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The family Orchidaceae, consisting of approximately 450 genera and over 17000 species, has a worldwide distribution, but with the largest number of species in the tropics. Various life forms occur: terrestrial, epiphytic, lithophytic (plants growing on cliffs or rock faces), as well as a few species living entirely below ground until flowering. Several orchid species remain achlorophyllous during their entire life cycle and are, therefore, myco-heterotrophic, depending on fungi for carbon compounds derived either from the breakdown of organic matter in the soil or from mycorrhizal linkages with autotrophic plants.
Using tissue culture methods, many orchid species are grown commercially for the floriculture industry. The genus Vanilla is grown for its seed pod extract, which is used as a flavouring in the food industry. Many orchid species can now be propagated from seeds in vitro by supplying the germinating seeds with a source of simple sugars, or with the appropriate fungus including media containing a complex organic source. As a result, species or hybrids with showy and unusual flowers can be produced in large numbers for the flower market.
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