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Metasequoia
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Metasequoia (Dawn Redwood) is a fast growing tree genus in the conifer family Cupressaceae of which Metasequoia glyptostroboides, native to the Sichuan-Hubei region of China, is the only living species. Metasequoia, along with Sequoia, Sequoiadendron and several other genera, were transferred from the Taxodiaceae family to Cupressaceae using DNA analysis. M. glyptostroboides is the only extant species in its genus, but three fossil species are known as well.
e 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.
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Metasequoia (Dawn Redwood) is a fast growing tree genus in the conifer family Cupressaceae of which Metasequoia glyptostroboides, native to the Sichuan-Hubei region of China, is the only living species. Metasequoia, along with Sequoia, Sequoiadendron and several other genera, were transferred from the Taxodiaceae family to Cupressaceae using DNA analysis. M. glyptostroboides is the only extant species in its genus, but three fossil species are known as well.
Appearance
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 40-45 m tall and 2 m trunk diameter in cultivation so far (with the potential to grow to even greater heights). The leaves are opposite, 1-3 cm long, and bright fresh green, turning a foxy red-brown in fall. The cones are globose to ovoid, 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. The pollen cones are 5-6 mm long, produced on long spikes in early spring; they are only produced on trees growing in regions with hot summers.
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 was discovered in China in Modaoxi 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.
In the late 1980s, it was discovered that many of the second generation trees in cultivation suffered from inbreeding depression (extremely low genetic variability) which could lead to increased susceptibility to disease and reproductive failure. This was because most of the trees were grown from seeds and cuttings derived from as few as three trees that the Arnold Arboretum had used as its source. More widespread seed-collecting expeditions in China in the 1990s sought to resolve this problem and restore genetic diversity to cultivated Metasequoia.
Metasequoia has proved an easy tree to grow in temperate regions, and is now widely planted as an ornamental tree. Planted specimens have already reached 25-40 m in height and 1-1.3 m in diameter, despite being in cultivation for under 60 years. This rapid rate of growth has led to consideration for using the tree in forestry plantations.
It has been discovered that Metasequoia will thrive in standing water, much like the baldcypress, and if left branched to the ground in full sun, will develop the large, contorted boles that have made it famous. Limbing at an early age will prohibit this formation later on.
Paleontology
Metasequoia redwood fossils are known from many areas in the Northern Hemisphere; over 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 (Farjon 2005). During the Paleocene-Eocene Thermal Maximum, extensive forests of Metasequoia occurred as far north as Axel Heiberg Island (northern Canada) at around 80°N latitude. 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 , it was heralded as a "living fossil".
Conservation
There remains one Dawn Redwood forest, consisting of barely 5,000 trees. Since its discovery, the Dawn Redwood has become something of a national point of pride, and it is both protected under Chinese law and planted widely. As such, it's not likely to go extinct, but Dawn Redwood is critically endangered in the wild. Though cutting of trees or branches is illegal, the demand for seedlings drives cone collection to the point that natural reproduction is no longer occurring in the dawn redwood forest. Although the species will continue to live in yards, parks and on roadsides all over China, the Metasequoia forest ecosystem could disappear when its mature trees die.
In the UK
The Dawn Redwood can be found in some gardens of mansion houses and historic buildings. Bank Hall in Bretherton has two Dawn Redwoods believed to have been brought over many years ago from China and are now under conservation protection. They are thought to have possibly been a present to one of the families that lived at the hall from Kew Gardens in London.
See also
Further reading
External links
- giant redwoods in the U.K.
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