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Orchidaceae, commonly referred to as the Orchid
family, is a morphologically diverse and widespread family of monocots. It
is currently believed to be the second largest family of flowering plants
(only the Asteraceae is larger), with between 21,950 and 26,049 currently
accepted species, found in 880 genera.[1][2] The number of orchid species
equals more than twice the number of bird species, and about four times the
number of mammal species. It also encompasses about 6–11% of all seed
plants.[3] The largest genera are Bulbophyllum (2,000 species), Epidendrum
(1,500 species), Dendrobium (1,400 species) and Pleurothallis (1,000
species).
The family also includes Vanilla (the genus of the vanilla plant), Orchis
(type genus) and many commonly cultivated plants like some Phalaenopsis or
Cattleya. Moreover, since the introduction of tropical species in the 19th
century, horticulturists have produced more than 100,000 hybrids and
cultivars.
Distribution
Orchidaceae are cosmopolitan, occurring in almost every habitat apart from
deserts and glaciers. The great majority are to be found in the tropics,
mostly Asia, South America and Central America, but they are also found
above the Arctic Circle, in southern Patagonia, and even two species of
Nematoceras on Macquarie Island, close to Antarctica.
The following list gives a rough overview of their distribution:
* tropical America: 250 to 270 genera
* tropical Asia: 260 to 300 genera
* tropical Africa: 230 to 270 genera
* Oceania: 50 to 70 genera
* Europe and temperate Asia: 40 to 60 genera
* North America: 20 to 26 genera
Stem and roots
All orchids are perennial herbs and lack any permanent woody structure.
Orchids can grow according to two patterns:
* Monopodial: The stem grows from a single bud, leaves are added from the
apex each year and the stem grows longer
accordingly. The stem of orchids with a monopodial growth can reach several
metres in length, as in Vanda and Vanilla.
* Sympodial: The plant produces a series of adjacent shoots which grow to a
certain size, bloom and then stop growing, to be then replaced. Sympodial
orchids grow laterally rather than vertically, following the surface of
their support. The growth continues by development of new leads, with their
own leaves and roots, sprouting from or next to those of the previous year,
as in Cattleya. While a new lead is developing, the rhizome may start its
growth again from a so-called 'eye', an undeveloped bud, thereby branching.
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