Orchid

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Orchidaceae
Cypripedium reginae
Cypripedium reginae
Scientific classification
Domain: Eukaryota
Kingdom: Plantae
Division: Magnoliophyta
Class: Liliopsida
Order: Asparagales
Family: Orchidaceae
Juss. 1789
Type genus
Orchis L. 1753
Subfamilies
Synonyms

There are literally tens of thousands of species, cultivars and varieties in the orchid family, the largest family of flowering plants. The word orchid may refer to any of the botanical family Orchidaceae, or, more commonly among lay persons, any of thousands of flowers called "orchids".

Orchids are ancient, and have been cultivated for centuries. They range from rare and recent discoveries such as the tiny Tallong Midge Orchid to the large, showy orchids which are featured in bouquets and corsages, to food orchids such as vanilla. A few orchids have insignificant flowers and are grown for their foliage.

Orchids seemed to be fascinating: every developed nation has many orchid societies, and this fascination extends beyond form and beauty. Because of their biological importance (some orchids have developed extraordinary systems of pollination, for example, "Lady's Slipper" traps insects and so forces them to pollinate the flower; one Australian orchid exists underground and is pollinated by ants; many give off attractive odours), orchids hold just as much interest for scientists. Famed biologist Ernst Mayr discovered and named 38 new species of orchid. [1]

Distribution

Despite their distribution is largely irregular throughout the globe, orchids can be found in almost all regions of the planet, except Antartic continet. Due to their wide greographic distribution, it is natural that a so diverse group of plants show high degree of adaptation to different climates and to the multiplicity of polinators present in each area.[2] The number of orchid genera that exist on every continent is not exact because there is no consensus among the taxonomists about how to split them, however, it can be estimated as follow: Eurasia, about 50 genera; North America, circa 25 genera, Latin America and Caribbean, between 300 and 350; tropical Asia, between 250 and 300; tropical Africa, circa 250; and Oceania, about 60.[3]

The largest diversity of orchid species occurs in tropical areas of the globe, notably on mountain areas, which are natural bareers that insolate the several populations of plants. Islands also favor development of species but unlikely mountain areas, islands do not favor diversity that much because, unless the island is large enough to have a variety of climates, what is more commen is to find a high number of few endemic species that do not exist anywhere else. Exceptions are large islands as Borneo, New Guinea, Madagascar and some other, where the diversity is enormous, these have both a high number of endemisms and wealthy of different species. Therefore, some of the main areas in the world noted for having a large number of species are the Islands os Southeast Asia, the mountain areas of Ecuador and Colombia and the Atlantic Jungle along Brazilian coastal mountains, where there are more than fifteen hundred species.[4] Other important diversity areas are the mountains of Mesoamerica and the ones south of Himalaya, in India and China, besides the southeast of Africa, particularly Madagascar. Ecuador is the country where the largest number of orchid species is reported, up to 3,549,[5] imediately followed by Colombia, with 2,723,[5] New Guinea, 2,717,[5] and Brazil, with a total of 2,590.[5] Among others, Borneo, Sumatra, Madagascar, Venezuela and Costa Rica, are countries with high number of species.[6]

Habit

Orchids adapted to the most different environments. They may be terrestrial, growing on grassfields and savannahs among the grass, or on the soil of shady forests, epiphytic over trees or bushes, close to the soil sheltered from bright sunlight, or clore to the top of the trees and cacti, exposed to strong sunlight; they may be lithophyte growing over rocky soil or directly on the stones, they may be psamophytics oalong the sand of the beaches,saprophytic on decaying material over the soil or rarely acquatical, or paludicolous, in marshes and swamp areas. There is also an extreem case of a subterraneous species from Australia whose only the flowers occasionally emerge straight from the soil.[7]

