How many of these “cute” mangrove plant names have you heard of?

Produced by: Science Popularization China

Author: Cao Cheng'e (Wuhan Botanical Garden, Chinese Academy of Sciences)

Producer: China Science Expo

Mangroves are known as one of the most productive natural marine ecosystems on Earth. They play an important role in maintaining coastal biodiversity, purifying water quality, preventing wind and waves, promoting siltation and protecting banks, regulating water and gas balance, and beautifying coastal landscapes.

Photo: Mangroves

(Photo source: Veer Gallery)

These trees have brown trunks and green branches and leaves, and look similar to ordinary trees, so why are they called mangroves?

This is because the trunks of mangrove plants are rich in magical tannins. Once the bark is scraped off and exposed to the air, it will quickly oxidize into red, so they are called "mangroves".

Picture: The bark of a mangrove plant turns red after being scraped

(Image source: China Plant Image Library)

Mangrove plants can be divided into true mangroves and semi-mangroves according to their habitat. True mangroves usually refer to plants that can only grow and reproduce in intertidal environments. Common characteristics include viviparity, respiratory roots and prop roots, salt-secreting tissues and high osmotic pressure. Semi-mangroves are amphibious plants that can survive in intertidal zones (and become dominant species on beaches) and reproduce naturally in terrestrial environments.

Today, let’s take a look at these magical and interesting mangrove plants.

The nectar plant in the seawater - Candle fruit

Aegiceras corniculatum (L.) Blanco is a shrub or small tree of the Primulaceae family. It is also called the Paulownia tree. The leathery leaves are alternate, and the branches are almost opposite at the top. White bell-shaped flowers gather at the top of the branches to form an umbel. The fruit is a cylindrical capsule with a slightly curved shape, which looks like a small pepper, a crescent moon, or a candle.

Picture: Candlenut fruit

(Image source: China Plant Image Library)

Candle fruit is an excellent nectar plant. After the flowers open, they have fragrance, secrete a lot of nectar and have more pollen, which can attract a large number of bees to collect nectar. The nectar in the flowers is white and transparent, with a low concentration and a fragrant smell; the pollen is rich in nutrients such as vitamins, phospholipids, organic acids and sugars.

Photo: Flowers of the candle fruit

(Image source: China Plant Image Library)

In order to allow the offspring to reproduce better, the fruits of the candle fruit will fall off the mother tree and onto the mudflats after they mature. After absorbing water, the peel will burst, and the rudimentary seedlings inside will extend out of the peel and quickly take root and grow.

Facing the salty seawater, the candle fruit has developed a salt excretion mechanism. It secretes the salt absorbed into the plant body through the leaf glands (salt glands) on the leaves, forming salt crystals on the leaf surface. The salt crystals can be washed away by tides, rain or fall with the leaves, reducing the salt content of the tree.

The candle fruit tree has a beautiful shape and red twigs, which can form a spectacular mangrove landscape. It is suitable for planting in coastal ecological landscape forest belts. It has both wind and wave protection functions and high ornamental value. At the same time, its bark contains tannins, which can be used as raw material for extracting tannin, and its wood is a good firewood.

Acanthus paniculatus - a plant with fruit that looks like a little mouse

Acanthus ilicifolius L.Sp. is an upright evergreen shrub of the Acanthaceae family, up to 2 meters high. It has a well-developed root system with spongy aerenchyma, an upright stem, and drooping branches that gradually form prop roots, thus spreading and expanding to form new plants; the leaves are hard and smooth, oblong, with sharp tips and thorn-like teeth on the edges. Like the candle fruit, the leaves can also secrete the salt absorbed into the plant body through the leaf glands; the white or light blue-purple flowers are densely gathered into spikes and grow at the top of the branches; the oblong fruits contain light yellow flat seeds.

Photo: Flowers of Acanthus

(Image source: China Plant Image Library)

When you hear the name "Acanthus fragrans", are you curious? What does such a beautiful plant have to do with mice?

It turns out that the oval fruit of the mouse vine has a long style behind it, just like the body and tail of a mouse. "Lā" means thorn, and its leaf edges have sharp serrations, which is the origin of the name of the mouse vine. Isn't it very vivid?

Picture: Acanthus fruit

(Image source: China Plant Image Library)

Acanthus fragrans often grows in the lower layer of mangroves. It has supporting roots and breathing roots, and has the functions of preventing wind and waves, promoting siltation and protecting beaches, and consolidating banks and embankments.

Bruguiera gymnorrhiza, a plant with a cable-like root

Bruguiera gymnorhiza (Linnaeus) Savigny is a tree or shrub of the genus Bruguiera in the family Rhizophoraceae. Its bark is gray-black with rough cracks; its leaves are elliptical and oblong, with short tips and cuneate bases; its petioles are dark green and its stipules are light red; it often grows in slightly arid, well-ventilated salt flats that extend inland, forming a natural and stable ecological plant landscape.

