Metasequoia glyptostroboides, the dawn redwood, is a fast-growing, endangered deciduous conifer. It is the sole living species of the genus Metasequoia, one of three genera in the subfamily Sequoioideae of the family Cupressaceae. It now survives in the wild only in wet lower slopes and montane river and stream valleys in the border region of Hubei and Hunan provinces and Chongqing municipality in south-central China, notably in Lichuan county in Hubei. Although the shortest of the redwoods, it can grow to 167 ft (51 m) in height.
In 1941, the genus Metasequoia was reported by paleobotanist Shigeru Miki as a widely distributed extinct genus based on fossils, before attracting considerable attention a few years later when small populations were found alive in central China. It is a well-known example of a living fossil species. Modern dawn redwood appears identical to its late Cretaceous ancestors. The tree faces considerable risks of extinction in its wild range due to deforestation; however, it has been planted extensively in arboreta worldwide, where it has proved a popular and fast-growing ornamental plant. If the species had not been discovered when it was, it might have become extinct before being investigated.
History
Although it was commonly known from the fossil record from across the northern hemisphere, the dawn redwood was considered extinct until the mid-twentieth century. When the genus Metasequoia was first described in 1941, it was from Mesozoic Era fossils, none of which were less than 150 million years old. While studying fossil samples of the family Cupressaceae, Dr. Shigeru Miki from Kyoto University identified a divergent leaf form. He realized he had discovered a new genus, which he named Metasequoia, meaning "like a sequoia". In the same year, Kan Duo (Toh Kan, 1903–1961), professor of Forest Management, National Central University, Chongqing, (formerly Chungking) observed an enormous living specimen while performing a survey in Sichuan and Hubei provinces. Though unaware of Miki's new genus, he recognized the unique traits of the tree. Unfortunately, while he collected some plant material, he did not attempt to identify or publish his findings. This tree formed part of a local shrine, where villagers called it 水杉 (Shuǐshān or "water fir"). Shuǐshān continues to be the common name of dawn redwood in Chinese. In 1943, Wang Zhan (Chan Wang, 1911–2000) of the National Bureau of Forest Research, the Ministry of Agriculture and Forests, Chongqing, collected samples from an unidentified tree in the village of Moudao (formerly Motaochi, Maodaoqi or Modaoxi) in Lichuan County, Hubei province—now believed to be the same tree Kan discovered. The samples were determined to belong to a tree yet unknown to science, but World War II postponed further study. Professors Zheng Wanjun (Cheng Wan-Chun) and Hu Xiansu (Hu Hsen-Hsu) made the pivotal connection between Miki's fossil genus and the living samples in 1946. The name Metasequoia viva was initially used, but was eventually changed to the specific epithet "glyptostroboides", after its resemblance to the Chinese swamp cypress (Glyptostrobus). In July 1947, the Arnold Arboretum of Harvard University provided $250 to fund an expedition by Zheng Wanjun's assistant Hua Jingchan (Ching-Shan Hwa 1921–present) to collect seeds for the arboretum from the Metasequoia type tree in Moudao, and trees in the nearby Metasequoia Valley (Shuishaba Valley). Hua's collecting trip returned with several kilos of seed that were distributed over the next few months for growth trials to Chinese institutions, the Arnold Arboretum, Missouri Botanic Garden, and elsewhere in the United States, botanic gardens at Kew, Edinburgh, and other locations in the United Kingdom; as well as botanic gardens in continental Europe and worldwide.
Description
Metasequoia glyptostroboides leaves are opposite, 1–3 cm (0.39–1.18 in) long, and bright fresh green, turning a foxy reddish brown in autumn. The pollen cones are 5–6 mm (0.20–0.24 in) long, produced on long spikes in early spring; they are produced only on trees growing in regions with hot summers. The cones are globose to ovoid, 1.5–2.5 cm (0.59–0.98 in) 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. While the bark and foliage are similar to another closely related genus of redwoods, Sequoia, M. glyptostroboides differs from the coast redwood in that it is deciduous, like Taxodium distichum (bald cypress). Similar to T. distichum, older trees may form wide buttresses on the lower trunk. M. glyptostroboides is a fast-growing tree, exceeding 35 m (115 ft) in height and 1 m (3.3 ft) in trunk diameter by the age of 50, in cultivation (with the potential to grow to even greater dimensions). The trunk forms a distinctive "armpit" under each branch. The bark is vertically fissured and tends to exfoliate in ribbon-like strips. The largest dawn redwood recorded was an isolated specimen in China about 50 meters (160 feet) tall and 2.2 meters (7.2 feet) wide. This tree was killed by a lightning strike in 1951. Several dawn redwoods of this height still live in the eastern part of Metasequoia Valley, where the tree was discovered. The tree's true potential size is much larger, as logs up to 8 meters (26 feet) wide at the base have been discovered in rice paddies. The thickest and tallest dawn redwoods listed by Monumental Trees are both at Longwood Gardens, outside Kennett Square, Pennsylvania, United States. The widest has a girth at breast height of 5.79 m (19.0 ft), average diameter 1.84 m (6.0 ft), and is 30.18 m (99.0 ft) tall. The tallest is 41.15 m (135.0 ft) tall, and has a girth at breast height of 3.35 m (11.0 ft), average diameter 1.07 m (3.5 ft). Both trees were planted in 1948 and measured in 2018.
Ecotypic variation Ecotypic variation has developed in a variety of microhabitats. Three variations have been observed based on the size of their cones, large, medium, and small. The large cone type is found growing on mountain slopes, develops a broad canopy, seeds more readily and is more drought tolerant. The small cone type is found near stream banks, is more sensitive to drought, and develops a more uniform trunk.
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