The innocent-looking little white flower is actually a hidden "plant bulldozer"

I believe that everyone has seen this kind of white flower in childhood. It blooms all over the mountains and plains in wastelands by the roadside, in fields, in front of and behind houses. It is fresh and elegant and is often mistaken for a "daisy". In fact, its real name is "Erigeron annuus".

Small white flowers commonly seen on the roadside/Photo by Yang Xinai

People always sing praises to the tenacious vitality of annual fleabane, but did you know that it, which blooms on the ridges of fields, is a malignant invasive alien plant?

Understanding annual grass: a stranger from a foreign land across the ocean

Fleur dessert belongs to the genus Erigeron of the Asteraceae family and is native to North America. The hometown of Fleur dessert is separated from China by the natural barrier of the Pacific Ocean. How did it come to China across the vast ocean?

The annual grass is just as its name suggests. It grows in early summer and dies in late autumn. It can only survive for one year. Source: Flora of China

Some of them were accidentally brought onto ships and entered Chinese soil with ocean-going ships, and some spread naturally from neighboring countries that were also invaded by annual weeds. These "strangers" came to Chinese soil and made their home here.

According to records, the annual sedge was first collected in Shanghai in 1886, and then began to spread slowly in China. In the following years, the annual sedge gradually adapted to the local climate and environment of China, gradually established a stable population in East China, and temporarily lived in peace with its local plant "neighbors".

But I never thought that this inconspicuous "foreigner" actually had the "wolf ambition" to overthrow the local plant dynasty and seize territory to establish itself as the king. The comfortable life in East China alone could not satisfy the ever-expanding desire of the annual sedge.

44 years later, in 1930, the annual sedge entered a rapid spread stage in my country. Starting from the East China region, it expanded wildly in all directions, fighting its way out of the siege of native plants, expanding its territory, and gradually established its own "dynasty". To this day, the annual sedge can be seen in most parts of my country.

Ecological destruction: serious invasive species

In 2014, my country included annual sedge in the "List of Alien Invasive Species in China (Third Batch)". The so-called alien invasive species refers to species that appear outside the past and current natural distribution range, have formed self-regeneration capabilities in local natural or semi-natural ecosystems or habitats, and cause obvious damage or impact to local ecosystems or landscapes, that is, foreign species with strong reproductive capacity that destroy the local ecology.

In the "List of Invasive Plants in China", annual sedge is classified as a first-level, malignant invasive plant, that is, a species that has caused huge losses and serious impacts on economic or ecological benefits at the national level, and the invasion range exceeds more than one natural geographical area. Annual sedge is an alien invasive species with a wide distribution and serious damage in my country. Annual sedge occurs in large quantities and spreads rapidly, often harming economic crops such as wheat and fruit trees, mulberry and tea, and also invades grasslands, pastures, and nurseries, causing damage to the soil environment. It can be seen how serious the damage caused by annual sedge in my country is.

Another malignant invasive plant is the notorious Canada goldenrod. Speaking of this well-known invasive plant, our impression of Canada goldenrod is that it is tall, densely grown, and tyrannically occupies the entire area, appearing in various places such as roadsides, fields, and under forests.

What has it taken for this tiny wildflower to earn itself a place on the list of invasive plants, alongside water hyacinth and Canada goldenrod?

Let's break down the invasion strategy of the vicious invasive plant, Fleur des Annuus, step by step.

Invasion strategy: "growing a large population" and enduring hunger and thirst

When talking about invasive plants, we have to mention their reproductive ability. Strong reproductive ability can be said to be a "compulsory course" for every invasive plant, and annual fleabane is of course no exception.

First of all, from the perspective of "hardware facilities", like other Asteraceae plants, the "flower" we see is actually a head inflorescence composed of many flowers of different shapes gathered together. Each "petal" on the outside and the "flower center" in the center are completely independent flowers of the annual sedge. Unexpectedly, it is very different from the "flower" we usually know.

