, part of a sepal or petal develops into an elongated hollow spike extending behind the flower, containing nectar which is sucked by long-tongued animals . Plants with such structures include Delphinium, Aquilegia, Piperia, and...
attached. The spur of the flower is 27 – from its tip to the tip of the flower's lip. The specific epithet sesquipedale is Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
for "one-and-a-half-feet-long," referring to the distance between the end of the spur and the very top of the dorsal sepal. At the end of the spur is a small amount of nectar usually about 40–300 µl in volume. In general, longer spurs tend to have greater concentrations of nectar. This nectar fills the spur up to within 7 to 25 cm (2.8 to 9.8 in) from the bottom of the spur. The nectar has been found to contain the sugars fructose
Fructose
Fructose, or fruit sugar, is a simple monosaccharide found in many plants. It is one of the three dietary monosaccharides, along with glucose and galactose, that are absorbed directly into the bloodstream during digestion. Fructose was discovered by French chemist Augustin-Pierre Dubrunfaut in 1847...
, sucrose
Sucrose
Sucrose is the organic compound commonly known as table sugar and sometimes called saccharose. A white, odorless, crystalline powder with a sweet taste, it is best known for its role in human nutrition. The molecule is a disaccharide composed of glucose and fructose with the molecular formula...
, glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
, and raffinose
Raffinose
Raffinose is a trisaccharide composed of galactose, fructose, and glucose. It can be found in beans, cabbage, brussels sprouts, broccoli, asparagus, other vegetables, and whole grains. Raffinose can be hydrolyzed to D-galactose and sucrose by the enzyme α-galactosidase , an enzyme not found in the...
. The flowers produce an extremely intense spicy scent that can easily fill a room; this fragrance is only present during the night and is reminiscent of lily and some nocturnally flowering Nicotiana
Nicotiana
Nicotiana is a genus of herbs and shrubs of the nightshade family indigenous to North and South America, Australia, south west Africa and the South Pacific. Various Nicotiana species, commonly referred to as tobacco plants, are cultivated and grown to produce tobacco. Of all Nicotiana species,...
species. The scent has been found to be composed of approximately 39 different chemical constituents with its greatest concentration consisting of isovaleraldoxime, methyl benzoate
Methyl benzoate
Methyl benzoate is an ester with the chemical formula C6H5COOCH3. It is formed by the condensation of methanol and benzoic acid, in presence of a strong acid such as hydrochloric acid. It is a colorless liquid that is poorly soluble in water, but miscible with organic solvents.-Reactions:Methyl...
, benzyl alcohol
Benzyl alcohol
Benzyl alcohol is an organic compound with the formula C6H5CH2OH. The benzyl group is often abbreviated "Bn", thus benzyl alcohol is denoted as BnOH. Benzyl alcohol is a colorless liquid with a mild pleasant aromatic odor. It is a useful solvent due to its polarity, low toxicity, and low vapor...
, isovaleronitrile, benzyl benzoate
Benzyl benzoate
Benzyl benzoate is the ester of benzyl alcohol and benzoic acid, with the formula C6H5CH2O2CC6H5. This easily prepared compound has a variety of uses.-Synthesis:This colorless liquid is formally the condensation product of benzoic acid and benzyl alcohol...
, phenylethyl alcohol, isovaleraldehyde, and phenylacetaldoxime. Usually 1 to 5 flowers are produced at a time.
Coevolution model
This orchid is well-known within the botanyBotany
Botany, plant science, or plant biology is a branch of biology that involves the scientific study of plant life. Traditionally, botany also included the study of fungi, algae and viruses...
community, especially for its association with the naturalist Charles Darwin. After being sent several flowers of A. sesquipedale by James Bateman
James Bateman
James Bateman was a landowner and accomplished horticulturist. He developed Biddulph Grange after moving there around 1840, from nearby Knypersley Hall...
, Darwin noted the defining characteristic of the species, its extremely long spur. From his observations, Darwin surmised, in his 1862 publication On the various contrivances by which British and foreign orchids are fertilized by insects, and on the good effects of intercrossing
Fertilisation of Orchids
Fertilisation of Orchids is a book by Charles Darwin published on 15 May 1862 under the full explanatory title On the various contrivances by which British and foreign orchids are fertilised by insects, and on the good effects of intercrossing...
