KIRI TREE: CHARACTERISTICS, HABITAT, PROPERTIES, GROWTH - BIOLOGY - 2025

The kiri tree (Paulownia tomentosa) is native to China and has been cultivated in East Asia for more than 3,000 years. The species is considered to bring good luck and the Phoenix bird only perches on its branches.

This plant can reach 20 meters in height and has showy light purple flowers. The seeds are very small and winged. In a fruit there can be more than 2000 seeds that are dispersed by the wind.

Kiri tree (Paulownia tomentosa) Jean-Pol GRANDMONT, from Wikimedia Commons

The species is naturally distributed in western and central China, but is cultivated throughout the world mainly as an ornament. It naturally grows in open forests, as it demands a large amount of light for its development.

In the first year of life the growth of the plant is slow, but later it accelerates. The species can grow up to two meters each year to maturity and can live from 60 to 70 years.

The kiri tree has been used for thousands of years in traditional Chinese medicine. Almost all parts of the plant are used medicinally, mainly for its antimicrobial activity. Its potential use has also been proven in the treatment of some types of cancer, as well as various respiratory diseases.

characteristics

The kiri tree (Paulownia tomentosa) is also known as the empress tree, the princess tree or the imperial tree. This plant is cultivated in China mainly as an ornament and for its medicinal properties.

According to ancient Chinese legends, the Phoenix bird only perches on the branches of this tree. It was customary among the people of China to plant kiri trees around their houses to attract good luck and the Phoenix.

Phoenix. Bertuch-fabelwesen.JPG: Friedrich Johann Justin Bertuch (1747-1822) derivative work: Tsaag Valren, via Wikimedia Commons

Morphological description

Tree 8 to 12 m high, which in some cases reaches 20 m. It is deciduous (it loses its leaves at one time of the year) with a fairly extended crown. The trunk can measure 30 to 40 cm in diameter, being grayish in color. The bark is thin, rough and cracked in appearance.

The root system is quite widespread and deep, with supporting roots up to 8 m long. Absorption roots can be up to 60 cm long.

The leaves are simple, opposite and ovate. Its size ranges from 12 to 30 cm long by 15 to 30 cm wide. The margin of the leaf blade is entire, the apex acute and the base cordate (heart-shaped). The consistency is chartaceous (similar to cardboard) and pubescent (with hairs) both on the upper side and on the underside.

The inflorescences are cymose (indeterminate), terminal between 20 and 50 cm long. The flowers are hermaphroditic, pentameric (with five pieces per floral whorl). The calyx is fleshy, pubescent, bell-shaped. The corolla is tubular, bilabiate and light purple in color, with the tube 5 to 6 cm long.

Paulownia tomentosa flowers. The original uploader was Gmihail at Serbian Wikipedia., via Wikimedia Commons

The fruit is an ovoid loculicidal capsule with a woody consistency. The capsule is 2.5 to 5 cm long, dark brown in color at maturity, and remains on the plant through winter. The seeds are numerous, with several wings, 2.5 to 4 mm long.

Taxonomy

The species was described by Carl Thunberg in 1784 under the name of Bignonia tomentosa, being located in the Bignoniaceae family. Later, in 1841 Ernst von Steudel places it in the genus Paulownia.

The genus Paulownia was proposed in 1835 by Siebold and Zuccarini in a publication of the Flora of Japan. Paulownia was transferred to the Schrophulariaceae family and later separated to the Paulowniaceae family. This family was proposed by the Japanese Nakai in 1949, with a single gender (Paulownia).

The name Paulownia was dedicated to the Duchess Ana Pavlovna of Russia, who was the daughter of Tsar Paul I. The specific epithet tomentosa refers to the pubescence of the leaves of this species.

Two varieties are recognized for P. tomentosa. The tomentose variety is the most common and is characterized by abundant pubescence on the underside of the leaf. The variety tsinlingensis was described in 1976 by Gong Tong and is glabrous (without trichomes) or with few trichomes on the underside of the leaf.

Culture

No special land preparation is required for the cultivation of the species. It is convenient to moisten the soil before sowing to facilitate the work in the field.

Paulownia tomentosa is tolerant of different soil conditions, but is very sensitive to drainage problems. The best soils for cultivation are sandy or peat-rich soils that do not present water retention problems, and the ideal pH is between 5 and 8.

The species can grow in saline or nutrient-poor soils, due to its great capacity to selectively absorb Ca and Mg ions.

The recommended planting density is 400 to 500 plants per hectare. Sowing should be done in holes 70 to 80 cm long by 50 to 60 cm wide. Irrigation should be done twice the day of sowing and subsequently seven to eight days later.

To guarantee a good development of the main trunk, pruning should be carried out from the third or fourth year of cultivation.

Habitat and distribution

The species is native to western and central China. It is widely cultivated as an ornamental plant on all continents, with the exception of Antarctica.

In its natural habitat, P. tomentosa grows preferably in humid or semi-dry open forests below 1800 m in height.

The average annual temperature in its natural distribution area ranges from 11 to 17 ° C. However, they can tolerate extreme temperatures from -20 ° C to 40 ° C. Average annual rainfall in its area of ​​origin is in a range between 500 and 1500 mm, with 3 to 9 dry months.

The species is not tolerant of shade. It requires large amounts of light for rapid growth and prefers alkaline soils.

Increase

Seedling establishment may be poor under natural conditions. Survival increases in soils that have been tilled (68%) compared to untilled soils (40%). Additionally, a large amount of light is required to promote seedling growth.

Growth is slow during the first year, due to the further development of the root system. In a study carried out in the field in 2003, it was found that during the first three years of the plant's life the root system increases by 200%.

