It's jué! A large group of "fern seeds" appeared on the beach in Shanghai!

Yesterday, a tweet saying "Shanghai's largest wild population of water ferns was discovered in Jinshan District" went viral on major news media in Shanghai and even alerted Shanghai News.

So, who exactly is the water fern? Why has it attracted so much attention? With these questions, we conducted an exclusive interview with Peng Zhi, a senior engineer at the Shanghai Forestry Station, who discovered the water fern population.

Water fern

Image source: Peng Zhi

What exactly is water fern?

Ceratopteris is an annual fern in the Ceratopterideae subfamily of the Pteridaceae family, which is suitable for growing in aquatic or wet environments. According to the Flora of China, the Ceratopteris plants distributed in my country are mainly Ceratopteris thalictroides and Ceratopteris pteridoides.

There is also a new academic view that the water fern distributed in China is the Guam water fern (C. gaudichaudii), but the authoritative view is that the Guam water fern is a synonym of the water fern.

(Synonym: The same species is given two names. If a species has multiple names, then one of them is determined to be the valid name, and the other names are synonyms accordingly.)

Water fern and thick-stemmed water fern have similarities and are often confused in the wild. However, upon closer inspection, there are obvious differences in their morphology and living habits:

In terms of living habits, the rhizomes of water ferns are short and upright, with a cluster of thick roots growing in the mud, while the thick-stemmed water ferns mostly float on the water surface;

In terms of plant shape, the petiole of water fern is narrow and not swollen, while the petiole and rachis of stubular water fern are broad and swollen, with a pointed base and the individual plant is obviously thicker than water fern.

In terms of leaf shape, both species have two types of leaves: fertile leaves and sterile leaves. The sterile leaves of water fern are deeply pinnately lobed 2-4 times, while the lobes of the sterile leaves of water fern are wide-banded.

Water fern specimen (dimorphic leaves) collected by Shanghai Natural History Museum

Image source: Shi Ruiping

Water fern specimen

Image source: https://www.cvh.ac.cn/

Cercidiphyllum serratum specimen

Image source: https://www.cvh.ac.cn/

Living plant of Cercidiphyllum scabra

Image source: weibo

Special reproduction of "fern fern"

Water ferns reproduce by spores. Sporangia grow along the meshes on both sides of the main vein of the fertile leaf lobes. When young, they are covered by continuous recurved leaf margins. When mature, they open to reveal the sporangium. The spores are tetrahedral, without a perimeter wall, and the outer wall is very thick, divided into inner and outer layers, with the outer layer having rib-like patterns.

Water fern sporophyte under the microscope

Image source: Wang Jinhu

The prothallus of a water fern is forming

Image source: Wang Jinhu

Similar to the water isoetes that we have introduced on our official account, water ferns and water isoetes were once widely distributed in the mud of ponds, paddy fields or ditches in my country's subtropical regions.

But now, with the reduction of wetland area, the canalization of farmland ditches and the changes in environmental water quality, it is difficult for us to find large-scale wild populations of water ferns or water isoetes in nature.

This is mainly because in the life history of water ferns, both the sporophyte and gametophyte generations have very strict requirements on water quality, and in a polluted environment, it is easy to cause abortion. Therefore, water ferns are also regarded as a sensitive wetland indicator species that can effectively monitor the health of soil and water environments.

The research results on water ferns in recent years also show that water ferns are good materials for studying the laws of plant genetic variation and growth and development mechanisms, and can even be used as a model plant for modern biological research. The scientific research value of water ferns has attracted the attention of the academic community. Because the number and population of wild water ferns are currently rare, the entire genus of water ferns is listed as a second-level protected plant in the latest version of the "National Key Protected Wild Plant List".

According to Peng Zhi, the first time he saw water ferns was in the waters of Taihu Lake near Moli Peak in Dongshan, Suzhou in 2008. The habitat of the reed marsh is very suitable for the growth and reproduction of water ferns. The wild population of water ferns in this habitat is large, and the individuals grow well. The plants can reach up to 1 meter in height.

Wild populations of water ferns found in the Taihu Lake Basin

Image source: Peng Zhi

The second time the water fern was observed was in Liantang Town, Qingpu District, Shanghai in 2009. This time it was found in a drainage ditch next to the Oriental fir and oak experimental site, but unfortunately there was only a single plant.

The population discovered this time is located in the Shanghai-Hangzhou High-Speed ​​Railway Ecological Corridor in Jinshan District. The number of individuals exceeds 200. It is the largest population ever discovered in Shanghai and it is also the first time that water ferns have been observed again after a lapse of 12 years.

Wild water ferns observed in Fengjing Town, Jinshan District

Image source: Peng Zhi

Protect the fern seeds and do not pick them randomly

So, now that we have discovered a rare wild population, how should we protect it?

The water fern discovered this time grew in the water accumulation of a drainage ditch under a beech forest, which was connected to the drainage ditch of the farmland, and there were scattered wild rice plants in the farmland. The living environment of the water fern overlaps with the agricultural production environment, and human interference is very frequent.

The most important thing to protect water ferns is to protect the ecological safety of their living environment, especially the cleanliness of drainage ditch water resources, avoid the use of fertilizers, pesticides, and herbicides, and avoid large-scale farmland operations. Secondly, the public should strengthen their awareness of protecting rare wild plant resources and avoid indiscriminate picking.

Habitat of the wild population of water fern discovered this time

Image source: Peng Zhi

The construction of Shanghai's ecological corridors began in 2016. The water fern population discovered this time appeared in the city's key ecological corridors, which fully demonstrated the achievements of Shanghai's urban ecological construction. In the future, I believe that with the joint efforts of the whole society, these endangered and extinct rare plants will surely return to the public's attention and reconstruct the colorful natural world of the city.

— References —

[1] Flora of China (Online Version). http://www.iplant.cn/frps2019/

[2] Li Jingyuan, Wang Taixia. Ceratophyllum is a good material for studying plant genetics[J]. Bulletin of Biology, 1997, 32(10):1

[3] Tao Ling, Yin Liyan, Li Wei. Effects of the herbicide benzylsulfuron-methyl on gametophyte growth and sexual organ differentiation of Ceratophyllum crassifolium[J]. Chinese Journal of Plant Ecology, 2008, 32(2):5.

Scientific review: Wang Jinhu, Associate Professor of Suzhou University of Science and Technology, Chairman of Suzhou Forestry Society

Edit: One week

The article is owned by Shanghai Natural History Museum