"I know Metasequoia. We have a lot of them planted there." "Oh, it's endangered."

Friends living in the Yangtze River Basin have all seen Metasequoia. It is a beautiful deciduous conifer . Its leaflets are like feathers, not as hard as those of pine and cypress. In autumn, the whole tree turns into a brilliant golden color. If you are a student majoring in biology, the difference between Metasequoia and Baldcypress is almost a must-answer question when studying tree classification.

The leaflets of Metasequoia are broad, soft and opposite (left), while the leaflets of Baldcypress are alternate and thinner (right)丨Zhong Shushu; Agnieszka Kwiecień, Nova

Many people know that Metasequoia is called a "living fossil", but they don't know that behind this often-abused term is the botanical history of Metasequoia being discovered in the midst of war, as well as the turmoil of the entire world over tens of millions of years.

Rebirth from the flames of war

In the summer of 1943, Wang Zhan, the chief engineer of the Central Forestry Research Institute of the Ministry of Agriculture and Forestry, set out from Chongqing to Enshi to negotiate a plant survey in Shennongjia. When he passed Wanxian, Sichuan (now Wanzhou, Chongqing), he learned from Yang Longxing, who taught at Wanxian Agricultural College, that there was a "sacred tree" in Modao Creek (now Lichuan, Hubei).

Wang Zhan thought about it and gave up the original water route and went to Enshi by land instead. After walking for three days, he saw this huge conifer and collected a specimen on July 21, 1943. After that, Wang Zhan continued to Enshi. When he returned to Chongqing, he identified the specimen as Glyptostrobus pensilis and stored it in the specimen room.

Metasequoia forest丨Fxqf / wikimedia

When the War of Resistance Against Japanese Aggression was finally coming to an end in 1945, Wu Zhonglun, a technician from the Forestry Department of Chongqing Central University, went to the Central Forestry Experimental Institute to identify plant specimens. When he saw the "Meadow Glyptostroboides" specimen handed to him by Wang Zhan, he felt that it was different from the Metasequoia glyptostroboides, so he handed it over to Professor Zheng Wanjun of the Forestry Department of Central University at that time.

Zheng Wanjun was immediately impressed by the new species and quickly visited the Central Forestry Experimental Institute. After research, he confirmed his hypothesis of a new taxon. After the war ended in 1946, he sent his graduate student Xue Jiru to Modao Creek to collect specimens and cones of the new species. In mid-April, Zheng Wanjun sent the new gymnosperm to Hu Xianqiong, then director of the Beijing Jingsheng Biological Survey Institute.

After receiving the specimen, perhaps at some point between April 22 and May 9, Hu Xianqi suddenly remembered that in 1941, Dr. Shigeru Miki of Kyoto University in Japan had established a new fossil genus Metasequoia based on the significant morphological characteristics of small leaves opposite each other in a plant fossil similar to the North American redwood genus Sequoia. After carefully reading and studying it, with the help of his assistant Fu Shuxia, he finally determined that the morphology of this specimen was exactly the same as that of the Metasequoia fossil , and it was the living Metasequoia , today's metasequoia .

Before maturity, the cones of Metasequoia are hidden among the branches and leaves. | Meneerke bloem / wikimedia

On May 15, 1948, Hu Xianqiong and Zheng Wanjun published the article "New Metasequoia Family and Surviving Metasequoia Species", which marked the end of the study of a plant specimen that survived the brutal war and also opened a new chapter. During this period, they sent some Metasequoia seeds and specimens they collected to Dr. Ralph Works Chaney, the head of the Department of Biology at the University of California, Berkeley, Dr. Elmer Drew Merrill, the director of the Arnold Arboretum at Harvard University, and botanical gardens in Copenhagen, Denmark, and Amsterdam, the Netherlands, and donated them to more botanical gardens through Chaney.

These Metasequoia seeds, which came from the first few mother trees discovered, may have taken root and sprouted again outside of East Asia tens of millions of years later.

The same loneliness exists on both sides of the ocean

The naming of plant fossil species follows the same rules as the naming of plant extant species. Generally speaking, extant species of plants are always discovered and named first, and then scientists study and believe that some fossils and extant plants have similar structures and are from the same family, genus or species, and then name the fossils .

