National Botanical Gardens Guide! This "ancient species" that has lasted for tens of millions of years is blooming now~

Audit expert: Shi Jun

Doctor of Botany, well-known popular science writer

Today, my country's first national botanical garden was officially inaugurated, housing and exhibiting a wide variety of plants. On the day of the inauguration of the National Botanical Garden, let's take a look at one of the star tree species, a first-class protected plant in my country, the legendary "Chinese Dove Tree".

Source: Weibo@National Botanical Garden

Enter the Beijing Botanical Garden from the south gate, and follow the central axis road northward to the perennial flower garden on the east side of the Reclining Buddha Temple. In the northeast corner of the garden, there are several special plants hidden in the green of the garden. They have gray-brown bark that often breaks into small pieces irregularly and broad ovate leaves with serrated edges. Every year from mid-April to around May 1st, it will bloom with white flowers all over the tree. From a distance, it looks like a tree full of hundreds of white handkerchiefs, dancing in the wind under the spring sunshine. This plant is our protagonist today, an ancient relic that has lasted for tens of millions of years - Davidia involucrata.

Source: Wikipedia

There are many first-class protected plants in China, some of which, such as Ginkgo biloba and Metasequoia glyptostroboides, have left their original wild habitats and are widely planted as street trees in cities. However, Davidia involucrata is an exception. Its habits are very similar to those of the pandas we are familiar with, so it is also called the "Giant Panda of the Plant World."

Today we will talk about the past and present of Davidia involucrata.

The Beauty of Davidia involucrata Davidia involucrata was first discovered in the remote mountain forests of Sichuan and Hubei. For the botanists who first visited it, Davidia involucrata was an extremely impressive plant, especially its beautiful flowers.

Zhang Jiaxun, a botanist in my country, once described it this way:

"The Davidia involucrata tree has a graceful and elegant posture, with broad green leaves and particularly peculiar flowers... In the early stage of flowering, the buds stand upright, with two bracts covered with a layer of yellow-green fluff, the color is duck egg blue, and the stamens are light brown, like the "head" of a pigeon. A flower is like a pigeon that has just hatched. When the two bracts grow to the middle stage, the color turns to snow blue, and when they grow to the late stage, the color turns to pure white, like a pair of wings of a white pigeon, which can sparkle in the sun... Whenever the breeze blows, the white flowers float in the green sea, like a group of pigeons dancing. When the wind stops and the trees are still, they look like a group of pigeons resting. The pure white and jade-like grace makes the viewers linger."

In the writings of Wilson, a famous "plant hunter" in the West, Davidia involucrata has this kind of grace:

"We are deeply touched by the beauty of this tree... The special beauty of Davidia involucrata lies in its two snow-white bracts that support the inflorescence... Whenever the breeze blows, it is like a large group of butterflies flying among the trees; when viewed from a distance, the white flowers partially covered by the green leaves make the whole tree look like it is decorated with snowflakes. On cloudy days, in the early morning and at dusk, its pure white buds are particularly moving... In my mind, Davidia involucrata is the most interesting and beautiful tree species in the northern temperate zone."

Source: Wilson's book "A Naturalist in Western China", Volume 2, page 43

Davidia involucrata is an ancient plant, and the earliest Davidia involucrata fossils were found in the early Tertiary period. At that time, the earth was in a period of change. Ferns had greatly decreased, and only a few members of the cycads and ginkgos among gymnosperms remained. Conifers were not as prosperous as they were in the Mesozoic Era, while woody angiosperms had achieved a lot of development. Davidia involucrata flourished during this period along with many species of the same era, and spread throughout the ancient tropical regions of the earth at that time.

As an ancient plant, Davidia involucrata has some very special features. The two white "petals" of Davidia involucrata are not petals in the morphological sense. Its real flower is actually located between the two "petals". At first glance, it looks like a small ball sandwiched between two white wings (hence the description of "Davidia involucrata flowers are shaped like young pigeons" in the previous article). If you look closely, you can see that several male flowers are clustered around a female flower (you can also see many male flowers clustered around a bisexual flower) to form a head inflorescence. The white "petals" are actually bracts growing at the base of the inflorescence.

Flowers and bracts of Davidia involucrata Source: Wikipedia

Of course, this does not mean that Davidia involucrata is the only plant with bracts. Many modern plants have bracts, but the bracts of Davidia involucrata are too easily recognizable.