, that there must be a pollinator moth with a proboscis
Proboscis
A proboscis is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In simpler terms, a proboscis is the straw-like mouth found in several varieties of species.-Etymology:...
long enough to reach the nectar at the end of the spur. He arrived at this conclusion after attempting in vain to remove the pollinia of the flower using needles and bristles. Only after placing a cylinder with a diameter of of an inch down the full length of the spur was he able to detach the pollinia upon retracting it. The viscidium attached to the cylinder as he removed it. Darwin surmised that in the moth's attempt at getting the nectar at the end of the spur the moth would get the pollinarium attached to itself. The next orchid it visited would then be pollinated in the same manner. For some time after this prediction the notion of a pollinator with a 35 cm long proboscis
Proboscis
A proboscis is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In simpler terms, a proboscis is the straw-like mouth found in several varieties of species.-Etymology:...
was ridiculed and generally not believed to exist. After Darwin's publication, George Campbell
George Campbell, 8th Duke of Argyll
George John Douglas Campbell, 8th Duke of Argyll KG, KT, PC, FRS, FRSE , styled Marquess of Lorne until 1847, was a Scottish peer, Liberal politician as well as a writer on science, religion, and the politics of the 19th century.-Background:Argyll was born at Ardencaple Castle, Dunbartonshire, the...
published a book in 1867 titled, The Reign of Law, in which he attempted to argue that the complexity of this species implied that it was created by a supernatural being. However, in 1903, such a moth was discovered in Madagascar by Lionel Walter Rothschild and Karl Jordan
Karl Jordan
Heinrich Ernst Karl Jordan was a German entomologist.Jordan was born in Hanover and educated at Göttingen University. In 1893 he began work at the Walter Rothschild's Museum at Tring, specialising in Coleoptera, Lepidoptera and Siphonaptera...
. This confirmed Darwin's prediction. The moth was named Xanthopan morganii praedicta
Xanthopan morgani
Xanthopan morgani, or Morgan's Sphinx, is a very large hawk moth from West Africa and Madagascar. It is the sole member of its genus, and little is known of the biology, though the adults have been found to visit orchids .In January 1862 while researching insect pollination of orchids, Charles...
. The subspecific epithet praedicta was given in honor of the fact that Darwin predicted its existence, though the subspecies
Subspecies
Subspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one...
was later determined to be invalid (it is identical to the mainland form of the species).
Hermann Müller (botanist)
Heinrich Ludwig Hermann Müller , German botanist who provided important evidence for Darwin's theory of evolution. He was the author in 1873 of Die Befruchtung der Blumen durch Insekten, a book translated at the suggestion of Darwin in 1883 as The fertilisation of flowers...
. He announced that his brother Fritz Müller
Fritz Müller
Johann Friedrich Theodor Müller , better known as Fritz Müller, and also as Müller-Desterro, was a German biologist and physician who emigrated to southern Brazil, where he lived in and near the German community of Blumenau, Santa Catarina...
had discovered a moth with a proboscis of 30 – long, but it was discovered in Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
and so was not a candidate for pollinating A. sesquipedale. Although Darwin learned of Müller's finding he did not live to see the discovery of Xanthopan morgani. Even after the 1903 discovery however, news of Xanthopan morganii praedicta didn't immediately disseminate. A second inquiry into the existence of the pollinator moth was made in the January 30, 1907 issue of the journal Nature by E. W. Swanton. Presumably still unaware of Rothschild and Jordan's discovery, Alfred Russel Wallace
Alfred Russel Wallace
Alfred Russel Wallace, OM, FRS was a British naturalist, explorer, geographer, anthropologist and biologist...
responded stating that he didn't know of a suitable pollinator in Madagascar, but that he had heard of one from East Africa with a long enough proboscis.