The most common kinds of orchids in each of these areas are highly variable. On tropical regions, where the light and humidity are high, yet the competition for light with tree species is strong, the orchids tent to be predominat epiphytical, however, many species of terrestrial species, able to thrive without high amounts of light do exist too.[8] Looking for light, under the shadow of trees up to forty meters tall, this herbs grow over their branches and stems, at diverse heights, according to the necessities of each species. Their roots, exposed to the air, obtain most ot the nutrients from decaying material that acumulates around them, from the rains that washes the tree leaves from above, or from the air dust. Orchid roots are recovered by a spongy tissue called velamen. Associated with the velamen, most of orchids host a fungus known as Mycorrhyza that helps on decomposing of organic material breaking them into mineral salts, making easier their absortion by orchids. In extreem conditions, orchids may to some extent, absorve water and nutrients thorough the pores on their leaves, leaving to the roots only the function of sustaining the plant attached to the substract. No orchid is a parasite, what means their presence never damages their hosts, despite, in exceptional cases, some tree branches may not be strong enough to sustain the weight of a large colony and may end broken. There are many terrestrial orchids on tropical areas too, although, differently form the ones from temperate regions, many may keep growing almost constantly during most of the year.[8] The great amount of organic material available on forests soil favors the occurence of few saprophytic species of orchids without chlorophyll, which obtain all their nutrients from substances rejected by the processing of decomposing material by fungi associated to them.

In regions where the climate is colder, where the grassfilds are most common, or in dryer and rockier areas with small bushes, orchids are basicly terrestrial plants with buried roots, sometimes developes into tubercules which eneble them to resist winter and snow, ot to long droughs and occasional fires.[9] The snow might frost epiphytic species withouth sheltered roots to store the nutrients needed to shot a new grouth in springtime. Also the fires would enterely burn epiphyitic species. In this areas subject to most defined seasonal climatel, the plants normally hace a distinct period of dormancy while often their aerial segments die to avoid damages to their physiology due to extreem droughs or cold.

Some especies are considered endangered of extinction in the wild, both because of extensive collection, as due to the cut of forests for agriculture and even by the utilization of defoliating substances during wars from the past.[10] Surpringly enough, the majority of the endangered species are included among the most common under cultivation and the more frequently commercially grown.[11] Most of really rare species are not found on the lists of endangered species because they have no comercial value and low interest because of their tiny flowers or difficulty of culture. Ordinarily, for the same reasons, governments do not sponsor any surveys about the existing population of these in the wild and the few ones that exist are just occasional or made by private or academic researchers.[12]

Other important fact to consider against extinction is that each orchid fruit can contain hundreds of thousands seeds, and that the existence of two or three individuals unter culture may produce, in a few years, a fantastic number of plants, making the extinction threat of an orchid much different from the same threat to an animal, that just have one or few cubs each pregnancy.

Taxonomy

Orchidaceae is considered one of the largest, if not the largest, family among all plant families.[3] The number of species is close to 25 thousand, corresponding to about eight percent of all seed plants.[6] The exact number of accepted species is four times bigger than the mammal species and two times the birds.[13] These impressive numbers do not take into account the huge amount of new hybrids and varieties produced by orchid growers every year. Moroever, even today, hundreds of new species are described yearly, both because of revisions of long established genera but whose species were not well determinated, as due to new species discovered in nature. Only in 2008 the International Plant Names Index registrered more than four hundred new descriptions.

The orchid family was established when Antoine Laurent de Jussieu published his Genera Plantarum, in 1789.[14] However, before Jussieu's classification, Linnaeus already had described eight orchid genera which, nevertheless, did not form a family. At the time all epiphytic species belonged to the genus Epidendrum.[15] Other genus described by Linnaeus was Orchis, a greek word refering to the shape of two small tubercules that the species of this genus show, which resemble testicles.[16] As this was the first orchid genus to be formally described, from it derived the name of the whole family.[14]