Flowers and bracts in the early stages of growth Source: Wikipedia

Every year in late spring and early summer, Davidia involucrata begins to bloom. In the early stage of flowering, the two bracts of Davidia involucrata stand upright and are the same color as the leaves. After 15-20 days, the two bracts gradually grow larger and the color gradually changes to snow-blue. What's interesting is that the development speed of the two bracts will be significantly different during this period, with one bract growing faster and the other slower. During this period, the large bract can grow to 10-15cm long, while the small bract is only 4-8cm long. The two bracts are still standing upright.

However, as the bracts continue to grow and the seeds swell after fertilization, the pedicels cannot bear the weight of the bracts and seeds and are bent. The bracts droop one after another and turn white. After the two bracts droop, they continue to grow for 10-15 days. When the bracts fall off, the large bracts can grow to 10-25cm long, and the small bracts are 10-15cm long. It takes 40-50 days for a flower to grow from budding to bracts falling off. Such a long viewing time and such rich changes are rare among woody flowers.

Flowers and bracts of Davidia involucrata Source: Wikipedia

What is the function of bracts? Scientists noticed that Davidia involucrata is an insect-pollinated plant, so they speculated that the function of its bracts might be to attract insects for pollination and protect pollen from rain. As mentioned earlier, the bracts of Davidia involucrata gradually change color during their growth, so scientists used this feature to design an interesting experiment to verify the function of bracts.

They treated the bracts of Davidia involucrata in four different ways (see the figure below for details). The results showed that the frequency of insect visits to the flowers of Davidia involucrata that was made to look real with white paper was significantly higher than that of the flowers without bracts or with green bracts. This proves that the color change of the bracts of Davidia involucrata during flowering is actually to enhance the attraction to insects. Bracts have some functions similar to petals.

Four different treatment methods for Davidia involucrata bracts

Clockwise direction represents: (1) removing two bracts; (2) using artificial bracts of the same shape and size made of green paper to replace the natural bracts; (3) using artificial white bracts made of white paper to replace the natural bracts; (4) keeping the original bracts as the control group.

How did such a magical plant, Davidia involucrata, come into people's sight and into the bustling city?

The origin and legend of Davidia involucrata The process of Davidia involucrata coming into people's vision is as legendary as its unique appearance.

In April 1868, when the Davidia involucrata flowers were in bloom, Westerners observed wild Davidia involucrata for the first time in a place called Muping (now Baoxing County) in the Ya'an area in western Sichuan. The observer was a French Catholic priest, Armand David. Armand David was a naturalist with a great passion for nature. He devoted a lot of energy to collecting rare animal and plant specimens in China. At this time, he had just discovered traces of giant pandas in this dense forest not long ago, and Davidia involucrata, along with the thousands of species he discovered, were made into specimens and sent to France.

Tan Weidao Source: Wikipedia

Zoologists and botanists far away in France were sorting out the specimens sent by Tan Weidao. When a botanist named Henri Baillon saw the Davidia involucrata, he named it Davidia involucrata. The genus name Davidia is Tan Weidao's surname, and the specific epithet involucrata means "several flowers surrounded by a circle of bracts." So in 1871, the Davidia involucrata got its own exclusive name for the first time and was recognized by the Western academic community.

As the sorting work progressed, the "Tan Weidao Natural History" introducing Tan Weidao's work was published in 1888. As the only color illustration in the second volume, Davidia involucrata successfully attracted the attention and interest of Westerners, especially the British who were very enthusiastic about flower and tree gardening and the introduction of Chinese wild plants at that time. In 1899, the British Veitch Nursery Company sent a 22-year-old young man named Henry Wilson to China to collect Davidia involucrata. Wilson first visited A. Henry, who worked at the Consulate in Simao, Yunnan, and investigated his experience of seeing Davidia involucrata, and successfully obtained clues about the location of Davidia involucrata. In April 1900, after a hard journey and search, he regretfully discovered that although he had found the location of Davidia involucrata, the owner of the tree had just cut it down not long ago.

Source: Wikipedia

Fortunately, with the help of local employees, Wilson finally found the Davidia involucrata in a place called Wencao, southwest of Yichang, Hubei, on May 19, and collected branches of the Davidia involucrata covered with flowers. Wilson's wonderful description of the Davidia involucrata in the previous article was left over from this period.

