This plant has salt in it! But this salt is not the same as other salt!

Produced by: Science Popularization China

Author: Qin Yalong (Institute of Botany, Chinese Academy of Sciences, Jiangsu Province, Nanjing Zhongshan Botanical Garden)

Producer: China Science Expo

Editor's note: In order to decode the latest mysteries of life science, the China Science Popularization Frontier Science Project has launched a series of articles called "New Knowledge of Life" to interpret life phenomena and reveal biological mysteries from a unique perspective. Let us delve into the world of life and explore infinite possibilities.

In autumn, when walking through the mountains and forests, you will often come across Rhus chinensis Mill. in bloom. It is also called Rhus chinensis, Gallic acid, Gallic acid white, Red salt fruit, etc. It is a plant of the genus Rhus in the Anacardiaceae family, mostly in the form of shrubs. The wide panicles are densely distributed with small flowers, and bees and other insects come to visit the flowers from time to time.

Morphological characteristics of salt bran wood

Saltbran has pinnate compound leaves similar to those of Chinese toon and maple, but the only difference is that Chinese toon and maple have even pinnate compound leaves, while Saltbran has odd pinnate compound leaves. Its leaves are easy to identify, with multiple pairs of leaflets on both sides of the rachis, and the rachis has wing-like leaf-like wings, which is similar to maple, and is also the main feature for identifying them in the wild. Unlike ordinary plants, the leaflets of Saltbran gradually increase from bottom to top, and the leaflet at the top is generally the largest one.

Salt bran leaves

(Photo credit: Photo taken by the author)

Saltbran is a dioecious plant, with female and male flowers growing on different plants. If you see a saltbran bearing fruit, it must be a female plant. During the flowering season, the pistil of the male flower degenerates, the ovary is sterile, the stamen filaments are significantly elongated, and the anthers mature and release pollen. The stamens of the female flower degenerate, and the three stigmas of the pistil will turn from bright yellow to brown and finally black, and the ovary will gradually swell and develop into fruit.

Female inflorescence of Salicornia

(Photo credit: Photo taken by the author)

Male inflorescence of Salicornia

(Photo credit: Photo taken by the author)

During the flowering process, the flowers of the salt bran tree gradually bloom from the base of the inflorescence to the surrounding areas. Sometimes when the female flowers above are in full bloom, the female flowers at the base have already borne fruit, presenting a phenomenon of flowers blooming above and fruits bearing fruit below at the same time.

Studies have shown that, as an autumn nectar source plant, the nectar gland opening of the female flower of the salt bran tree is largest when the ovary is rose-red and the stigma is yellow, and the nectar gland opening is larger when the male flower petals are rolled down and not fallen than when the petals are not rolled down. Under the same conditions, the larger the nectar gland opening of the female and male flowers, the more nectar is secreted.

As time goes by, the salt bran tree gradually produces flat spherical drupes after flowering, called "salt bran", with a diameter of about 3-4 mm.

Infructescence of Salicornia

(Photo credit: Photo taken by the author)

This salt is not that salt

Li Shizhen described the morphological characteristics of the salt bran wood in detail in Compendium of Materia Medica: "The wood is shaped like a Chinese toon, with two opposite leaves, long and toothed, green on the front and white on the back, with fine hairs, and sour taste. Below the main leaf, there are straight leaves on both sides of the node, attached to the stem like arrow feathers. It blooms in May and June, and forms spikes of green and yellow, with many on one branch. It bears fruits in July, which are as big as small beans and flat, green when raw and slightly purple when ripe. Its kernel is light green and kidney-shaped, with a thin skin on the outside and a thin layer of salt on it. Children eat it. People in Yunnan and Sichuan collect it as wood salt. There are insects on the leaves, which form gallnuts, which are harvested in August."

From this record, we know that during the ripening process of the salt bran tree fruit, natural white salt crystals will grow on the surface of the fruit skin. If you observe carefully, you will find that salt crystals will precipitate on the leaves, fruits, petals and branches of the salt bran tree, but the crystals precipitated on the fruit are the most numerous and obvious, and are semi-melted. If you taste it lightly, it is salty with a little sourness. Some people with sensitive tastes can taste freshness. It has the effects of salt and MSG at the same time. People call it their own representative (bring) ("salt").

Salt crystals on the surface of the fruit of the salt bran tree

(Photo credit: Photo taken by the author)

The Compendium of Materia Medica also records: "Salt bran is also called salt skin, salt and rebel salt. In ancient times, the Shu people called it sour barrel or vinegar barrel, the Wu people called it salt bran, and the Rong people called it wood salt." Regarding the edible value of salt bran, it is recorded that "there is salt on it like snow, which can be used for soup. People in Lingnan take the seeds and grind them into powder to eat. The sour and salty taste quenches thirst and can prevent malaria." The Book of the Later Wei Dynasty records that the salt bran tree in the ancient Wuji Kingdom "has salty water vapor condensed, and salt grows on the tree, and there are also salt ponds."

Salt bran salt is different from table salt. It does not contain sodium chloride (NaCl), that is, it does not contain sodium ions (Na+) and chloride ions (Cl-) needed by our human body. Its main ingredient is calcium malate crystals, which is also the source of salty taste.

