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Dawn Redwood is a fast-growing tree in the
(Cypress) family
Cupressaceae, native to the
Sichuan-Hubei
region of
China. It is the only living
species in the ancient redwood
genus
Metasequoia, but three
fossil
species are known. Metasequoia, along with
Sequoia,
Sequoiadendron and several other genera, were reclassified
from the
Taxodiaceae family to Cupressaceae after DNA analysis
brcame possible.
While the bark and foliage are similar to the
closely related redwood genus
Sequoia, Metasequoia differs from the California
redwood in that it is
deciduous. 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. 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.
Metasequoia redwood fossils are known from
many areas in the Northern Hemisphere; over 20 fossil species have
been named (some are even identified as the genus Sequoia),
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 (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.
--From Wikipedia
Metasequoia |
