orchids
Orchidaceae
EOL Text
The Orchidaceae, known as the orchid family, underwent a spectacularly diverse radiation since its late Cretaceous origin 83-75 million years ago to become one of the two most speciose plant families around today (the other being the Asteraceae), and make up more than one third of monocot species (Ramírez et al. 2007; Gustafsson et al. 2010). Taxonomy of the orchid family is difficult and dynamic, because it is so large (now approximately 27,000+ accepted species) and many new species are described annually (see references listed at the Orchid Tree, Florida Museum of Natural History: http://www.flmnh.ufl.edu/orchidatol/references/orchidATOLrefs.htm; Cameron 1999 and references therein; Williams 2013). Many morphological and molecular studies break down the family into five monophyletic subfamilies: Apostasioideae, Cypripedioideae, Epidendroideae, Orchidoideae, and Vanilloideae, of which Epidendroideae is by far the largest, containing about 3/5 of orchid species (see references listed at the Orchid Tree, Florida Museum of Natural History: http://www.flmnh.ufl.edu/orchidatol/references/orchidATOLrefs.htm; Cameron 1999 and references therein; Williams 2013; The Plant List 2010).
Orchids live in nearly all ecosystems around the world except glaciers, true desert and open water, although tropical areas especially in Asia, Africa and the Americas are the hot spots of diversity. Most grow as epiphytes on other plants, rocks or static objects for support and derive their nutrients and water from the atmosphere and debris, however many species grow in the ground in forest or grassland areas. Some are parasites of fungi. Some, such as species in the subfamily Vanilloideae grow as lianas (a woody vine) that can reach sizes up to 20 m. (60 feet) or more in length; the tiny Bulbophyllum minutissimum is only 3-4 mm (0.16-0.2 inches) tall. (Kew RBG 2013; Williams 2013; Stephens 2013).
Orchids are monocots, perennial herbs with simple leaves and parallel veins, and are well known for the rich diversity of their flower structures. While some have single flowers, most have inflorescences with multiple flowers arranged around a stalk. The flowers are pollinated by insects, in some cases by birds, and it is common for flowers to have petals modified into perches or guides for their pollinators. Orchids have a dizzying array of pollination syndromes, some fantastically complex. About a third of orchid species mimic an aspect of their pollinator’s biology in order to trick the pollinator into visiting the flower without providing nectar or other reward. For example, the bee orchids (genus Ophrys) accurately mimic a female bee, right down to the smell, to entice male visitation. The flower of Darwin’s orchid, Angraecum sesquipedale, has an extremely long spur with nectar at the end, which led Charles Darwin to posit that this species was pollinated by a moth with a proboscis of unprecedented length. His theory was validated when the pollinator was discovered, years after Darwin’s death. In reference to the amazing pollination biology of genus Catasetum, which propel large, sticky pollen capsules at their pollinators, Darwin wrote in a 1861 letter to then director of Kew Gardens, Joseph Hooker: “I was never more interested in any subject in all my life, than in this of orchids” (Williams 2013; Kew RBG 2013; Stevens 2013).
All orchids have inferior ovaries which develop into a capsule with (usually six) compartments containing up to millions of minute seeds (as small as 150 µm), excellent wind dispersers. One plant typically produces 74 million seeds. In order to germinate, orchid seeds require a symbiotic interaction with species-specific bascidiomycete fungus, which enters the seed. This allows the orchid seed, which has no nutrient reserves, to gain necessary nutrients directly from the fungi and form a protocorm, a unique embryonic structure made up of a mass of cells found in no other flowering plants. After facilitating germination, the colonizing fungal symbiont subsequently nourishes the seedling and especially in the case of epiphytic and parasitic (non-photosynthetic) orchids, the fungal interaction often persists to transfer nutrients and minerals to the fully developed orchid. It is not clear how the fungi benefit from this interaction. The orchid apparently controls and regulates the timing and degree of fungal association, presumably providing sufficient reason for the fungi to colonize and re-associate with the plant, often on a seasonal cycle (eResources Unit, 2004; Kew RBG; Stevens 2013; Williams 2013).
The charisma of orchids and their biology have long excited (obsessed!) botanists and the general public alike, and many varieties and hybrids are widely cultivated; this passion has inspired intrepid collecting expeditions and spawned hundreds of orchid societies and clubs around the world, spawning a global cultivation industry worth nine-billion dollars annually. Each year 3000-4000 new hybrid names enter the International Orchid Register (American Orchid Society 2013). Most cultivars are tropical or sub-tropical. Many orchid species are threatened in the wild, due to over collection and habitat degradation. Cites highly restricts international import/export of orchids; all orchids are on the Appendix II list or higher (Kew RBG 2013; Williams 2013).
As well as providing significant botanical interest, some orchids have food uses. Vanilla, for example, is a commercially important and widely used flavoring extracted from the dried pods of several species of genus Vanilla; commercially grown vanilla requires hand pollination of the flower making this is one of the world’s most expensive spices. Some orchids produce edible tubers; Australian desert and forest orchids, for example, are historically eaten by Aboriginals (Stewart and Percival 1997; The Royal Botanic Gardens and Domain Trust, 2013; Gott 2008). Orchids also have ancient origins in traditional medicine in many cultures, including Chinese medicine (Bulpitt et al. 2007).
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Rights holder/Author | Dana Campbell, Dana Campbell |
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There are over 21,000 species of orchid. They are likely the largest family of flowering plants. Orchid flowers are special because they grow upside down. A long upper petal grows on the bottom of the flower. This makes a good landing spot for pollinators.
