There is only one tree left in the world. What tree is it?

Audit expert: Shen Tingting

PhD in Botany

There is a very rare plant on Mount Putuo in Zhejiang Province - the Putuo Carpinus . Currently, there is only one wild individual of this species left in the world, located to the west of Huiji Temple on Mount Putuo. Therefore, it is called "the only child of the earth" and is listed as a critically endangered tree species by the World Conservation Union.

So why is there only this one wild hornbeam left? How can we save it?

What does Putuo hornbeam look like?

In May 1930, Professor Zhong Guanxue, a famous plant taxonomist in China, first discovered the tree on Mount Putuo. In 1932, Professor Zheng Wanjun, a forest scientist, identified it as a deciduous tree of the genus Carpinus in the family Betulaceae. As it is a unique plant on Mount Putuo , it was named Carpinus putoensis. The only remaining tree is about 200 years old, about 12.8 meters tall, and has a trunk diameter of about 63.7 cm.

Source of the mother plant of Putuo Carpinus next to Huiji Temple on Putuo Mountain｜Wikipedia

The bark of Putuo hornbeam is blue-gray, the leaves are dark green, and the leaf edges have irregular, hair-like, double serrations; the male and female flowers are dioecious, and it blooms every spring. The female and male flowers are light red and light yellow respectively, and the fruits mature in late September and early October; the infructescence is 3 to 8 cm long, with 4 to 8 pairs of fruit bracts, and the fruits are broadly oval.

Fruit bud source｜Xiaoxiang Morning News

According to records, there were more than one Putuo hornbeam tree on Putuo Mountain in the 1950s. So, what caused it to become endangered?

Why is the Putuo hornbeam on the brink of extinction?

Through years of observation and research, researchers have summarized the multiple reasons why the Putuo hornbeam is endangered:

First of all, it is the impact of human activities. In the 1950s and 1960s, due to deforestation and indiscriminate logging, the growth environment of Putuo hornbeam was destroyed, the number of plants in the wild was decreasing, and after the plants were cut down, it was difficult to sprout and regenerate, which directly caused Putuo hornbeam to be endangered.

Secondly, this is related to its own reproductive mechanism. On the one hand, the male inflorescences are evenly distributed in the upper, middle and lower parts of the crown, while the female inflorescences are concentrated in the upper and middle parts of the crown, making the pollination efficiency low. The pollen of Putuo Carpinus relies on wind power to spread, but it often encounters rain and strong winds during the flowering period, which greatly hinders the male flower pollen shedding and pollen spread.

Source｜Photographed by Liu Jun from China Plant Image Library

To make matters worse, the flowering times of the female and male flowers of the Putuo hornbeam are inconsistent , and their open period only lasts about 9 days, resulting in a very short pollination period.

Moreover, the vitality of the pollen is relatively low. Studies have shown that the pollen germination rate of native mother trees is less than 30.8%, and its survival time at normal temperature is only 7 to 12 days, which greatly reduces the chance of successful pollination.

The origin of the seeds of Carpinus pueraria in Putuo｜Photographed by Li Yao from the China Plant Image Library

On the other hand, the seed quality is poor, the plumpness rate is very low, and the seed shell is thick and hard, with poor water and air permeability, resulting in a very low germination rate. In addition, affected by bad weather such as typhoons, it is easy for flowers and fruits to fall, making the reproduction of Putuo hornbeam even more difficult.

Many parties work together to save the Putuo hornbeam

The earth is a huge ecosystem where various species influence and depend on each other. If species continue to disappear, it will eventually affect every life.

Therefore, it is very important to rescue and protect the Putuo hornbeam. The main protection methods include in situ preservation, ex situ preservation, artificial assisted pollination, artificial sowing and cutting propagation.

Mount Putuo is now designated as a national key natural scenic area. The management bureau has effectively protected the mother tree of Putuo hornbeam by building retaining walls, setting up publicity and protection monuments and other protective measures.

Source of the publicity and protection monument｜NetEase

Botanists and foresters have conducted research on asexual reproduction techniques such as sowing, cuttings, and grafting, as well as sexual reproduction such as low-temperature cold-storage of pollen, artificial pollination, and seed stratification vernalization. They have also collected seeds from native mother trees to cultivate seedlings and established artificial offspring population protection forests. After years of hard work, there are now more than 10,000 Putuo hornbeam offspring seedlings that have been successfully bred, effectively alleviating the endangered status of this tree species.

Source: Baidu Encyclopedia

In 2011, Tiangong-1 also sent seeds of the Putuo hornbeam into space for a space breeding experiment , which is of great significance to enriching the genetic diversity of the hornbeam. Because most of the seedlings now are descendants or clones of the "only son of the earth", they are seriously lacking in genetic diversity, which also makes it still vulnerable.

Although the Putuo hornbeam is temporarily out of danger of extinction, it is rare to collect seeds that can germinate from artificially cultivated seedlings. If the Putuo hornbeam cannot achieve self-renewal and maintenance, then it cannot completely get rid of the endangered status.

In the future, scientists will continue to conduct research, especially on sexual reproduction technology, such as improving the pollination ability of pollen, increasing the quantity and quality of seeds, so that they can germinate and renew seedlings under natural conditions.

The former "only child of the earth" is no longer alone. It not only continues to reproduce in Putuo Mountain, but has also been introduced to other areas. If you travel to Putuo Mountain, you might as well take a look at this luxuriant century-old mother tree.