Based on new census surveys recently performed by local government representatives, as well as two complementary and expanded expeditions conducted in 1997 and 2004, we present an updated database of the distribution of known native Metasequoia glyptostroboides trees in an area formed by western Hubei, eastern Chongqing, and northern Hunan in south-central China. The area is located between longitudes 108°20′E (Huangshui Town, Shizhu County, Chongqing) and 109°40′E (Tani Township, Longshan County, Hunan) and 30°10′N (Jiannan Town and Moudao Town, Lichun City, Hubei) and latitudes 29°10′N (Luota Township, Longshan County, Hunan). A total of 5396 native Metasequoia trees exist either as scattered (isolated) individual trees or in populations from two regions of this area. The majority of trees (5391 trees) grow in the first region, which includes eastern Chongqing and western Hubei. Only five trees exist in the second region at western Hunan. The database provides an updated census for the current status of living Metasequoia and a basis for further scientific research and better conservation strategies. Additionally, for the convenience of non-Chinese speakers, we have summarized the historical conservation process of this species and clarified changes in the geographic names and the structure of the Chinese administrative systems.

Since the first seeds were sent from China in December 1947, the famous “living fossil” Metasequoia glyptostroboides Hu & Cheng has been cultivated for 60 years throughout the world. The comprehensive survey of Metasequoia cultivation presented herein has been conducted over the past five years, yielding 2535 accessions from nearly 50 countries on every continent. Optimal growth seems to be in the USDA Plant Hardiness Zones 5 through 9 in North America and Europe, as well as comparable areas in East Asia. The tallest individual reported is approximately 38 m in height, and the largest is approximately 6.2 m in girth. The details of each accession are summarized, including place cultivated, recent growth statistics, and information about the source of introduction.

Shoots and branches of Metasequoia have proven notoriously difficult to preserve in herbarium collections because of the abscission of the needles on drying. In the course of preparing an exhibit, the Yale Peabody Museum of Natural History's Division of Paleobotany successfully maintained a nearly ripe seed cone of Araucaria intact during the drying process by introducing glycerol into its tissues. Like Metasequoia, ripe araucarian cones also disintegrate within a few weeks of drying. We decided to try this same preservation method on fresh-cut branches of Metasequoia. In September 2004, three shoots from a mature Metasequoia tree on the Yale Peabody Museum grounds were immediately photographed, wrapped in dampened paper towels and refrigerated for three days. Afterward, the shoots were soaked in a solution of ethanol and deionized water (95:5) for five hours, then immersed in a solution of glycerol and deionized water (50:50) for 11 days and placed in a drying oven for three months at 30 °C. On removal from the oven, the shoots were allowed to cure at a temperature of 17 °C and a relative humidity of 9% for approximately three months. The shoots were then mounted on herbarium sheets as normal and accessioned into the Yale Peabody Museum herbarium. After nearly three years, the foliage sprays are still intact and show no signs of deterioration.

This paper examines the role played by the Arnold Arboretum of Harvard University in training the first generation of modern Chinese botanists and supporting them to do field work and develop herbarium collections in China. It highlights the scientific career of H.H. Hu, who received his doctorate from Harvard University in 1925 and was strongly influenced by Arnold Arboretum staff members, including C.S. Sargent, Alfred Rehder, J.G. Jack and E.D. Merrill. The paper discusses the role of the Arnold Arboretum in the initial, worldwide distribution of Metasequoia glyptostroboides seed in 1948, and features photographs and measurements of notable specimens growing at the Arboretum today.

During the early Tertiary, the genus Metasequoia was widely distributed and abundant in the high Arctic, suggestive of an adaptive fit between the Arctic paleoenvironment and the physiology of this relic genus. While present day temperature is clearly restrictive for growth in the Arctic, evidence suggests that the paleotemperature was much more benign. In contrast, the light regime can be assumed unchanged, with annual periods of several months of continuous light and continuous darkness at the high latitudes influencing the plants that populated its paleolandscape. Previously, we have shown that the continuous-light environment is stressful for plant photosynthesis and related metabolic pathways. Here we explore the photosynthetic response along with carbon and nutrient allocation of Metasequoia glyptostroboides, Taxodium distichum and Sequoia sempervirens when exposed to a continuous-light treatment. Our findings indicate that Metasequoia has the unique combination of indeterminate growth and deciduous habit that may have been the key adaptations for the paleoarctic. Taxodium, a deciduous species with indeterminate growth, fails to develop a strong carbon sink and, therefore, suffers from photosynthetic inhibition by end-product accumulation. The absence of Sequoia (a close relative of Metasequoia) in the paleoarctic can best be attributed to its nondeciduous habit, possibly compounded by calcium or other nutrient deficiencies.