In the ancient times when salt was scarce, working people harvested the ripe fruits of the salt bran tree in their spare time from farming, and collected the precipitated salt frost as a substitute for table salt, so that they could taste the saltiness of food. However, this cannot replace table salt to maintain the normal functioning of our body's physiological functions. It was only done as a last resort in ancient times when there was a shortage of salt.

Edible value of salt bran

Salt bran wood has very strong adaptability and can grow in a variety of soil environments and climatic conditions. It is distributed in most provinces and regions of my country, growing in sparse forests or shrubs on sunny hillsides, valleys, and stream sides.

Salt bran wood has multiple edible values. When the branches and leaves sprout in spring, the young stems and leaves can be picked and used as wild vegetables. People have also developed its feeding value to pigs, which the locals call "pig-gnawing vegetables."

Saltbran is also a high-quality nectar plant. During the autumn flowering period, the huge number of small flowers on the inflorescence will attract bees to collect nectar, harvesting the rare autumn nectar - gallnut honey. The fresh fruit of Saltbran is also edible, but the taste and flavor are average, sour with a little salty.

In ancient times, the saltiness of salt bran could no longer satisfy people's taste buds. People picked the ripe fruits of the salt bran tree, boiled them in water, and filtered the resulting solution. The taste was similar to vinegar and could be used as a condiment. It also had a salty taste, so people could put less salt in cooking. The Classic of Mountains and Seas says: "There are many trees in Tuo Mountain. Guo Pu's note says: The tree comes from Sichuan. It grows in July and August. When it is ripe, if there is salt powder, it can be used to make vinegar soup."

Mature infructescence of Salicornia

(Photo credit: Photo taken by the author)

To this day, ethnic minorities such as the Dai and Hani in Yunnan still use mature salt bran as a seasoning when making ethnic specialties such as steamed buns, grilled fish, and jelly, which have a unique flavor.

Industrial value of salt bran wood

The salt bran tree is a gallnut tree. This is because gallnut aphids such as Schlechtendalia chinensis Bell and Schlechtendalia peitan will parasitize on the young leaf wings and leaflet petioles of the salt bran tree to form galls (yǐng), which is also called gallnut.

Galla chinensis

(Photo source: Chinese Herbal Medicine Knowledge University)

Gallnut is not the fruit of the salt bran tree, but the "house" formed by the proliferation of tissues of aphids parasitizing branches and leaves. In industry, gallnut can be used for tanning, medicine, plastics, petroleum, printing and dyeing, etc. At the same time, mature seeds can also be used to extract biomass diesel.

In addition, because salt bran wood is rich in tannin, it can react with ferrous acetate to form a non-water-soluble stable black substance, which is a good black dye. In ancient times, there were records of dyeing cloth, hair and teeth. Nowadays, there are also a small number of hair dyes with gallnuts added on the market. It should be reminded that due to the different physiques of each person and the complicated processing methods used in ancient times when dyeing hair, do not blindly try to pick and dye your hair by yourself, as it is likely to cause adverse reactions such as allergies.

The alternation of winter and summer between salt bran wood and lantern moss

In addition to its high edible, industrial and medicinal value, the salt bran tree also has high ornamental value. As the temperature drops in autumn and winter and the light hours become shorter, the color of its leaves will gradually change from green to yellow, orange-yellow, orange-red, and finally bright red. It stays on the branches and is not easy to wither, together depicting the picture of autumn. It is an autumn colorful leaf tree species with extremely high ornamental value.

Saltbran leaf discoloration

(Photo credit: Photo taken by the author)

You may be curious about why we often see saltweed but rarely see gallnuts growing on it. That is because gallnut aphids only parasitize on trees such as saltweed, green poplar, red poplar, and Pistacia chinensis Bunge in summer. In the cold winter, gallnut aphids need to migrate to Mnium to overwinter.

Therefore, in the process of planting salt bran wood to produce gallnuts, a certain area of ​​lantern moss needs to be planted to meet the overwintering needs of gallnut aphids.

The whole process starts when the gallnut matures. When the gallnut matures, it will burst naturally, and the aphids inside will migrate to the nearby lantern moss to reproduce and hibernate, until they emerge as spring aphids in March or April of the following year, and fly back to the salt bran wood to mate. The reproduced aphids climb onto the newly sprouted leaf wings and leaflet petioles to feed, thus forming galls, year after year.

Conclusion

Today, people no longer need to use the "salt" from the salt bran wood to replace table salt. Tasting it may be a cultural inheritance or just to evoke childhood memories. The autumn wind and red leaves are a good time to enjoy the autumn. Let's meet with nature and explore the colorful autumn colors of the salt bran wood in the mountains.

References:

1. Han Jiamin, Zhu Xin, Tan Hongwei, et al. Research on the nectar plant Rhus chinensis[J]. Chinese Bee Industry, 2022(005):073.

2. Jiang Guo. Development and Utilization of Rhus chinensis[J]. Agricultural Science and Technology: Mid-Monthly, 2020(11):135-136.

3. Sun Meirong, Zhang Zhaoyan, Research on the development and utilization of Rhus chinensis. Journal of Changwei Teachers College, 1997, 16(5).