However, the entire discovery process and naming of Metasequoia has undergone an interesting reversal. When Shigeru Miki gave the name Metasequoia to the Metasequoia fossils based on the structure of the opposite leaflets, the world did not know that there were still living Metasequoia in the mountains of China during the war. This is one of the reasons why Metasequoia was called a "living fossil" when it was discovered.

Fossils of the genus Metasequoia are also found from time to time in China. The existing Metasequoia is almost identical to these fossil Metasequoia in terms of cones and opposite leaflets. | Wang Li/ Xishuangbanna Botanical Garden

Before the discovery of living Metasequoia, fossils of Metasequoia and Sequoia subfamily had been widely unearthed in many places from North America to East Asia. Today, the two closest relatives of wild Metasequoia are the world's tallest plant, the North American redwood, and the world's largest plant, the Giant Sequoia . Metasequoia is confined to a small mountainous area at the junction of Chongqing, Hubei, and Hunan in China; Giant Sequoia is distributed in several valleys in the Sierra Nevada Mountains in California across the Pacific Ocean that can be reached by fog; and North American redwood is distributed along the Pacific coast from northern California to southern Washington State.

Separated from each other by mountains and seas, they are the only remaining members of the entire sequoia subfamily today.

Giant sequoias and redwoods are the "giants" of the tree world | Alpsdake & Mike Murphy / wikimedia; Bernt Rostad / Flickr

The study of fossils and existing species has revealed a fact: the distribution area of ​​Metasequoia and even Sequoia subfamily plants today is much smaller than their historical distribution area. What happened?

The birth of a "living fossil"

Animals on Earth were not what they are today, and neither were plants. Combining paleoclimatology and botanical research, we can roughly paint the story of Metasequoia.

During the Late Cretaceous , 80 million years ago, the climate was warmer than it is today. During this period, the locations of the Earth's continents were similar to today, except that North and South America had not yet connected, and the Indian subcontinent had not yet collided with Eurasia. Dense coniferous forests, including sequoias, covered western North America and East Asia in the North Pacific .

At the end of the Cretaceous period 65 million years ago, an asteroid impact and a series of subsequent events wiped out non-avian dinosaurs and a large number of reptiles, ending the Mesozoic Era. But only a few million years later, the Earth became lush again. During the Paleocene to Eocene Epoch of the Cenozoic Era (about 66 million to 34 million years ago), the Earth reached the peak of the Cenozoic era of humidity and heat , and fossils of Metasequoia even appeared in the 80° north latitude area in northern Canada. There was frequent movement of plants and animals between East Asia and North America in the Northern Hemisphere. During this period, the ancestors of the North American redwood, giant sequoia, and Metasequoia genera all had genetic exchanges, forming a complex network relationship.

Young leaves of Metasequoia丨Crusier / wikimedia

By the end of the Oligocene (about 26 to 23 million years ago), the warm era ended, and a period of 400,000 years of drastic cooling was followed by temperature fluctuations. Entering the ice age after the Miocene, the polar glaciers extended on a large scale, destroying large areas of once dense forests like a knife . The continuous distribution of animals and plants between East Asia and North America was also forced to end at this time.

The collision of the Eurasian and Indian plates gave rise to the majestic Himalayas and a series of east-west mountain ranges. These large-scale mountains have blocked the southward glaciers to a certain extent, providing a "refuge" for animals and plants from southern China to the Indochina Peninsula. The "relict plants" we are familiar with, such as Metasequoia, Cathaya, Davidia involucrata, and Liriodendron, are all surviving lives in the refuge.

The North American continent is squeezed by the Pacific Plate, and most of the mountains are north-south. In the central part of North America, there are no mountains to block the glaciers, and the forests are destroyed - this is one of the reasons why the diversity of plants in North America is lower than that in Asia at the same latitude. However, the movement of glaciers also grinds the rock layers, creating the fertile soil in the central part of North America today, but this is a later story.

Davidia involucrata, also known as the "pigeon tree", is a relict plant unique to China | Manfred Brückels

After the Quaternary glacial movement, that is, in the strata after the Miocene, no fossils of the genus Metasequoia have been found . So much so that when Shigeru Miki named the genus Metasequoia, scientists believed that they had long been extinct and existed only in fossils.

Although the geological story in North America may be more severe, similar refuges have been formed west of the Sierra Nevada Mountains and southern Appalachian Mountains in North America, where plants such as giant sequoias, redwoods, tulip trees, magnolias and anises have been preserved and, together with their relatives in East Asia, interpret another story that fascinates biogeography researchers - the North American-East Asian discontinuous distribution of species.