Fossils of Metasequoia, beginning in the Cretaceous Period, have been found throughout the Northern Hemisphere. In North America this genus survived at least through the Pliocene, and in Asia through the early Pleistocene. Fossils from the Holocene are missing on both continents, yet Metasequoia survived, presumably in wet-site refugia along the Yangtze River, and survives today as relic populations in central China. Metasequoia has completely disappeared in North America. We present the case that the ecological requirement of moist bare soil for seedling establishment constrains Metasequoia to regularly disturbed riparian zones. The river systems of the western United States could have provided migratory routes for Metasequoia to the Southeast as climate cooled and land masses rose. However, Taxodium, a genus not found in Asia, has the same specialized seedling establishment requirements as Metasequoia. We previously showed that Metasequoia has the superior photosynthetic system for adapting to the weak, continuous light of the high latitudes. But at the lower latitudes of the US Southeast, the photosynthetic system of Taxodium has the competitive edge. We suggest, therefore, that in North America Taxodium preempted the sites that could have been occupied by Metasequoia, eventually leading to its extirpation.

Changes in phytogeographical pattern of the Metasequoia fossil record correspond to global paleoecology and paleoclimate since Late Cretaceous times. Genetic and morphological studies of the living representatives of Metasequoia have further elucidated the evolutionary dynamics of the genus. In a continuing effort to integrate paleobotanical studies with the systematics and phytogeography of modern Metasequoia (the species M. glyptostroboides, in China), we have computerized the fossil database and used a geographic information system to untangle lines of evidence of the evolution of Metasequoia. Using Metasequoia as an example, we show the power of this technology for integrating spatial information on fossil occurrences and their geological and environmental context. Future Metasequoia fossil reports, combined with Global Positioning System locational descriptions, can be steadily integrated into the geographic information system database and offer more information for our understanding of Metasequoia evolution. Additionally, a geographic information system database has been created, linking observations of the distribution of cultivated M. glyptostroboides trees throughout the United States, and will eventually include observations of native populations in China, as part of the ongoing effort to implement an effective Metasequoia conservation plan.

Mummified leaves of Metasequoia occidentalis (Newberry) Chaney from the middle Eocene Buchanan Lake Formation at Napartulik, Axel Heiberg Island, were examined by transmission electron microscopy to determine whether sun- and shade-type leaves could be identified. Where discernable, features related to thylakoid geometry, such as the degree of grana stacking, the number of thylakoids per granum and grana stack width, were measured. The chloroplast characteristics of M. glyptostroboides Hu & Cheng leaves have a highly significant response to light intensity such that the leaves can be characterized as sun or shade leaves based on these features, indicating that adequately preserved chloroplasts in M. occidentalis leaves can also be characterized in this manner. Using data from the response of chloroplast ultrastructure to sun and shade environments in M. glyptostroboides leaves, four classification analyses, each using different combinations of chloroplast ultrastructural features, were performed to assign adequately preserved leaves of M. occidentalis as having grown in either a sun or shade environment. The ability of the four classification methods to reliably predict whether the fossil leaves grew in sun or shade environments was tested using data from leaves of M. glyptostroboides growing in known light environments. On examining 108 sections of 36 fossil leaves, 9 leaves were found to have adequate chloroplast preservation for the purpose of classification. By the method of analysis deemed to be the most reliable, five of the nine were leaves classified as sun-type leaves and four were classified as shade types. The results further suggest that leaf senescence in M. occidentalis growing in the polar forests may have been initiated by temperature, rather than low-light conditions.

Labile biomolecules, such as carbohydrates and fatty acids, are rarely preserved in the pre-Quaternary geological record and were traditionally thought to play a nonsupportive role in the preservation of morphological structures during the process of fossilization. We document the in situ preservation of polysaccharides and cutin acids in late Paleocene–early Eocene (approximately 60 Ma) three-dimensionally preserved Metasequoia leaves from Ellesmere Island, Nunavut, in the Canadian Arctic Archipelago. In addition to abundant polysaccharides, cutin-derived fatty acids are effectively detected with a modified version of the online pyrolysis–gas chromatography/mass spectrometry technique that uses tetramethylammonium hyroxide. These biomolecules are the oldest of these types of biomolecules so far documented in the fossil record. Scanning electron microscopy observations of transverse sections of the fossil Metasequoia leaf tissues indicate a layered cuticle overlaying the epidermal cells and amorphous cell walls, suggesting these tissues are the likely sources for the preserved cutin acids and cellulose polysaccha-rides, respectively. We infer that the preservation of these chemically reactive biomolecules in these plant tissues was enhanced by both physical entrapment and chemical bonding of these labile molecules to other structural biopolymers, suggesting a significant role for these labile bio-molecules in the fossilization and preservation of three-dimensional leaf tissues.