Since Orchidaceae was proposed, the research on its species has not been interrupted. Their classification passed through numberless revisions and the amount of known genera they are divided has been increasing throughout the years, now reaching more than eight hundred.[17] Their exact number is not known because there is no consensus about the best way of splitting the genera. According to each reference, the list of accepted genera are diverse and the total number much different. A good example is a comparation between the number of genera published since 2002 to classify species before subordinated to genus Dendrobium, about thirty,[18] and the number of these which are actually accepted by the database of the Royal Botanic Garden, three or four.[6] The most recent trend is the classification based upon genetic, or molecular information called Phylogeny, which in theory reflects the evolutionary relations among each one of the species, groups of species, genera, and so forth. However, this system is comparatively new and not all researchers fully accept it, many still basing their conclusions mostly on morphologycal diagnosis. The debate is lively held on both fronts. One of the defensors of Phylogenetics is Mark Chase, who places morphology on a secondary level,[19] Among the morphologists one of the most noted is Carlyle August Luer, who since 1978 dedicated to study the species of subtribe Pleurothallidinae and thinks atha phylogenetic should be regarded only as an extra tool for now.[20] Luer has described about three thousand new species of orchids.

Orchidaceae is a family passing through an active cycle of evoluctionary development. Traditionaly, Biology considers the species concept as a group of beings that can breed producing fertile descendants. Orchid species are slightly different because they do not fit well in this concept. Not only most of the species can interbreed with several other producing fertile descendants, as most of the genera that belong to the same subtribe can do too.[21] It is not uncommon to encounter natural hybrids between diferent species and genera in the wild, and although almost all these plants are fertile, the are not more common just because as orchids are highly adaptated to their polinator, these hybrids may occur by chance and their particular resulting morphology are not really adaptated to the existing polinators. There are some rare exceptions, when these hybrids are result of breedings of two closely related species and still can be polinated by the same polinators of parent species. When this happens it is more likely that along the years a new species can appear. This may be the case of Cattleya × mesquitae. It is a natural hybrid discovered in 1996 in Goiás State in Brazil. We know know that this species is a result of a high degree of interbreeding of Cattleya walkeriana and Cattleya nobilior. As the result of this breeding is pollinated by the same agents of its parents, the crossing has been occuring again and again between the three species from the area along the ages, thus one of the original parents cannot be found there anymore. All original plants have crossed and faded. Today we know Cattleya × mesquitae is a hybrid because similar plants have been procuced by artificial breedings. Lou Menezes, its describer, claims that this species is so ancient that they have even evolved in nature, developing a fragrance that is not present on the hybrids artificially produced.[22] This is one of the ways a new species can appear in the wild. Cases like this are not uncommon among orchids, therefore many species are hard to circunscribe exactly because they result of different degrees of breedings between closely related species in a given area. Furthermore orchid hybrids produce variable descendents that may be closer to either one of the parents or an intermediate mixture of both.[23] It is also possible that one day many species described by Botanists may be proved to be in fact natural hybrids long stablished in nature.[8]

The circunscription of each species sometimes is complicated even further because many groups may be isolated and show subtle differences that some taxonomists may think are enough to establish independent species while other may think these are just natural variations of populations separated for long time but not yet important enough to justify the stablisment of another species.[12] Therefore the exact number of orchid species to be accepted by the scientific comunity is highly variable according to each reference. Today many taxonomists would rather classity these groups of species as superspecies or complexes of cryptic species. In these cases the differences between the extreem variations of a grrop con be clearly seen, but there are so many intermediate forms that placing exact limits between several species is almost impossible. There are many examples of these groups, as such the ones of Brasiliorchis picta, Anacheilium vespa, Heterotaxis crassifolia, and countless others.

The orchid family is formed by five subfamilies:

Plants with mealy or paste-like pollen, which ordinaily are not agregated into pellets, called pollinia, with two or three fertile long anthers, leaves with stealthing bases, elongated staminodium and labellum similar to the petals. It is the smallest subfamily, not split into tribes but only two genera and sixteen species from southeast Asia;
Plants with mealy or paste-like pollen, which ordinaily are not agregated into pollinia, with two oblong or oval anthers, leaves with stealthing bases, shelter-like staminodium and labellum generally saccate. This sbubfamily is split in five genera and 170 species spread though the world temperate areas, few encountered in tropical America;
Plants with mealy or paste-like pollen, which ordinaily are not agregated into pollinia, with one fertile incumbent anther only and leaves withouth stealthing bases. It is divided into two tribes, fifteen genera and 250 species spread throughout the humid tropical and subtropical areas of the world, and east of United States of America;
Plants with coherent pollen forming pollinia, with one fertile anther, erect or bent back, and convolute leaves but not very plicate, roots ordinarily fleshy or tuberouus. This subfamily is formed by six tribes and several subtribes, encompassing 208 genera and 3630 species distributed along almost all over the world, except the dryer deserts and polar areas;
Plants with coherent pollen forming pollinia and with one incumbent anther only, or with the anther bent back, but then with clearly plicate leaves and roots hardly ever fleshy. This is the largest subfamily, formed by several tribes and subtribes, more than five hundred genera and about twinty thousand species, distributed along the same areas of Orchidoideae, despite there are also subterrain species living at the deserts of Australia.

