Metasequoia
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| Metasequoia glyptostroboides Hu & Cheng |
Metasequoia glyptostroboides (Dawn Redwood) is a fast growing tree in the conifer family Cupressaceae native to the Sichuan-Hubei region of China. It is the only living species in the genus Metasequoia, but three fossil species are known.
While the bark and foliage are similar to the related genus Sequoia, Metasequoia differs in that it is deciduous like Taxodium distichum (Bald Cypress), and like that, 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 Cheng Wan Chun 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.
[edit] Prehistory
Metasequoia fossils are known from many areas in the Northern Hemisphere; over 20 fossil species have been named, but are now treated in 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 also make up the major portion of Tertiary fossil plant material in the badlands of western North Dakota in the United States.
[edit] References
- Conifer Specialist Group (1998). Metasequoia glyptostroboides. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 06 May 2006. Listed as Critically Endangered (CR A1c, C2a v2.3)
- Metasequoia Glyptostroboides (TSN 505864). Integrated Taxonomic Information System. Accessed on September 25, 2006.
- Farjon, A. (2005). Monograph of Cupressaceae and Sciadopitys. Royal Botanic Gardens, Kew. ISBN 1842460684.
- Metasequoia stumps, Axel Heiberg Island (pdf file)
- Jahren, A. H. & Sternberg, L. S. L. (2003). Humidity estimate for the middle Eocene Arctic rain forest. Geology May 2003 pdf file
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