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).
- American Orchid Society 2013. Retrieved October 27, 2013 from http://www.aos.org/default.aspx?id=1
- Bulpitt, C.J.; Y. Li, G.F. Bulpitt; J. Wang 2007. The use of orchids in Chinese medicine. J R Soc Med. 100(12): 558–563. PMCID: PMC2121637. Available online at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2121637/#__ffn_sectitle
- Cameron, K.M.; M.W. Chase; W.M. Whitten; P.J. Kores; D.C. Jarrell; V.A. Albert; T. Yukawa; H.G. Hills and D.H. Goldman, 1999. A phylogenetic analysis of the Orchidaceae: evidence from rbcL nucleotide sequences. Am. J. Bot. February 1999 vol. 86 no. 2 208-224. Available online at http://www.amjbot.org/content/86/2/208.full
- Gott, B. 2008. Indigenous use of plants in south-eastern Australia. Telopea 12(2):215-226. Retrieved November 7, 2013 from http://www.rbgsyd.nsw.gov.au/__data/assets/pdf_file/0004/95395/Tel122215Got.pdf
- Gustafsson, A.L.S. Verola, C.F., and Antonelli, A. 2010. Reassessing the temporal evolution of orchids with new fossils and a Bayesian relaxed clock, with implications for the diversification of the rare South American genus Hoffmannseggella (Orchidaceae: Epidendroideae). BMC Evol. Biol. 10: 177. doi:10.1185/1471-2148-10-177. Available online at http://www.biomedcentral.com/1471-2148/10/177
- Kew Royal Botanic Gardens. The orchid family (Orchidaceae). Retrieved November 7, 2013 from http://www.kew.org/plants-fungi/for-gardeners/orchids/ and http://www.kew.org/science/orchids/whystudy.html
- Ramírez, S.R.; B. Gravendeel, R.B. Singer, C.R. Marshall and N.E. Pierce, 2007. "Dating the origin of the Orchidaceae from a fossil orchid with its pollinator". Nature 448 (7157): 1042–1042. doi:10.1038/nature06039. PMID 17728756.
- Romero-González, G.A.; G.C. Fernández-Concha; R.L. Dressler; L.K. Magrath and G.W. Argus, 2003. Orchidaceae Jussieu. FNA Vol. 26 Page 15, 16, 17, 26, 27, 490, 491, 617. Retrieved November 7, 2013 from http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=10638.
- Stevens, P. F. (2001 onwards). Angiosperm Phylogeny Website. Version 12, July 2012 [and more or less continuously updated since]." http://www.mobot.org/mobot/research/apweb/welcome.html
- Stewart, K. and Percival B. 1997. Bush foods of New South Wales. Royal Botanic Gardens, Sydney 1997. Available online at http://www.rbgsyd.nsw.gov.au/__data/assets/pdf_file/0006/85542/Bushfoodsbook.pdf
- The Plant List, 2010. Version 1. Published on the Internet; http://www.theplantlist.org/browse/A/Orchidaceae/ (accessed 6 November 6, 2013).
- The Royal Botanic Gardens and Domain Trust, 2013. Aboriginal Bush Foods. Retrieved November 7, 2013 from http://www.rbgsyd.nsw.gov.au/plant_info/aboriginal_bush_foods.
- Williams, N.H. 2013. The Orchid Tree: a phylogeny of epiphytes (mostly) on the tree of life. Florida Museum of Natural History. Retrieved November 7, 2013 from http://www.flmnh.ufl.edu/herbarium/orchidatol/
- eResources Unit, 2004. Function of orchid mychorrizas. In Fungal Biology, website. Online learning resources, School of Biological Sciences, University of Sydney. Retrieved November 6, 2013 from http://bugs.bio.usyd.edu.au/learning/resources/Mycology/Plant_Interactions/Mycorrhizas/Orchid/orchidFunction.shtml#nutrientExchange
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