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Pilosocereus robinii
''Pilosocereus robinii'' is a species of cactus known by the common name Key tree-cactus. It is native to the Florida Keys in the United States.〔USFWS. (''Pilosocereus robinii'' Five-year Review. ) August 2010.〕 It may occur in Cuba, but any populations there are unconfirmed.〔〔(''Pilosocereus robinii''. ) Center for Plant Conservation.〕 It has been reported from Puerto Rico,〔(''Pilosocereus robinii''. ) The Nature Conservancy.〕 the Virgin Islands,〔 and Mexico.〔 It is a rare species which is threatened by the loss of its habitat.〔 It is a federally listed endangered species of the United States.
This is a large cactus growing erect, often with many parallel or spreading branches. It may become a tree up to tall. The stem is green in color with a blue tinge when young and has 9 to 13 ribs. The areoles are covered in long or short hairs and have up to 31 spines each. The spines are no more than a centimeter long. The bell-shaped flower is long. The outer tepals are greenish with brownish midstripes and the inner tepals are white.〔 The flower has a scent similar to garlic.〔〔 It opens at night and contains a sweet nectar.〔 The taxonomy of the species and other ''Pilosocereus'' is not certain. This species is often included in the description of ''Pilosocereus polygonus''.〔〔
This cactus grows in upland tropical hardwood hammocks on limestone or coral substrates. It sometimes grows on sparsely vegetated coral rock〔 and just above the high tide mark.〔 Storm surges and sea level rise may inundate its shoreline habitat and increase the salinity beyond the tolerable range for the cactus.〔〔
Other threats to the species include the destruction of its habitat during development. Populations on the Upper and Lower Matecumbe Keys have been mostly eliminated due to residential development.〔 Development also leads to habitat fragmentation. Hurricanes are a threat to the cactus because the winds can break cactus branches or bring down taller vegetation, causing injury; however, hurricane action may open the canopy, providing sunlight to the cactus, which may be beneficial. As of 2009 there are seven known populations of this plant in Florida, located on four of the Florida Keys.〔
==References==
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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