Each "flower" is a capitulum/Photo by Yang Xinai

The flowers on the outside that look like "petals" are called ligulate flowers. They have abandoned their fruit-bearing function and become sterile flowers. Instead, they are responsible for "attracting bees and butterflies", making the annual holly conspicuous and visible to insects at a glance, increasing the probability of insects visiting the annual holly. The yellow "flower heart" on the inside is formed by several tubular flowers gathered together, which can provide pollen, is a fertile flower, and is also the "main force" of annual holly fruiting and seed production.

When insects land on the flower heads of annual hollyhocks to suck nectar and chew pollen, they also get pollen from annual hollyhocks on their bodies. When insects travel back and forth between different annual hollyhocks, they also unintentionally help the annual hollyhocks complete pollination. .0

The successful pollination of fertile flowers means the birth of seeds. The fruit-setting rate of annual hollyhock is very high, and the number of fruits and seeds produced is almost the same as the number of tubular flowers on the capitula. The "seedlings" of annual hollyhock are very prosperous. One annual hollyhock can produce more than 40,000 seeds per year. Although the germination rate of annual hollyhock seeds is less than 5.08%, the number of seeds is so large that one annual hollyhock can germinate about 2,000 seeds in total. This is the breeding strategy of "winning by quantity".

Of course, annual hollyhocks are not only responsible for producing seeds, but also for how to spread the seeds far away. Therefore, annual hollyhocks have equipped each seed with "equipment" for hiking. The seeds have white pappus, like the "parachute" of dandelions. In addition, annual hollyhocks are very light. When the wind blows, these 2,000 seeds will prop up the "parachute" and fly far away on the wind, acting as the "vanguard" to further expand the distribution range of annual hollyhocks.

What’s even more frightening is that the annual sedge has set a very short germination “program” for its seeds, and mature seeds can germinate as soon as they fall to the ground, so the annual sedge has become an “annual sedge” that can be seen most of the year. Even though the seeds still face many challenges after germination and may die, the number that can eventually survive and grow into plants should not be underestimated.

The strong reproductive ability is the basic skill that makes annual ragweed one of the malignant invasive plants, and its strong survival ability is also the "basic quality" of it as a malignant invasive plant.

One year sedge can endure hunger and thirst, and has a very strong vitality. One year sedge blooms in places that many plants cannot tolerate, such as roadsides, banks, and under forests. Even in barren wastelands, one year sedge can be seen and quickly occupied. The strong survival ability also earns One year sedge the title of "pioneer species".

Annual sedge has strong reproductive, propagation and survival abilities, and can bloom brilliantly even in harsh environments. It is precisely because many Asteraceae plants have similar characteristics to annual sedge that the Asteraceae family has prospered and become one of the largest plant families on Earth today. At the same time, the Asteraceae family is also the largest family of invasive plants in my country.

Hidden "Secrets": Allelopathy

In addition to its strong survival and reproduction capabilities, annual ragweed also has a hidden "secret" - allelopathy.

Allelopathy refers to the release of chemical substances by plants into the surrounding environment, which directly or indirectly have harmful or beneficial effects on surrounding plants. The released chemical substances are called allelopathic substances.

Annual sedge releases allelopathic substances (terpenoid compounds) into the surrounding environment, which is intended to protect itself and attract insects. However, when these allelopathic substances enter the environment, they will have allelopathic effects on surrounding plants. When the concentration of allelopathic substances is high, it will inhibit the germination and growth of other plants.

With the blessing of allelopathic action, a "chemical weapon", annual sedge can eliminate other competing plants, quickly occupy the territory, and form a densely growing population. The flourishing annual sedge on the lawn also further squeezes the living space of other plants. The allelopathic substances of annual sedge can also inhibit the germination of seeds and the growth of crops such as tomatoes, cucumbers, peppers, cabbages, and radishes. It is a very troublesome weed for farmers.

