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''Metasequoia'' (dawn redwood) is a fast-growing, deciduous tree, and the sole living species, ''Metasequoia glyptostroboides'', is one of three species of conifers known as redwoods. It is native to Lichuan county in the Hubei province of China. Although the least tall of the redwoods, it grows to at least 200 feet (60 meters) in height. Local villagers refer to the original tree from which most others derive as ''Shui-sa'', or "water fir", which is part of a local shrine. Since that tree's rediscovery in 1944, the dawn redwood has become a popular ornamental. Together with ''Sequoia sempervirens'' (coast redwood) and ''Sequoiadendron giganteum'' (giant sequoia) of California, ''Metasequoia'' is classified in the Cupressaceae subfamily Sequoioideae. Although ''M. glyptostroboides'' is the only living species in its genus, three fossil species are known, as well. Sequoioideae and several other genera have been transferred from the former Taxodiaceae family to Cupressaceae based on DNA analysis. ==Paleontology== ''Metasequoia'' redwood fossils are known from many areas in the Northern Hemisphere; more than 20 fossil species have been named (some were even identified as the genus ''Sequoia''), but are considered as just three species, ''M. foxii'', ''M. milleri'', and ''M. occidentalis''. During the Paleocene and Eocene, extensive forests of ''Metasequoia'' occurred as far north as Strathcona Fiord on Ellesmere Island and sites on Axel Heiberg Island (northern Canada) at around 80° N latitude. ''Metasequoia'' was likely deciduous by this time. Given that the high latitudes in this period were warm and tropical, it is hypothesized that the deciduous habit evolved in response to the unusual light availability patterns, not to major seasonal variations in temperature. During three months in the summer, the sun would shine continuously, while three months of the winter would be complete darkness. It is also hypothesized that the change from evergreen to deciduous habit occurred before colonizing the high latitudes and was the reason ''Metasequoia'' was dominant in the north.〔 In LePage ''et al'' (2005).〕 Large petrified trunks and stumps of the extinct ''Metasequoia occidentalis'' (sometimes identified as ''Sequoia occidentalis'') also make up the major portion of Tertiary fossil plant material in the badlands of western North Dakota. The trees are well known from late Cretaceous to Miocene strata, but no fossils are known after that. Before its discovery, the taxon was believed to have become extinct during the Miocene; when it was discovered extant, it was heralded as a "living fossil". 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Metasequoia」の詳細全文を読む スポンサード リンク
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