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Perennial, terrestrial or epiphytic herbs with rhizomes, tubers or corms. Stems sometimes swollen at the base (pseudobulbs). Leaves alternate or rarely opposite (e.g. some spp. of Disperis), entire. Inflorescence a spike, raceme or panicle. Flowers bracteate, bisexual, zygomorphic, usually twisted through 180° (resupinate), occasionally not twisted or twisted through 360°. Perianth epigynous; perianth segments 6, usually free, arranged in 2 whorls; both whorls similar or outer whorl (sepals) calyx-like and inner whorl (petals) corolla-like or very reduced. Central segment of outer whorl (dorsal sepal) often different in shape and size to the lateral; central segment of inner whorl (lip or labellum) often lobed or spurred. Stamen 1, united with the style to form the column. Pollen aggregated into masses (pollinia). Ovary inferior, 1-locular. Stigmas 3, fertile or more usually 2 lateral fertile, the other an outgrowth (rostellum), lying between the anthers and the lateral stigmas. Part of the rostellum is often modified into sticky discs (viscidia) to which the pollinia are attached by 1-2 stalks (stipes). Whole structure of pollinia, stipes and viscidia form the pollinarium. Fruit a capsule, often longitudinally ribbed. Seeds minute, very numerous, without endosperm.
In Great Britain and/or Ireland:
Plant / resting place / on
Anaphothrips orchidaceus may be found on live Orchidaceae
Plant / associate
basidiome of Ceratobasidium cornigerum is associated with mycorrhiza of Orchidaceae
Foodplant / spot causer
Cladosporium dematiaceous anamorph of Cladosporium orchidearum causes spots on live Orchidaceae
Plant / resting place / within
puparium of Delina nigrita may be found in rootstock of Orchidaceae
Foodplant / feeds on
Heliothrips haemorrhoidalis feeds on Orchidaceae
Foodplant / sap sucker
Myzus persicae sucks sap of Orchidaceae
Foodplant / pathogen
Odontoglossum Ringspot virus infects and damages yellowish spotted leaf (young) of Orchidaceae
Foodplant / open feeder
subterranean larva of Otiorhynchus sulcatus grazes on root of Orchidaceae
Foodplant / miner
solitary, then gregarious larva of Parallelomma vittatum mines live leaf of Orchidaceae
Remarks: season: summer
Foodplant / sap sucker
Saissetia coffeae sucks sap of live leaf of Orchidaceae
Foodplant / mycorrhiza
Thanatephorus ochraceus is mycorrhizal with live root of Orchidaceae
Foodplant / feeds on
adult of Thrips tabaci feeds on live leaf of Orchidaceae
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Roots absorb moisture from humid air: orchids
Some orchids absorb moisture from humid air via aerial roots.
"Orchids of many kinds have also adopted this high life. They lack the ponds that sustain the bromeliads, so they must collect their nourishment in other ways. Some dangle their roots in the air, absorbing moisture from the humid atmosphere and rely on the tiny amount of nutriments it might have dissolved on its descent through the forest vegetation. Others spread their roots over the surface of the branches and collect the water that has trickled through the leaves and dripped from branch to branch, gathering a little nutriment on the way." (Attenborough 1995:166)
Learn more about this functional adaptation.
- Attenborough, D. 1995. The Private Life of Plants: A Natural History of Plant Behavior. London: BBC Books. 320 p.
License | http://creativecommons.org/licenses/by-nc/3.0/ |
Rights holder/Author | (c) 2008-2009 The Biomimicry Institute |
Source | http://www.asknature.org/strategy/e148032a7ba117a13ec5d22b7a7569ba |
More successful pollination: orchids
The flowers of individual plants of a given orchid species improve the odds for successful pollination by producing a scent unique to that plant.
"However, all individual plants of one species, while they produce a scent that mimics the female pheromone in its essentials, do not smell exactly the same. Each plant differs sufficiently from others to suggest to the bee that this next one, with a slightly different fragrance, will give him the satisfaction that has eluded him so far." (Attenborough 1995:129)
Learn more about this functional adaptation.
- Attenborough, D. 1995. The Private Life of Plants: A Natural History of Plant Behavior. London: BBC Books. 320 p.
License | http://creativecommons.org/licenses/by-nc/3.0/ |
Rights holder/Author | (c) 2008-2009 The Biomimicry Institute |
Source | http://www.asknature.org/strategy/d48ca4c563232dbecd73e2e05fed81d8 |
Pollen fastens to a bee's head: orchids
The column of some orchids descends from the top of the flower when a male bee lands and deposits pollinia on its head.
With European orchids, "If and when a male bee finds the flower, he settles upon the lip, grasping it in exactly the same way as he grasps a female bee, and tries to copulate, thrusting the tip of his abdomen into the fringe of long hairs at the end of the lip. He fails, of course, but in the process, a curved column that houses both male and female organs, descends from the top of the orchid and glues a pair of pollinia to his head. If the next orchid he visits has already despatched its pollinia, then the column will pick up the one he carries and the orchid is fertilised." (Attenborough 1995:126)
Learn more about this functional adaptation.
- Attenborough, D. 1995. The Private Life of Plants: A Natural History of Plant Behavior. London: BBC Books. 320 p.
License | http://creativecommons.org/licenses/by-nc/3.0/ |
Rights holder/Author | (c) 2008-2009 The Biomimicry Institute |
Source | http://www.asknature.org/strategy/f2a7b6dbf0593948d452e91128a98909 |
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