Chemical analysis of the leaves of modern Metasequoia and other gymnosperms revealed the presence of structural polyesters, guaiacyl lignin units and polysaccharides, but no long chain recalcitrant aliphatic constituent. Analysis of Tertiary fossil Metasequoia showed the presence of polysaccharides, lignin and a long chain aliphatic polymer. Tertiary fossil conifers similarly revealed the preservation of lignin and a long chain aliphatic polymer (up to C₃₃) with limited preservation of polysaccharides. Experimental maturation of modern pine needles generated a composition with a long chain aliphatic polymer and additional phenolic compounds similar to those seen in the fossils. Experimental maturation of the structural polyester cutin and a pure model C₁₆ and C₁₈ fatty acid mixture yielded fatty acids and an aliphatic polymer less than C₂₀ suggesting that polymers greater than C₂₀ may be incorporated into the fossil macromolecule from longer-chain plant waxes. Thermochemolysis of the fossil conifer revealed fatty acids from C₁₂ to C₃₀ that also occur in internal lipids and the initial structural polyester. This suggests that the formation of the aliphatic polymer in the fossil Metasequoia may have been the result of lipid incorporation, a process likely important in the long-term preservation of gymnosperms and other organic macrofossils.

Throughout much of earth history globally warm intervals prevailed over ice age conditions. Without the constraints imposed by cold climates, forest vegetation populated high-latitude land masses. There are no modern analogs for these biomes, thus fossil remains provide information vital to understanding the structure and function of these forests. This paper reviews methods (some common in neoecology) by which forest structure, biomass and productivity can be quantified from analysis of fossil remains. Common metrics of forest structure, such as stand density, stem diameter, basal area and tree height, can be determined for most fossil forest localities using the methods described herein. When fossils are preserved as in situ forest layers (so-called fossil forests), additional analyses involving detailed stem measurement or the application of allometric regression models may yield estimates of aboveground biomass. Annual growth rates, when paired with estimates of stem wood volume production, provide an enhanced view of ecosystem energy flow. A review of published studies on polar fossil forests indicates that forest vegetation has occupied high-latitude landmasses since the Late Permian. Although these forests seem to be structurally similar to modern day forests, they differ in that they sequestered large amounts of biomass in warm polar climates. Middle Jurassic forests from New Zealand and early Cenozoic Metasequoia-dominated forests from the Canadian Arctic seem to have sequestered similar amounts of biomass despite differences in plant community taxonomic composition. The lack of dramatic differences between fossil and modern forest ecosystem structure and function may point to general constraints on forest biology that are supported by theoretical models.

Glyptostrobus Endlicher is well represented in early Early Cretaceous to Pleistocene deposits in the middle to high latitudes of North America and Eurasia. Although the taxonomy and nomenclature of the genus is complicated, the fossil record indicates Glyptostrobus was represented by a small number of species. The genus first appears in Aptian age deposits from western Canada and Greenland, and achieved a wide distribution early in its evolutionary history. Exchange of Glyptostrobus between Asia and North America occurred across the Spitsbergen and Beringian corridors, which were functional about 110 and 100 million years ago, respectively. The Late Cretaceous fossil record of Glyptostrobus shows that the genus had spread into Russia, China and the shores of the Turgai Strait. By the early Tertiary, Glyptostrobus was a prominent constituent of the polar broad-leaved deciduous forests. Paleocene age deposits across western Canada and the United States indicate the genus was present in great abundance in the lowland warm temperate and subtropical forests east of the Rocky Mountains. The broad distribution in North America and Russia during the Paleocene and Eocene indicates that Glyptostrobus grew and reproduced under a diverse range of climatic and environmental conditions, including the cold and unique lighting conditions of the polar latitudes. The presence of Glyptostrobus in Europe indicates the North Atlantic land bridges that extended between North America and Eurasia (Fennoscandia) and Europe during the early Tertiary were used. In Europe, extensive Glyptostrobus dominated swamps occupied the Central European Depression during the late Tertiary. Increasing global aridity and cooling, as well as landscape stabilization together with increasing competition for resources and habitat by representatives of the Pinaceae, seem to have forced the genus out of North America, Europe and most of Asia during the Miocene and Pliocene. In Japan, Glyptostrobus persisted until the early Pleistocene. After the early Pleistocene extinction in Japan, Glyptostrobus reappeared in southeastern China. Details of the taxonomic and biogeographic history of Glyptostrobus are examined.