Image: Young tree of Pauwlonia tomentosa. Acabashi, from Wikimedia Commonsor CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)], from Wikimedia Commons

Later, growth is accelerated and plants can increase their height by 2 m and trunk diameter by 3 to 4 cm per year. Plant maturity (reproductive state) can be reached in the fourth or fifth year under favorable environmental conditions and in cultivated plants it can be at three years. In its natural range, the reproductive state can be reached by eight years of age.

Flowering occurs between April and May, and the fruits are formed between August and September. The capsules mature for several months and open in the spring when the seeds are dispersed. Trees are considered short-lived, as they only live between 60 and 70 years.

Seeds

The seeds of P. tomentosa are very small (2.5 to 4 mm wide) and weigh approximately 0.17 mg. They are oval in shape, with a reticulated surface and striated membranous wings.

Approximately 2,000 seeds are contained in a capsule and a tree can produce more than 20 million seeds per year. When the fruit ripens and opens, the seeds are dispersed by the wind at distances that can reach 3 km from the mother plant.

Paulownia tomentosa seeds. Steve Hurst, via Wikimedia Commons

The moisture content of the seeds is approximately 7% and they can survive in the soil seed bank for at least two to three years. The germination percentage reaches 90% in the first days after dispersal and subsequently decreases.

The seeds may present secondary dormancy (a state that prevents them from germinating) if they are subjected to unfavorable environmental conditions. Low temperatures, sudden changes in humidity and darkness can promote this dormancy.

Paulownia tomentosa capsules. Philmarin, from Wikimedia Commons

The light requirements of seeds for germination are much higher than in other species. In laboratory studies, the light ranges to stimulate germination range from minutes to hours depending on the age of the seed and storage conditions.

Health properties

The species has been used as a medicinal plant in traditional Chinese medicine. Already in 1578 Li Shizhen in "Compendium of Materia Medica" indicates that the bark of Paulownia is used to treat hemorrhoids and against parasites. It also indicates that the flowers are anti-inflammatory and help hair growth.

In traditional medicine the uses that are currently given are very wide. Both the bark of the plant and leaves, flowers and fruits are used. Other conditions include bronchitis, gonorrhea, mumps, asthma, diarrhea, conjunctivitis, hypertension, and tonsillitis.

Based on these uses, scientific research has been carried out to study the chemical compounds present in P. tomentosa. Also, some trials have been done to verify its effect in the treatment of various diseases.

The different parts of the plant, due to the different compounds they have, are used to treat various diseases.

Leaves

Flavonoids have been isolated in the leaves and have shown effects against free radical damage in cells. In addition, they produce a hydrocarbon of the terpene type (isoatriplicolide tiglate) with a potential carcinogenic effect and neuronal protection.

This terpene has been shown to cause apoptosis (programmed cell death) in cervical and lung cancer cells. On the other hand, extracts from the leaves have shown positive effects against glutamate toxicity in neuronal tissues.

flowers

The flowers have been widely used in traditional medicine. For the treatment of acne, a flower puree is prepared and applied directly to the condition.

Likewise, a flower decoction is prepared to treat mycosis (fungal infection) of the foot and in the treatment of empirosis.

Scientific research has shown the presence of numerous flavonoids in flowers. Among these, apigenin has been shown to have hypotensive, antioxidant, anti-inflammatory and vasorelaxant effects.

Apigenin has also shown anti-tumor effects in both in vitro and in vivo tests. This flavonoid inhibits the proliferation of cells that form tumors and stops the invasion of these cells.

On the other hand, the extracts obtained from the flowers of P. tomentosa inhibit the growth of some bacteria. The strongest effects have been proven against the proliferation of Staphylococcus aureus.

From dried flowers, a methanol extract is obtained that has potential antiviral activity against enterovirus 71 and coxsackie virus A16. These two viruses are the main pathogens that cause hand, foot, and mouth diseases.

Also, the essential oils present in the flowers of P. tomentosa showed an important antimicrobial activity in the presence of strains of Bacillus subtilis, Staphylococcus aureus and Escherichia coli.

Finally, it has been found that the flavonoids present in the flowers can reduce inflammation of the trachea and bronchi due to asthma.

Fruits and seeds

The fruits of this species have been found to be a natural source of antioxidants. In addition, they produce flavonoids that can improve Alzheimer's symptoms.

Likewise, the fruits contain compounds with antibacterial and antiviral activity. For example, it has been shown to be effective against Staphylococcus epidermidis.

Mimulone (flavonoid) isolated from P. tomentosa fruits has been shown to induce autophagy in lung cancer cells.

Acetone extracts have been obtained from the seeds and have been used effectively in the treatment of diabetes.

References

1. Essl F (2007) From ornamental to detrimental? The incipient invasion of Central Europe by Paulownia tomentosa Preslia 79: 377–389.
2. He T, BN Vaidya, ZD Perry and P Parajuli (2016) Paulownia as a medicinal tree: traditional uses and current advances. European Journal of Medicinal Plants 14: 1-15.
3. Innes, Robin J. 2009. Paulownia tomentosa. In: Fire Effects Information System,. US Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer).
4. Ji P, C Chen, Y Hu, Z Zhan, W Pan, R Li, E Li, H Ge and G Yang (2015) Antiviral Activity of Paulownia tomentosa against Enterovirus 71 of hand, foot, and mouth Disease. Pharm. Bull. 38, 1–6.
5. Johnson J, E Mitchem, D Kreh, E Richard. 2003. Establishing royal paulownia on the Virginia Piedmont. New Forests 25: 11-23.
6. His PT (1998) Paulownia. Flora of China 18: 8-10.
7. Zhu Z, C Chao, XY Lu and XY Gao (1996) Paulownia in China: cultivation and utilization. Asian Network for Biological Sciences, Beijing. 65 pp.