Metasequoia

Metasequoia (Metasequoia glyptostroboides), or dawn redwood, is a fast-growing deciduous tree, one of three species of conifers known as redwoods, and the sole living species in its genus. It is native to Lichuan county in Hubei province, China. Although the shortest of the redwoods, it grows to at least 165 feet (50 meters) in height. Local villagers refer to the original tree from which most others derive as Shui-shan (水杉）, or "water fir", which is part of a local shrine. Since its rediscovery in 1944, the dawn redwood has become a popular ornamental, with examples found in various parks in a variety of countries.

This article is about the redwood genus, Metasequoia. For the software, see Metasequoia (software).

Metasequoia
Temporal range: Late Cretaceous - Recent
Scientific classification
Kingdom: Plantae
Clade: Tracheophytes
Division: Pinophyta
Class: Pinopsida
Order: Pinales
Family: Cupressaceae
Subfamily: Sequoioideae
Genus: Metasequoia
Miki
Species

Together with Sequoia sempervirens (coast redwood) and Sequoiadendron giganteum (giant sequoia) of California, Metasequoia is classified in the Cupressaceae subfamily Sequoioideae. M. glyptostroboides is the only living species in its genus, but three fossil species are known. Sequoioideae and several other genera have been transferred from the former family Taxodiaceae to Cupressaceae based on DNA analysis.[1]

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.[2] Fossils are known from the Cenomanian onwards. 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.[3] 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 trait evolved in response to the unusual light availability patterns, not to major seasonal variations in temperature.[4] 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 trait occurred before colonizing the high latitudes and was the reason Metasequoia was dominant in the north.[5]

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".

Appearance
Dawn redwood foliage - note opposite arrangement

The bark and foliage are similar to Sequoia, but Metasequoia is deciduous like Taxodium distichum (bald cypress), and, similarly, 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 even higher).

The leaves are opposite, 0.4-1.25 inches (1–3 cm) long, and bright fresh green, turning 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 has experienced morphological stasis for the past 65 million years: the modern Metasequoia glyptostroboides appears identical to its late Cretaceous ancestors.[6]

History
Eocene (Ypresian) age M. occidentalis branchlet

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[7]) 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.[7] A few trees are also said to exist in neighboring Hunan Province.[7]

Metasequoia in gardens, parks and streets

Dawn redwoods are fast-growing trees. They sometimes grow too large in smaller gardens under favorable conditions, but they can be a good choice for a wide range of larger gardens and parks. Although they live in wet sites in their native habitat they will also tolerate dry soils.[8] Unlike most conifers, their deciduous habit means they do not cast too much shade in winter. They are grown as street trees in London and elsewhere.

Strawberry Fields is a landscaped section in New York City's Central Park dedicated to Beatle John Lennon. At the northern end of the lawns are three dawn redwood trees. The trees drop their needles each fall and regrow them each spring, a symbol of eternal renewal. The trees are expected to reach a height of 36 meters (118 ft), making them visible from great distances.

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References
  1. Paul A. Gadek; Deryn L. Alpers; Margaret M. Heslewood; Christopher J. Quinn (2000). "Relationships within Cupressaceae sensu lato: a combined morphological and molecular approach". American Journal of Botany. 87 (7): 1044–1057. doi:10.2307/2657004. JSTOR 2657004. PMID 10898782.
  2. A. Farjon (2005). Monograph of Cupressaceae and Sciadopitys. Royal Botanic Gardens, Kew. ISBN 1-84246-068-4.
  3. Christopher J. Williams; Arthur H. Johnson; Ben A. LePage; David R. Vann; Tatsuo Sweda (2003). "Reconstruction of Tertiary Metasequoia forests. II. Structure, biomass, and productivity of Eocene floodplain forests in the Canadian Arctic" (PDF). Paleobiology. 29 (2): 271–292. doi:10.1666/0094-8373(2003)029<0271:ROTMFI>2.0.CO;2.
  4. Ralph W. Chaney (1948). "The bearing of the living Metasequoia on problems of Tertiary paleobotany". Proceedings of the National Academy of Sciences. 34 (11): 503–515. Bibcode:1948PNAS...34..503C. doi:10.1073/pnas.34.11.503. JSTOR 88221. PMC 1079159. PMID 16588827.
  5. Richard Jagels & Maria A. Equiza (2005). Competitive advantages of Metasequoia in warm high latitudes. pp. 335–349. In LePage et al (2005).
  6. Ben A. LePage, Hong Yang & Midori Matsumoto (2005). The evolution and biogeographic history of Metasequoia. pp. 3–115. In LePage et al (2005).
  7. Gaytha A. Langlois (2005). A conservation plan for Metasequoia in China. pp. 367–418. ISBN 9781402026317. In LePage et al (2005).
  8. B.G. Hibberd, ed. (1989). Urban Forestry Practice, Forestry Commission Handbook 5. p. 61. In Hibberd (1989).

Further reading
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