IngredientsEmpress tree (Paulownia tomentosa), also commonly known as princess tree or foxglove-tree, is a deciduous hardwood tree in the family Paulowniaceae, native to central and eastern China and the Korean Peninsula. The accepted scientific name is Paulownia tomentosa, with a number of synonyms reported in various literature, including Paulownia imperialis, Paulownia recurva, and Bignonia tomentosa.
In China, Paulownia is called "Pao Tong"; other names in common use are "Kiri" (Japan), "Odong-Namoo" (Korea), "Princess Tree," "Empress Tree," "Royal Princess Tree," and "Royal Paulownia." The generic name Paulownia honours Anna Pavlovna of Russia, who was Queen Consort of the Netherlands from 1840 to 1849, while the specific epithet tomentosa is a Latin word meaning "covered in hairs."
Paulownia tomentosa belongs to the family Paulowniaceae, sometimes referred to as Scrophulariaceae. The United States Department of Agriculture plant database identifies the species by the unique symbol "PATO2," with Paulownia tomentosa and Paulownia imperialis listed as synonym names.
The genus Paulownia mainly comprises nine fast-growing species: P. fortunei, P. tomentosa, P. elongata, P. albiphloea, P. australis, P. catalpifolia, P. kawakamii, P. fargesii, and P. taiwaniana. Of these, P. tomentosa, P. elongata, P. fortunei, and P. catalpifolia are considered the most popular. Growing interest in Paulownia has led to the development of various hybrids, the best-known being Clone in vitro 112, Shan Tong, Sundsu 11, and Cotevisa 2. Clone in vitro 112 is an artificially created hybrid of P. elongata and P. fortunei.
The tree grows 10–25 m (33–82 ft) tall, with large heart-shaped to five-lobed leaves 15–40 cm (6–16 in) across, arranged in opposite pairs on the stem. It is an extremely fast-growing tree with seeds that disperse readily and is considered an invasive exotic species in North America that has undergone naturalisation in large areas of the Eastern US. P. tomentosa has also been introduced to Western and Central Europe, establishing itself as a naturalised species there as well.
Though not regarded as a regular medicinal plant species, various plant parts (leaves, flowers, fruits, wood, bark, roots, and seeds) have been used for treating a variety of ailments. Each of these parts has been shown to contain one or more bioactive components, such as ursolic acid and matteucinol in the leaves; paulownin and d-sesamin in the wood/xylem; and syringin and catalpinoside in the bark.
The principal preparation forms documented in the scientific literature include:
Paulownia has been cultivated in southeastern Asia, especially China, for decorative, cultural, and medicinal purposes for over 2,000 years. Legends and records indicate that in ancient times people used Paulownia for various purposes. For many centuries, Chinese people planted Paulownia trees around their dwellings, believing it could bring good luck. According to records, even 2,600 years ago people were using Paulownia timber. The wood was used for the construction of houses, production of furniture and paper, handicrafts, farm implements, musical instruments, and also for medicinal properties.
Paulownia tomentosa and Paulownia fortunei are described in the Chinese "Compendium of Materia Medica," the reference appearing under Drug 35-11, page 3034, in the 2003 English translation.
Paulownia tomentosa Steud., a traditional Chinese medicinal plant, was used for many centuries in Chinese herbal medicine as a component of remedies for many illnesses, including inflammatory diseases. In traditional Chinese medicine, extracts from the wood, fruit, and bark were used to treat bronchitis, asthma, and bacterial infections.
In traditional Chinese medicine, P. tomentosa parts such as flowers and bark are used to tonify the lungs and treat conditions like bronchitis and tonsillitis, often as an expectorant and anti-inflammatory agent.
Paulownia flowers have been used in folk medicine for thousands of years; in traditional Chinese medicine, they have been used for treating infections, inflammation, and injury.
The flower, leaf, skin, root, and fruit of Paulownia fortunei are of medical value and reported for use in treating infections, inflammation, and injury, and in anti-tumor preparations. The bark is reported for use in treating orthopaedic disease, hemorrhoids, and foot odor, and the epicarp of the fruit for antimicrobial activity. The leaves are reported for use in dissolving pyogenic infections and promoting hair growth.
A decoction of the leaves is used to wash foul ulcers and is also said to promote the growth of hair and prevent greying. The leaves are also poulticed onto bruises. The leaf juice is used in the treatment of warts. The flowers are used in the treatment of skin ailments.
A tincture of the inner bark is used in the treatment of fevers and delirium; it is considered astringent and vermifuge.
Folk remedies in China use mashed empress tree flowers to treat acne vulgaris and the decoction to treat fungal infections on the sole of the foot and the skin between toes. Flowers are also used in the treatment of first- to second-degree burns.
In Japan, the tradition of planting an empress tree to celebrate a daughter's birth weaves family heritage with forestry; as the tree matures, it is transformed into a wedding chest, symbolizing growth and continuity. The wood of such trees is popular for making soundboards of stringed instruments in Japan, China, and Korea, and is also popular with timber merchants for making furniture.