It is reported that in Malaysia, most of them are pure forests, with trees more than 20 meters tall and 65 centimeters in diameter. However, in our country, the height of the Bruguiera gymnorrhiza found so far rarely exceeds 6 meters, and there are no pure forests, and most of them are scattered.

The leathery and fleshy calyx of Bruguiera is very eye-catching. When its flowers are in bud, the calyx is tightly huddled together, like small pink olives; when the flowers bloom, the calyx faces downward, with more than a dozen lobes like small claws, and the appearance of the flower cannot be seen clearly; lift it up and turn it over, and you can see the long petals, dark red with a little red, slightly shorter than the calyx.

Figure: Flowers of Bruguiera gymnorrhiza

(Image source: China Plant Image Library)

Picture: Fruit of Bruguiera gymnorrhiza

(Image source: China Plant Image Library)

Bruguiera gymnorrhiza has obvious characteristics of viviparity and prop roots. The long hypocotyl is conical, and the persistent calyx is like a pink cap worn on the top of the hypocotyl. The small claws of the lobes seem to be holding the hypocotyl tightly. When the hypocotyl matures, it falls into the mud and quickly takes root and grows into a seedling. The hypocotyl of Bruguiera gymnorrhiza is rich in starch. After the tannin is processed, rice flour and sweet potato flour are added to make rice cakes, which were once life-saving food during famines.

Figure: Viviparity of Bruguiera gymnorrhiza

(Image source: China Plant Image Library)

The prop roots of Bruguiera gymnorrhiza are quite developed and have many branches. When growing, the base of the root grows rapidly first, pushing up the tip of the root and exposing it to the ground. Then, the growth rate of the top of the root accelerates and exceeds the growth rate of the base, while the growth rate of the base slows down. In this way, the raised part of the root bends downward again, forming a shape like a human knee. Each root repeats the above growth process, growing many large and small "knees", forming a peculiar "knee-shaped" root landscape. It is precisely because of the intertwined knee-shaped roots produced by Bruguiera gymnorrhiza, which are like cables, that it is named Bruguiera gymnorrhiza.

Figure: Knee-shaped roots of Bruguiera gymnorrhiza

(Image source: China Plant Image Library)

The only fern in the mangroves - Halophyte

Acrostichum aureum L. is a herbaceous plant of the genus Acrostichum in the family Pteridaceae. It is one of the tree species that make up the mangrove forest and the only fern plant. Acrostichum aureum is found in Guangdong, Hainan, and Yunnan in China, growing on mudflats along the coast or riverbanks; it is also found in other tropical regions in Asia, Africa, and tropical America.

Image: Halophyte plant

(Image source: China Plant Image Library)

The plant of the fern can be up to 2 meters tall. The leaves grow in clusters and are divided into two parts: the upper reproductive leaves are responsible for producing spores for reproduction, and the lower nutritional leaves are responsible for photosynthesis and providing nutrition. The yellow-brown leaves are what the reproductive leaves look like when they are mature, and they look like they are dried.

Image: Halophyte leaves

(Image source: China Plant Image Library)

The most special thing about the fern is that it has the dual characteristics of lower plants and mangrove plants. The secondary metabolites have relatively unique biological activities and have certain medicinal value.

Conclusion

Rich and diverse mangrove plants grow on the shallows of the land-sea interface. They, together with fungi, algae, invertebrates, birds and mammals, form a special mangrove ecosystem. Its roots and trunks can provide a medium for crabs and gastropods to cling to and a place to forage; fallen leaves can be eaten by some animals, or provide food for benthic animals after decomposition; the rich animal resources and luxuriant branches are a place for water birds to forage, live and breed, and are also a wintering ground and migration transit station for migratory birds.

Mangrove plant communities are both forests and wetlands, and they have the functions of both "lungs" and "kidneys" of the earth. They play an important role in maintaining biodiversity conservation and are truly "green lungs of the ocean, heroes of shore protection, bird paradise, and fish and shrimp granary." If you can, please remember their names.

References:

1. Tiffany Duong. Why planting mangroves can help save the planet

2. Flora of China Electronic Edition

3. Shenzhen Municipal Planning and Natural Resources Bureau. What are the definitions of true mangroves and semi-mangroves?

4. He Ruirong. Research on mangroves and their protection in Macao[D]. Master's thesis of Jinan University, 2019.

5. Fan Hangqing, Mo Zhucheng. History, achievements and lessons learned from the restoration of mangroves in Guangxi [J]. Guangxi Science, 2018, 25(4): 363-371, 387. 6. Xu Wanlin. Nectar plants on the sea mudflats: Candle fruit [J]. Beekeeping Technology, 1992(1): 33-35.

7. Zhao Huaibao, Yin Shouyan. Tissue culture of mangrove plant Pteris serrata[J]. Journal of Hainan Tropical Ocean University. 2019, 26(05): 34-39.

8. Zeng Xianguang. Current status and protection strategies of mangrove wetland resources in Huizhou[J]. Journal of Huizhou University (Natural Science Edition), 2008(6):55-57.

(Note: Latin text should be italicized.)