However, although Wilson successfully brought the Davidia involucrata back to Europe, the initial introduction of the Davidia involucrata was not very smooth.

The shell of Davidia involucrata seeds is very hard, with poor water and air permeability, and it has a dormant period of up to 2 years in the natural state. Therefore, it is often eaten by animals or rots before normal germination, losing the ability to germinate. The germination rate in the natural state is only 3%. In 1881, Kew Botanical Gardens in the UK received Davidia involucrata seeds sent by Han Erli; after discovering Davidia involucrata, Wilson also collected a batch of seeds from Badong in Hubei and sent them to a British horticultural company for cultivation. As a result, both introductions failed. When it first arrived abroad, Davidia involucrata was not able to adapt well to the environment different from its hometown.

Source of Davidia involucrata seeds丨Wikipedia

Such performance of Davidia involucrata aroused the interest of botanists, who turned their research focus to its native environment. It turned out that Davidia involucrata grows all year round in a cool, humid, and misty deep mountain environment. It is intolerant to barrenness and drought, and cannot tolerate temperatures above 38°C. It grows poorly in dry, windy places with direct sunlight. Therefore, the cultivated forest land cannot be selected on windy, arid, and barren soils or on mountain tops, but must be selected on semi-shaded slopes or shady slopes at the bottom of the hillside, or on both sides of the valley with high humidity.

While actively improving the introduction plan, plant researchers have also become curious about the origin of Davidia involucrata. How did such a delicate and ancient plant survive through millions of years of climate change and environmental upheavals? Since the Quaternary period, the Earth has experienced dramatic climate changes, and many plants that lived at the same time as Davidia involucrata have become extinct. How did Davidia involucrata survive?

Because Davidia involucrata grows in China.

In the early Tertiary period, the earth's climate was warm and humid. Such living conditions allowed Davidia involucrata and other contemporary plant species to spread throughout the northern hemisphere. However, starting from the early Oligocene (about 3.4 million years ago), the climate gradually cooled, and these species began to gradually retreat southward to low-latitude areas. In the late Tertiary and Quaternary periods, they retreated further south to three regions: East Asia, North America, and southwestern Europe. Compared with Europe and North America, the East Asian region to which China belongs only had very limited glacier coverage during the Quaternary glacial period. In addition, the numerous mountains and canyons in southern China buffered the drastic climate fluctuations, providing a long-term stable living environment for species to remain in situ. Under the combined effect of these two factors, China has become the country with the richest and most diverse ancient plant species - the "refuge of Tertiary plants". Davidia involucrata, as a representative species, has survived and reproduced to this day.

Today, Davidia involucrata is widely planted both in China and abroad. Beijing began to introduce Davidia involucrata in the mid-1980s. In addition to the perennial flower garden of the Botanical Garden, Davidia involucrata has also been grown in Tsinghua University, the Southwest Suburbs Nursery, and the Olympic Forest Park.

In order to allow the Davidia involucrata to survive in Beijing, plant workers have thought of many ways to protect them: Davidia involucrata likes shade, and drought poses a greater threat to them than cold, so they must be watered in a timely and frequent manner, and they must also be careful to avoid excessive water accumulation and drowning. In addition, Beijing's spring is windy and dry, so in order not to damage Davidia involucrata, plant workers have built wind barriers and shade sheds for them, so that the survival rate of Davidia involucrata is guaranteed, and they are gradually growing in Beijing and blooming white flowers again.

Source: People's Daily Online

On June 18, 2016, Davidia involucrata from China traveled across the ocean to Serbia and was planted in the Belgrade Botanical Garden by Ms. Peng Liyuan and Ms. Dragica, wife of the Serbian President. On September 29, 2011, seeds of Davidia involucrata and seeds of three other rare and endangered plants (Carpinus pueraria, Parashorea chinensis, and Rhododendron dasyphylla) were launched into space along with the Tiangong-1 space station.

Initially, Davidia involucrata entered the public's field of vision as a mysterious species pursued by Western gardeners and naturalists, but now it has surpassed the original traditional impression. As a national treasure, it has become an ambassador of peace and friendship, flying across the oceans and into the universe. The Davidia involucrata planted in the city is also inspiring our belonging and love for the land under our feet with its unique beauty and legendary stories.

I hope you have time to visit the Davidia involucrata in Beijing.