By now, you may understand the sensation caused by the rediscovery of Metasequoia in the world - it is not only a life that seems to be reborn from a fossil, but also a witness to a magnificent geological history . Therefore, Metasequoia has become a valuable gift from China on many occasions. In October 1988, Academician Wu Zhengyi of the Kunming Institute of Botany, Chinese Academy of Sciences and Academician Peter Raven of the Missouri Botanical Garden, USA, signed a cooperation agreement on the compilation of the Flora of China (English Edition) on behalf of both China and the United States, and planted a Metasequoia in the Missouri Botanical Garden.

Nowadays, Metasequoia is planted in many places in the world丨Soseipapa / wikimedia

No danger of extinction

Although Metasequoia has nominally received various national-level protections since its rediscovery, Metasequoia is listed along with Ginkgo, Davidia involucrata, and Abies dasyphylla in the "National Key Protected Wild Plant List (First Batch)" promulgated by the State Council in 1999, which has legal significance, the future of wild Metasequoia populations is not optimistic .

You may wonder, there are dozens of Metasequoia trees in the park near my home, why is it still an endangered plant?

Here we need to clarify some facts: cultivated plants cannot replace wild populations , and they often do not represent the genetic diversity of wild plant populations; many introduced cultivated plants come from only a few wild individuals, and there is widespread gene loss during the breeding process . It is common for wild populations to be endangered even though they are widely cultivated and raised, and Metasequoia is one of them.

The cones of Metasequoia are smaller than quail eggs, and the seeds are as light as fine sand丨Ge Binjie

Plant conservation by introducing plants outside their original production areas is called ex situ conservation. A complete and effective ex situ conservation strategy for endangered plants requires recording the source of collected seeds and systematically regulating population recovery steps to maintain the genetic diversity of the population. However, in the 1970s to 1990s, large-scale planting of Metasequoia for the purpose of afforestation and forestry production did not take these into account.

Although there are millions of Metasequoia trees cultivated worldwide as urban street trees and greening plants, the sources of these Metasequoia trees are relatively single , and they generally have problems such as low fruit set rate, low seed embryo development rate, and low seed germination rate, making them unable to be effectively continued.

Today, there are about 5,000 wild Metasequoia trees in their native habitat . Most of them have been severely disturbed by human activities in the past 100 years and have been cut down for firewood and building materials. In 1974, the People's Government of Lichuan County set up a dedicated agency in a small river where the original Metasequoia trees are concentrated, and established the "Lichuan County Metasequoia Management Station", which is now the "Lichuan City Metasequoia Mother Tree Management Station". In addition, in areas where wild Metasequoia trees are concentrated, Hunan established the Hunan Longshan Luota Nature Reserve, and Chongqing established the Shizhu County Huangshui National Forest Park. Frontline conservation workers have made arduous efforts to protect wild Metasequoia trees.

Although individual Metasequoia trees are protected, excessive seed collection and grazing still hinder the natural regeneration of its population because there are very few new Metasequoia seedlings.

Metasequoia trees beside a city road | Paulitzer / wikimedia

The existing wild Metasequoia populations mostly grow in valleys that are difficult for humans to reach. During his research, Dr. Yang Yongchuan found that in many flat living areas, people often dug up thick Metasequoia roots left over from past logging when they were farming and building houses. Combined with the strong vitality of cultivated Metasequoia, this may indicate that after the end of the ice age, Metasequoia was once again spread across the middle reaches of the Yangtze River, but human interference and climate change have pushed them back to an endangered state.

There is hope for the recovery of Metasequoia. In addition to protecting the original habitat and reducing disturbance , ex situ conservation is still an effective way for plants. The Metasequoia forests planted around the world have at least ensured that Metasequoia as a species is not in danger of extinction for the time being.

Far away from its native place, the Metasequoia has also demonstrated its extremely tenacious ability to survive. From Fairbanks in Alaska, USA, where the temperature reaches -40℃ in winter, to Queensland, Australia, Metasequoia can be found growing and spreading - they are lucky and tenacious creatures.

Metasequoia leaves turning red and yellow丨S. Rae / flickr

Author: Uncle Zhong

This article comes from GuokrNature (ID: GuokrNature)

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