Temporal range: 70.0–0Ma Late Cretaceous to Recent
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 the Sichuan–Hubei region 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. The other Sequoioideae and several other genera have been transferred from the former Taxodiaceae family to Cupressaceae based on DNA analysis.
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.
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 in the United States.
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".
While the bark and foliage are similar to another closely related redwood genus Sequoia, Metasequoia differs from the California redwood in that it is deciduous like Taxodium distichum (bald cypress), and like that species, older specimens form wide buttresses on the lower trunk. It is a fast-growing tree to 130–150 feet (40–45 m) tall and 6 feet (2 m) in trunk diameter in cultivation so far (with the potential to grow to even greater heights).
The leaves are opposite, 0.4-1.25 inches (1–3 cm) long, and bright fresh green, turning a foxy red-brown in fall. The pollen cones are 0.25 inch (6 mm) long, produced on long spikes in early spring; they are only produced on trees growing in regions with hot summers. The cones are globose to ovoid, 0.6-1.0 inches (1.5-2.5 cm) in diameter with 16–28 scales, arranged in opposite pairs in four rows, each pair at right angles to the adjacent pair; they mature in about 8–9 months after pollination.
Metasequoia was first described as a fossil from the Mesozoic Era by Shigeru Miki in 1941, but in 1944, a small stand of an unidentified tree species was discovered in China in Modaoxi (磨刀溪; presently, Moudao (谋道), in Lichuan County, Hubei) by Zhan Wang. Due to World War II, these were not studied further until 1946, and only finally described as a new living species of Metasequoia in 1948 by Wan Chun Cheng and Hu Hsen Hsu. In 1948, the Arnold Arboretum of Harvard University sent an expedition to collect seeds and, soon after, seedling trees were distributed to various universities and arboreta worldwide for growth trials.
Presently, a number of natural Metasequoia populations exist in the hills and wetlands of Hubei's Lichuan County. Most of them are small, with fewer than 30 trees each; however, the largest of them, in Xiaohe Valley, is estimated to consist of around 5,400 trees. A few trees are also said to exist in the neighboring Hunan Province.
Metasequoia in gardens, parks and streets
Dawn redwoods are fast-growing trees. They will grow too large for small gardens, but can be good in a wide range of larger gardens and parks. Although they live in wet sites in their native habitat they will also tolerate dry soils. Unlike most conifers, their deciduous habit means they do not cast too much shade in winter, and they can even be seen growing as street trees in London.
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