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Sequoia sempervirens
''Sequoia sempervirens'' 〔''Sunset Western Garden Book,'' 1995:606–607
〕 is the sole living species of the genus ''Sequoia'' in the cypress family Cupressaceae (formerly treated in Taxodiaceae). Common names include coast redwood, coastal redwood and California redwood.〔The related ''Sequoiadendron giganteum'' is commonly referred to as "giant redwood".〕 It is an evergreen, long-lived, monoecious tree living 1,200–1,800 years or more. This species includes the tallest living trees on Earth, reaching up to in height (without the roots) and up to in diameter at breast height / dbh.〔 These trees are also among the oldest living things on Earth. Before commercial logging and clearing began by the 1850s, this massive tree occurred naturally in an estimated along much of coastal California (excluding southern California where rainfall is not sufficient) and the southwestern corner of coastal Oregon within the United States. An estimated 70% or more of ancient old-growth redwood trees have been displaced by environmental changes or cut down.〔Kelly, D. and G. Braasch. 1988. Secrets of the old growth forest. Gibbs Smith, Layton, Utah: 1–99.〕
The name sequoia sometimes refers to the subfamily Sequoioideae, which includes ''S. sempervirens'' along with ''Sequoiadendron'' (giant sequoia) and ''Metasequoia'' (dawn redwood). On its own, the term redwood usually refers to the coast redwood, which is covered in this article, and not to the other two species.
==Taxonomy==
Scottish botanist David Don described the redwood as the evergreen taxodium (''Taxodium sempervirens'') in his colleague Aylmer Bourke Lambert's 1824 work ''A description of the genus Pinus''. Austrian botanist Stephan Endlicher erected the genus ''Sequoia'' in his 1847 work ''Synopsis coniferarum'', giving the redwood its current binomial name of ''Sequoia sempervirens''. The redwood is one of three living species, each in its own genus, in the subfamily Sequoioideae. Molecular studies have shown the three to be each other's closest relatives, generally with the redwood and giant sequoia (''Sequoiadendron giganteum'') as each other's closest relatives. However, Yang and colleagues in 2010 queried the polyploid state of the redwood and speculate that it may have arisen as an ancient hybrid between ancestors of the giant sequoia and dawn redwood (''Metasequoia''). Using two different single copy nuclear genes, LFY and NLY, to generate phylogenetic trees, they found that ''Sequoia'' was clustered with ''Metasequoia'' in the tree generated using the LFY gene, but with ''Sequoiadendron ''in the tree generated with the NLY gene. Further analysis strongly supported the hypothesis that ''Sequoia'' was the result of a hybridization event involving ''Metasequoia'' and ''Sequoiadendron''. Thus, Yang and colleagues hypothesize that the inconsistent relationships among ''Metasequoia'', ''Sequoia,'' and ''Sequoiadendron'' could be a sign of reticulate evolution (in which two species hybridize and give rise to a third) among the three genera. However, the long evolutionary history of the three genera (the earliest fossil remains being from the Jurassic) make resolving the specifics of when and how ''Sequoia'' originated once and for all a difficult matter—especially since it in part depends on an incomplete fossil record.
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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