Both Darwin and Alfred Russel Wallace had suggested that the evolutionary basis for how the odd relationship between the sphinx moth and A. sesquipedale evolved over time could be understood by considering one orchid with a long spur and another with a short spur. If a moth goes to fertilize a flower with a short spur its proboscis would easily reach all the way to the bottom of the spur and it would get the nectar. However, since the proboscis of the moth is longer than the spur of the flower; the head of the moth would not touch the flower obtaining the pollinarium and so the flower would not be fertilized. The orchid with the longer spur on the other hand would be able to be fertilized since the entire length of the proboscis fits within the spur and thus allowing the head of the moth to touch the flower and become connected to the pollinarium. As a result, over time plants with longer spurs would be more likely to reproduce and so become more prevalent in the population. In this way A. sesquipedale has evolved to have a very long spur. The moth too would evolve to have a longer and longer proboscis in the following way. If a moth goes to fertilize an A. sesquipedale flower and the spur is longer than its proboscis then it will not be able to reach all of the nectar. As such, moths with too short of a proboscis would not be able to get as much food as those moths with a longer proboscis who could reach all of the nectar. Due to this arrangement moths with longer proboscis would become more physically fit to reproduce due to their ability to get more nectar and so such moths would become more prevalent in the population. This can result in a seasawing effect by which both organisms produce a mechanism that leads the other to increase the others spur and proboscis. There are however certain properties that no doubt prevent this mechanism from continuing indefinitely. For example, the risk such a long proboscis poses to a moth could be a factor that would prevent the spur of A. sesquipedale from becoming indefinitely long. If moths with proboscises that were too long substantially risked their lives due to being easier prey, then such moths could only afford to evolve a proboscis to a certain length. This would in turn restrict the length of the orchid's spur, since moths would not want to visit flowers whose spurs were too long since they would not be able to reach the nectar.
There was also another explanation for why the spur of A. sesquipedale grew so long proposed by Thomas Belt
Thomas Belt
Thomas Belt , an English geologist and naturalist, was born at Newcastle-on-Tyne in 1832, and educated in that city. He is remembered for his work on the geology of gold bearing minerals, glacial geology, and for his description of the mutualistic relationship between certain bullthorn Acacia...
in his 1874 book The Naturalist in Nicaragua. Belt suggested that the spur grew long in order to prevent other moths with shorter proboscises from drinking the nectar. Darwin took up this explanation briefly in a footnote of the second edition of his famous orchid book, explaining that although this explanation was no doubt true, it cannot account for the lengthening spur.
Stipe (botany)
In botany, a stipe is a stalk that supports some other structure. The precise meaning is different depending on which taxonomic group is being described....
is the pollinia. Upon removing its proboscis from the flower, the pollinarium stalk will be straight and parallel with the moth's proboscis. Then after leaving the orchid the caudicle will eventually dry out, causing its angle relative to the moth's proboscis to change by 90° so that it is at the correct angle to attach to the stigma
Gynoecium
Gynoecium is most commonly used as a collective term for all carpels in a flower. A carpel is the ovule and seed producing reproductive organ in flowering plants. Carpels are derived from ovule-bearing leaves which evolved to form a closed structure containing the ovules...
of the next orchid the moth visits. The moth then repeats this process at another A. sesquipedale orchid and simultaneously fertilizes it. Once the flower has been fertilized, it quickly stops producing its powerful scent.
Pollinator shift model
An alternative path by which A. sesquipedale could have evolved that differed with Darwin and Wallace's explanation was proposed by Lutz Thilo Wasserthal in 1997. According to Wasserthal, hawk mothsSphingidae
Sphingidae is a family of moths , commonly known as hawk moths, sphinx moths and hornworms, that includes about 1,200 species . It is best represented in the tropics but there are species in every region . They are moderate to large in size and are distinguished among moths for their rapid,...
could have evolved long proboscises as a predatory avoidance strategy from heteropodid spiders. Since such spiders have been known to jump at hovering moths in an attempt at eating them, hawk moths would be at risk when visiting flowers if such a spider was nearby. Based on this reasoning moths with longer tongues would be less at risk when pollinating flowers since they would be farther away and thus a more challenging target for jumping spider
Jumping spider
The jumping spider family contains more than 500 described genera and about 5,000 described species, making it the largest family of spiders with about 13% of all species. Jumping spiders have some of the best vision among invertebrates and use it in courtship, hunting and navigation...
s. As a result nature would select for hawk moths with longer and longer proboscis. The flowers of A. sesquipedale on the other hand would be evolving longer spurs since flowers with longer spurs are more likely to become fertilized by long tongued moths. In other words, the flowers evolve long spurs to fit the pollinators and not the reverse. It has also been observed that the moths will swing side to side when feeding, presumably to evade jumping spiders. Possible problems with this hypothesis is that active predation by spiders on hawk moths visiting flowers has not been observed. It has also been suggested that flying predators such as bats and birds are the more likely predators to hawk moths. Whether or not the pollinator shift model or the coevolution model, or even a little bit of both are correct is currently the subject of debate.