Other invasive alien plants also have allelopathic effects. For example, the top invasive alien plant, Canada goldenrod, contains a large amount of volatile terpenoid compounds. These allelopathic substances inhibit the growth of surrounding plants, making it easier for Canada goldenrod to form groups. The allelopathic substances of ragweed can change the number of soil microorganisms, destroy the land, and inhibit the germination and growth of other plants. Mikania micrantha releases allelopathic substances into the soil through its roots, inhibiting the germination and growth of seeds of other plants. Combined with its extremely strong sexual and asexual reproduction ability, it has become a global invasive plant...

Allelopathy is an important mechanism for the successful invasion of alien plants. At the same time, in the invaded areas, due to the lack of degradation factors of allelopathic substances, allelopathic effects cannot be balanced, so allelopathic substances continue to accumulate in the soil. Over time, the original physical and chemical properties of the soil are changed, and the microbial structure of the soil is also changed, making the soil in the invaded area no longer suitable for the growth of other native plants, further worsening the invasion of alien invasive plants, causing biodiversity loss, and seriously threatening my country's biological security! At present, more than 660 alien invasive species have been confirmed to invade my country's agriculture and forestry, and the direct economic losses caused each year exceed 200 billion yuan.

We are taking action to prevent biological invasions

Are we humans helpless against the rampant alien invasive plants? Of course not. In fact, there are many ways to prevent and control alien invasive plants, such as physical control, chemical control, biological control and alternative control. Biological control is divided into the introduction of natural enemy insects and the introduction of plant pathogens. What practical control methods do we have for annual sedge?

Physical prevention

Annual holly can bloom most of the year, with the peak flowering period from June to August and the fruiting period from August to October. Recently is the peak flowering and fruiting period of annual holly.

If you encounter a small amount of annual sedge, you can remove it by uprooting it. If you pull out the annual sedge that is already loose, the shaking during the pulling process will shake off the already loose seeds of the annual sedge. If a gust of wind blows at this time, the seeds of the annual sedge will be spread far away by the wind. In the fruiting period, you can first wrap the fruit sequence of the annual sedge with a bag, and then pull it out by the roots, so that the seeds will not be spread by the wind. When it is in a large area, one person's strength is limited, so you can call 12345 or contact relevant professional departments.

Chemical control

Chemical control is the most economical and effective method. Spraying herbicides such as mesotrione, glyphosate and roundup, combined with manual removal, can effectively reduce the number of annual weeds.

Although spraying herbicides is low-cost and highly efficient, the health problems caused by herbicides cannot be underestimated. For example, exposure to glyphosate may cause health hazards such as neurotoxicity, reproductive toxicity, liver toxicity, and kidney toxicity to the human body, and has certain carcinogenicity. At the same time, the residues of herbicides in the environment will also cause serious pollution problems. The long-term use of herbicides will make some weeds resistant. While herbicides reduce invasive plants, they will also indiscriminately affect other land natives that are regarded as "weeds": native plants. Chemical control is not a long-term solution after all.

Biological control

Although the current control measures for annual sedge are mainly physical and chemical control, my country has also adopted low-cost, pollution-free, non-resistant and long-lasting biological control measures to deal with other malignant invasive plants. For example, in 1984, the natural enemy of purple stem sedge, the bluefly, was introduced to Kunming; in 1990, the ragweed moth was introduced to control ragweed and three-leaved ragweed; for water hyacinth, five natural enemy insects and two pathogenic fungi with good host specificity for water hyacinth have been released in the world so far. At present, there is still a gap in the biological control of annual sedge. I believe that in the future scientists will be able to find effective and safe methods to control annual sedge.

Biological invasion is one of the most important factors causing biodiversity loss besides habitat destruction. In the current era of global economic integration and international trade development, it is a long-term and tough battle to strictly control the checkpoints, prevent the invasion of alien species and protect biodiversity, and the alarm bell for biosecurity is ringing.

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The article is produced by Science Popularization China-Creation Cultivation Program. Please indicate the source when reprinting.

Author: Yang Xinai, Shanghai Science Writers Association - Science Writer of Shanghai Normal University

Reviewer: Wang Kang, Director of the North Science Museum of the National Botanical Garden, Professor-level Senior Engineer

Source: Starry Sky Project