The division of the orchid species by genera is highly irregular. There is a great number of genera with one species only and some huge genera bearing more than a thousand. Despite many or these large genera are going through revision and breaking into smaller and handier genera many are not. We mention some of there larger genera as they were classified at the end of 2007:[6] Bulbophyllum with alomost two thousand species; Lepanthes, Stelis, Epidendrum, Pleurothallis, and Dendrobium with more than a thousand; Oncidium, Habenaria and Maxillaria bearing circa seven hundred; and Masdevallia, with more than five hundred.

Morphology

Among all the characteristics that distinguish Orchidaceae, very few are shared by all its species. This happens because orchids are a recent family in active evolution. Some groups of orchids derived from the core group of original ancestors very early, possibly during their first evolutionary steps, and have reatained many of their qualities, while others remained constant and derived much later. As the orchids have shown an enormous capacity of adaptation, this has led to an equaly huge number of variations and species.[24]

The most important characteristics shered by orchids are:[2]

  • The presence of the column, a structure orginated from the fusion of the flowers male and female sexual organs;
  • Pollen frequently aggregated into cartilaginous structures called pollinia;
  • very small seeds, almost without nutrients, formed by few cells, whigh only germinate when certain fungi are present;
  • Flowers of lateral simetry, not radial, composed by six segments, three external ones called sepals, and tree internal, called petals. From de later, one is different, called labellum, which normally ir responsible for pollinators atraction to the column, and participates actively of pollination mechanism.
  • Orchid flowers usually are presented inverted from the natural position due to a proccess known as ressupination, when during the bud growth, the ovarium twists itself 180º;
  • Most of epiphytic species has their roots recovered by a spongy tissue called vellamen;
  • The life sapn of an orchid is undeterminated becaus the grow indefinitely, continuously or during short anual periods, in theory for unlimited time. Few is known about the age an orchid can reach but there are records of their longevity both from the oldest specimen under culture at the Royal Botanic Garden, which is orlder than two hundred years, as for a plant that belongs to the Círculo Americanense de Orquidófilos, already cultivated for more than one hundred years.

For all named characteristics there are abundant exceptions, however, all orchids share, at different degrees, several of them.[2]

Growth

Orchids growth occurs in several diverent patterns, it may be continuous or seazonal, sympodial or monopodial, grouped ou spaced, ascendent or pendent, aerial or buried.[25] Depending upon the environment condition, certain growth forms are predominant. On tropical areas cuntinuous growth is more common, despite there are also a high number of species of seazonal growth. In areas subjecto to droughs or intense cold, the seazonal growth is the rule. Monopodial orchids ususally grow continuously, sympodial, ordinarily show certain seazonality.[8]

Roots

Orchids have no primary roots, that are main central roots where secondary roots grow from, but only the secondary roots, which start directly from the stem and, ocasionally, from other secondary roots. Frequently the roots act as a storage of nutrients and water, helping the plant to retain and acumulate nutritional substances that deposit on their bases. In some cases the roots are chlorophyllated organs capable of carrying photosyntheses during the periods when the plants loose their leaves. Their roots show varied thicknesses, from highly thin to extremelly thick. Roots structure is highly variable among orchid genera, according to the way and the places they grow.[25]

The epiphytic species generally present robust roots, cylindrical when aerial, which become flatter after attached to the substract. They are frequently recovered by the vellamen, which is a thick spongy tissue that is very important to enable orchids to quickly absorb high quantities of water from the rains and even humidity from the air.[24]