Flavonoids, lignans, phenolic glycosides, quinones, terpenoids, glycerides, phenolic acids, and miscellaneous other compounds have been isolated from different parts of the P. tomentosa plant. It is a member of the plant family Paulowniaceae and a rich source of biologically active secondary metabolites, traditionally used in Chinese herbal medicine.
The fruit of P. tomentosa is particularly rich in a structurally distinctive class of compounds: the C-geranylated flavonoids. It is a rich source of phenolic compounds, mainly geranylated flavonoids, which are currently studied for their promising biological activities.
Paulownia tomentosa harbours a large pool of metabolites of which geranylated flavonoids are the major bioactive members. Various studies have revealed the antioxidant effects of these compounds. Spectroscopic analyses have shown that these flavonoids are characterized by the presence of a geranyl group at their C-6 position. Eight such compounds isolated from methanolic extracts include flavanones like mimulone, 3′-O-methyldiplacone, 4′-O-methyldiplacone, and dihydroflavonols like 3′-O-methyldiplacol and 4′-O-methyldiplacol.
Eleven new C-geranylated flavonoids — tomentodiplacones L, M, and N; tomentodiplacol B; 3′,4′-O-dimethyl-5′-hydroxydiplacone; mimulones F, G, and H; paulowniones A and B; tomentone; and 3′,4′,5′-trimethoxyflavanone — together with 11 known flavonoids, were isolated from fruits of Paulownia tomentosa. Among the major geranylated compounds characterized from P. tomentosa fruit are tomentone, diplacone, mimulone, 5,7-dihydroxy-6-geranylchromone, tomentodiplacone M, tomentodiplacone L, tomentodiplacone N, 3′-O-methyldiplacol, and 3′-O-methyl-5′-methoxydiplacol.
The bark of P. tomentosa contains eight phenolic compounds: glucodistylin, luteolin, ellagic acid, cistanoside F, campneoside II, isocampneoside II, and verbascoside, among others. Nine phenolic extractives including two flavonoids (naringenin and quercetin), two phenolic acids (cinnamic acid and gallic acid), and five phenylpropanoid glycosides (cistanoside F, acteoside, isoacteoside, campneoside II, and isocampneoside II) have also been reported.
Verbascoside, oxoverbascoside, methoxyverbascoside, and hydroxyverbascoside have been detected in Paulownia flowers, with oxoverbascoside content reaching 1.23 ± 0.05 mg/g dry mass.
Paulownin, also known as isopaulownin or neopaulownin, is a lignan isolated from aerial parts of various plants — and from the wood of P. tomentosa in particular. It has been the subject of investigation for NF-κB inhibitory and skin-protective activity (see Section 5.4).
The trees of the Paulownia genus produce many promising chemical compounds, including verbascoside, diplacone, mimulone, apigenin, catalpol, aucubin, and maslinic acid, with various biological activities including antioxidant, anti-inflammatory, and antiproliferative effects.
The fruits contain fatty oils, alkaloids, flavanones, and flavonoids with antioxidant properties. The flavonoid content in Paulownia flowers is high, and these flavonoids have good antioxidant and antibacterial activities in vitro.
A variety of biologically active components, including polyphenols and polysaccharides, have been discovered in Paulownia tomentosa. Paulownia tomentosa flower polysaccharide (PTFP) is among the principal active components. Polysaccharides are a common type of biological macromolecule in traditional herbal medicine with various biological properties, including antiviral, antitumor, antioxidant, anti-inflammatory, hypoglycemic, and immunomodulatory properties.
In biological activity assays with human alveolar basal epithelial cells, the expression of TNF-α-induced proinflammatory cytokines (IL-8 and IL-6) was reduced significantly by the EtOAc fraction of a P. tomentosa extract as well as by the new compounds isolated from this fraction.
The ability of C-geranylated flavonoids to reduce the production of the pro-inflammatory cytokine TNF-α in THP-1 cells after bacterial lipopolysaccharide stimulation was evaluated using an in vitro screening test, and preliminary structure–activity relationships of these derivatives were also studied, including the correlation of TNF-α inhibitory activity with lipophilicity.
Several compounds from P. tomentosa were selected for determination of their effect on 5-LOX; compounds diplacone (IC50 0.05 µM) and a related flavonoid (IC50 0.06 µM) showed activities almost 10 times greater than that of zileuton (IC50 0.35 µM) as the positive control.
Stem bark extracts suppressed nitric oxide production in LPS-stimulated RAW 264.7 macrophages, suggesting inhibition of pro-inflammatory pathways such as iNOS expression; key compounds like verbascoside contribute to this activity by modulating cytokine release in cellular assays.
The majority of C-geranylated isolates from P. tomentosa fruits were found to inhibit human neutrophil elastase (HNE) activity, with IC50 values ranging from 2.4 ± 1.0 to 74.7 ± 8.5 μM.