Related species
In 2008, Micheneau et al. performed a cladistic analysisCladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
of the Angraecoid species. The following is a portion of the resultant Bayesian tree they obtained, showing part of clade 2.
The cladogram indicates that A. cucullatum is the most closely related species to A. sesquipedale.
Cultivation
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
in 1855 to be grown outside of its natural environment by William Ellis. Subsequently, Ellis achieved the first flowering of the plant in cultivation in 1857. Angraecum sesquipedale has been attributed as having a nicer appearance when grown in cultivation than when found in the wild, since wild specimens appear as a long stem surrounded by a few struggling leaves. Additionally, A. sesquipedale is seldom grown in private collections, despite its enormous importance to Darwin's concept of co-evolution
Co-evolution
In biology, coevolution is "the change of a biological object triggered by the change of a related object." Coevolution can occur at many biological levels: it can be as microscopic as correlated mutations between amino acids in a protein, or as macroscopic as covarying traits between different...
and subsequently the fields of botany
Botany
Botany, plant science, or plant biology is a branch of biology that involves the scientific study of plant life. Traditionally, botany also included the study of fungi, algae and viruses...
and evolutionary biology.
Hybrids
The first Angraecum hybrid was created by John SedenJohn Seden
John Seden was a famous hybridist and horticulturalist best known for the hybrids he created while in the employment of Veitch nurseries. He was trained in hybridizing by John Dominy in 1861. In 1873 he began hybridizing tuberous begonias which in turn formed the basis from which modern garden...
, an employee of Veitch Nurseries
Veitch Nurseries
The Veitch Nurseries were the largest group of family-run plant nurseries in Europe during the 19th century. Started by John Veitch sometime before 1808, the original nursery grew substantially over several decades and was eventually split into two separate businesses - based at Chelsea and...
, and exhibited for the first time on January 10, 1899. It was named A. Veitchii, but it also commonly goes by the name King of the Angraceum hybrids. The cross was between A. sesquipedale and A. eburneum. The flowers somewhat resemble those of A. leonis
Angraecum leonis
Angraecum leonis is a species of orchid....
. Another common cross involving A. sesquipedale is A. Crestwood, which is a cross between A. Veitchii and A. sesquipedale.
Interspecific hybrids
- Angraecum Appalachian Star (Angraecum sesquipedale x Angraecum praestans)
- Angraecum Crestwood (Angraecum Veitchii x Angraecum sesquipedale)
- Angraecum Dianne's Darling (Angraecum sesquipedale x Angraecum Alabaster)
- Angraecum Lemförde White Beauty (Angraecum magdalenae x Angraecum sesquipedale)
- Angraecum Malagasy (Angraecum sesquipedale x Angraecum sororium)
- Angraecum Memoria Mark Aldridge (Angraecum sesquipedale x Angraecum eburneum subsp. superbum)
- Angraecum North Star (Angraecum sesquipedale x Angraecum leonis)
- Angraecum Ol Tukai (Angraecum comorense x Angraecum sesquipedale)
- Angraecum Orchidglade (Angraecum sesquipedale x Angraecum giryamae)
- Angraecum Rose Ann Carroll (Angraecum eichlerianum x Angraecum sesquipedale)
- Angraecum Sesquibert (Angraecum sesquipedale x Angraecum humbertii)
- Angraecum Sesquivig (Angraecum viguieri x Angraecum sesquipedale)
- Angraecum Star Bright (Angraecum sesquipedale x Angraecum didieri)
- Angraecum Veitchii (Angraecum eburneum x Angraecum sesquipedale)
Intergeneric hybrids
- Angranthes Paille en Queue (Angraecum sesquipedale x Aeranthes arachnites)
- Angranthes Sesquimosa (Aeranthes ramosa x Angraecum sesquipedale)
- Chouara Kaohsiung Dream (Angraecum sesquipedale x Doritaenopsis Ruey Lih Beauty)
- Eurygraecum Lydia (Angraecum sesquipedale x Eurychone rothschildiana)
- Vandaecum Enzomondo Amore (Vanda Rothschildiana x Angraecum sesquipedale)
External links
- Orchids of the World
- Wikimedia Commons: More Pictures of Angraecum Sesquipedale
- Video showing hawk moth pollinating Angraecum Sesquipedale