The terrestrial species normaly bear some roots thickened into small or large strucures that resenble tubercules, which may be spherical to elongated cylinders which act as storage of water and nutrients, replacing the role carried by the pseudobulbs usually present on epiphytic species. Occasionally these tubercules split from the mother plant originating new plants.[24]

The roots life time varies according to environmental conditions and generally is inferior to the stem life time. New roots usually shot during or at the end of each plant vegetative growth period. Despite this is not the primary nutritional source of orchids, they usually benefit from a kind of symbiosis or association with a fungus called Micorrhyza lodged on the vellamen exterior cells of their roots and excretes several nitrients directly absorbed their roots.[24]

Stems

On epiphytic species of sympodial growth the stem usually is formed by two segments, one of them, called rhyzome, shows reptant growth, which means it grows along the substract, and can be short or elongated, thin or thick; the other segment is aerial and may or may not be thickened into a structure called pseudobulb, which acts as water and nutrients storage. In some epiphytic genera, particularly the ones related to genus Huntleya, the secondary, or aerial stem, is reduced to an inconspicuous node which originates the leaves. Sympodial orchids usually show seazonal growth and new secondary stems are added each period.[26]

On epiphytic species of monopodial growth the stem is formed by the aerial segment only. It may be erect or pendent and its extremity growns continuously forming new leaves and ocasional lateral roots or new growths along the stem. The stem of this kind of orchids is never thickened into pseudobulbs, however their leaves and roots ordinarily are comparatively thicker than the epiphitical ones, as thet frequently help retaining water and nutrients.[25]

Terrestrial species may or may not have developed stems and these, different from epiphytical orchids which always show perenial stems, may be partialy or enterely deciduous. Some terrestrial orchids present very long stems, which sometimes reach more than six meters of length.[25]


Hybrids

Fertile orchid hybrids can be artificialy crossed with other species of the same or of other genera and produce new generations of fertile hybrids. today there are hybrids involving up to eight genera and as time passes it is likely even more genera will be crossed. The Royal Horticultural Society is responsible for keeping the records of these hybrids up to date. The capacity orchids have to interbreed is one of their carachtheristics more valuated by growers because it enables them to mix the species obtaining endless combinations of new colors and patterns.

References

  1. ↑ Ernst Mayr Biography: The Darwin of the 20th Century. Sourced on 22nd November 2007.
  2. ↑ 2.0 2.1 2.2 Dressler, Robert L. (1981). The Orchids: Natural History and Classification. Harvard University Press. ISBN 0674875257.
  3. ↑ 3.0 3.1 J.T. Atwood (1986). The size of the Orchidaceae and the systematic ditribution of epiphytic orchids. Selbyana 9, 171-86.
  4. ↑ Guido Pabst & Fritz Dungs (1975) Orchidaceae Brasilienses vol. 1, Brucke-Verlag Kurt Schmersow, Hildesheim. ISBN 3871050106
  5. ↑ 5.0 5.1 5.2 5.3 R. Govaerts, M.A. Campacci (Brazil, 2005), D. Holland Baptista (Brazil, 2005), P.Cribb (K, 2003), Alex George (K, 2003), K.Kreuz (2004, Europe), J.Wood (K, 2003, Europe) World Checklist of Orchidaceae. The Board of Trustees of the Royal Botanic Gardens, Kew. Checklists by region and Botanical countries.Published on Internet access 1st March 2009.
  6. ↑ 6.0 6.1 6.2 6.3 R. Govaerts, et al. World Checklist of Orchidaceae. The Board of Trustees of the Royal Botanic Gardens, Kew. Published on Internet access 1st March 2009.
  7. ↑ N. Hoffman e A. Brown (1998). Orchids of South-west Australia. University of Western Australia Press, Nedlands.Rev. 2nd ed. with suppl. ISBN 1876268182
  8. ↑ 8.0 8.1 8.2 8.3 Hoehne, Frederico Carlos (1940) Flora Brasílica, Part.1, Volume 12.1; 1 - 12 - Orchidaceae, introdução. Secretaria da Agricultura, Indústria e Comércio de São Paulo - Brasil, 1940.
  9. ↑ Karsten H. K. Wodrich e A. A. Balkema. (1997). Growing South African Indigenous Orchids. ISBN 978-9054106500.
  10. ↑ Leonid Averyanov, Phillip Cribb, Phan Le Loc, and Nguyen Tien Hiep. (2003). Slipper Orchids of Vietnam. Timber Press, Portland, Oregon. ISBN 0881925926
  11. ↑ Eric Hansen (2000). Orchid Fever. Methuen. ISBN 0413747506.
  12. ↑ 12.0 12.1 Chan, C.L. (1994). The species concept, pp. 27 in Orchids Of Borneo. The Sabah Society and Kew: Bentham-Moxon Trust, Volume 1. ISBN 967 9994732
  13. ↑ Yohan Pillon e Mark W.Chase. (2006). Taxonomic Exaggeration and its Effects on Orchid Conservation. Conservation Biology vol. 21 Issue 1, Pages 263 - 265.
  14. ↑ 14.0 14.1 Antonii Laurentii de Jussieu (1789). Genera plantarum: secundum ordines naturales disposita, juxta methodum in Horto regio parisiensi exaratam, anno M.DCC.LXXIV. Parisiis: apud viduam Herissant et Theophilum Barrois.
  15. ↑ Caroli Linnaei (1753). Species plantarum: exhibentes plantas rite cognitas, ad genera relatas, cum differentiis specificis, nominibus trivialibus, synonymis selectis, locis natalibus, secundum systema sexuale digestas... Holmiae: Impensis Laurentii Salvii.
  16. ↑ Pedáneo Dioscórides (50-70 AD). De materia medica.
  17. ↑ Phillip Cribb (2001) Orchidaceae. Em A. M. Pridgeon, P. J. Cribb, M. W. Chase, and F. N. Rasmussen eds., Genera Orchidacearum, vol. 1. Oxford University Press, Oxford, UK ISBN 0198505132.
  18. ↑ Clements, M.A. and D.L. Jones (2002). Nomenclatural changes in the Dendrobieae (Orchidaceae) 1: The Australasian region. Orchadian 13(11): 485-497.
  19. ↑ Mark W. Chase (2001) Molecular Systematics, Parcimony and Orchid Classification. Em A. M. Pridgeon, P. J. Cribb, M. W. Chase, and F. N. Rasmussen eds., Genera Orchidacearum, vol. 1: pp.83. Oxford University Press, Oxford, UK ISBN 0198505132.
  20. ↑ Carlyle August Luer (2004). Icones Pleurothallidinarum, Volume XXVI, A Second Century of New Species of Stelis of Ecuador. pp.253. Missouri Botanical Garden. ISBN 1930723292
  21. ↑ de Queiroz, K. (2005). Ernst Mayr and the modern concept of species in Proc. Natl. Acad. Sci. U.S.A. volume 102 Suppl.1 pp. 6600–7 pmid=15851674
  22. ↑ Menezes, Lou. C. Cattleya × mesquitae in Boletim CAOB vol.26 p.24. São Paulo, 1996.
  23. ↑ Hoehne, Frederico Carlos (1953) Flora Brasílica, Fascículo 10, Volume 12.7; 140 - Maxillaria heterophyla pp. 313.
  24. ↑ 24.0 24.1 24.2 24.3 Joseph Arditti (1992) Fundamentals of Orchid Biology. Wiley & Sons. ISBN 9780471549062.
  25. ↑ 25.0 25.1 25.2 25.3 Phillip Cribb (2001) Morphology of Orchidaceae. Em A. M. Pridgeon, P. J. Cribb, M. W. Chase, and F. N. Rasmussen eds., Genera Orchidacearum, vol. 1. Oxford University Press, Oxford, UK ISBN 0198505132.
  26. ↑ Patricia A. Harding (2008). Huntleyas and Related Orchids. Timber Press. ISBN 9780881928846.
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