Paulownia flowers display antioxidant activity, thereby effectively reducing the damage of free radical oxidation to the organism. Phenylpropanoid glycosides, including paulowninosides B, D, and F, showed remarkable antioxidant activity by effectively protecting NRK52e cells from H2O2-induced oxidative injury; the cell protection indices were even higher than those of vitamin E (a standard antioxidant comparator) in the presence of these paulowninosides.
Flavonoids are known to exhibit strong antioxidant activity through free radical scavenging, as well as anti-inflammatory, antimicrobial, and anti-cancer properties. Additionally, flavonoids can ameliorate health issues caused by a high-fat diet, including hyperlipidemia, fatty liver disease, and insulin resistance, through the AMP-activated protein kinase pathway.
Protein tyrosine phosphatase 1B (PTP1B) and α-glucosidase are important targets for the treatment of obesity and diabetes, due to their deep correlation with insulin and leptin signalling and glucose regulation. The methanol extract of Paulownia tomentosa fruits showed potent inhibition against both enzymes. Purification of this extract led to eight geranylated flavonoids displaying dual inhibition of PTP1B and α-glucosidase. The isolated compounds were identified as flavanones and dihydroflavonols. Most compounds were highly effective against PTP1B (IC50 = 1.9–8.2 μM); mimulone was the most effective against PTP1B with IC50 = 1.9 μM, whereas a C-6 geranylated pentahydroxy flavane displayed potent inhibition against α-glucosidase (IC50 = 2.2 μM).
Purification of the methanol extract of Paulownia tomentosa fruits yielded potent human acetylcholinesterase (hAChE) and butyrylcholinesterase (BChE) inhibitory flavonoids. A comparative activity screen indicated that a geranyl group at C-6 is crucial for both hAChE and BChE activity. For example, diplacone showed 250-fold higher efficacy than its parent compound eriodictyol. IC50 values of diplacone were 7.2 ÎĽM for hAChE and 1.4 ÎĽM for BChE.
Similar trends were also observed for 4′-O-methyldiplacone (versus hesperetin) and mimulone (versus naringenin). Representative inhibitors showed mixed inhibition kinetics as well as time-dependent, reversible inhibition toward hAChE.
Paulownin and paulownin-rich extracts from wood of Paulownia tomentosa were studied for their anti-inflammatory activity and skin-protective effects. Preincubation with Princess Tree wood extract at concentrations from 0.1% to 5% significantly inhibited pro-inflammatory cytokine release. NF-ÎşB inhibition by extracts of Paulownia tomentosa wood has been proposed as a key mechanism; compositions comprising NF-ÎşB inhibitors include extracts of Paulownia tomentosa wood.
A study aimed at investigating the antiviral effect of Paulownia tomentosa Steud extract against SARS-CoV-2 found that the extract can inhibit viral replication by directly interacting with both the 3-chymotrypsin-like protease and spike protein. The extract did not reduce lung epithelial cell viability and exerted a protective action in cells damaged by tert-butyl hydroperoxide. These data suggest the potential role of the extract in COVID-19 treatment as both an antiviral and a cytoprotective agent in vitro.
Twelve geranylated flavonoids from Paulownia tomentosa displayed dose-dependent SARS-CoV PLpro mixed inhibition using a fluorogenic assay.
Evidence type: Predominantly in vitro (cell-based) and animal studies; no published human clinical trials identified.
A study aimed to isolate minor geranylated flavanones and flavones from P. tomentosa fruit and evaluate their cytotoxicity and possible anti-inflammatory effects in a cell-based model of inflammation. Chromatographic separation of a chloroform portion of the ethanolic extract of P. tomentosa fruit led to the isolation of twenty-seven flavonoids (1–27), twenty-six of them geranylated with different modifications. Results confirmed that constituents from this traditional Chinese medicinal plant have promising anti-inflammatory activities and can serve as a potential source of inspiration for new anti-inflammatory medications.
Diplacone and mimulone, two geranylated flavanones from P. tomentosa, were tested in vivo in a model of colitis in rats; they ameliorated the symptoms of colitis, delayed their onset, and reduced the levels of antioxidant enzymes. This constitutes animal-level evidence only.
Clinical trials validating these anti-inflammatory uses are limited, with most evidence derived from preclinical studies.
Evidence type: In vitro and cell-based; no human clinical trials identified.
Diplacone and related compounds protected premature senescent human embryonic lung diploid fibroblast cells at 10 µM from ageing induced by H2O2. Thirteen C-geranylated flavonoids isolated from P. catalpifolia were evaluated for their antioxidant activity on HUVEC injury induced by homocysteine or H2O2; several compounds showed improved proliferative activity at 10 µM, however, at 20 µM or higher, diplacone expressed cytotoxic activity to HUVECs and reduced its proliferative activity.
Strength of evidence: Preliminary; all work is cell-based or in vitro. No clinical or human data are currently available.
Evidence type: In vitro only.
Antimicrobial properties of P. tomentosa extracts target various bacteria and fungi, with fruit and stem extracts showing activity against Staphylococcus aureus (MIC 32–64 μg/mL) and Streptococcus pyogenes. These effects, driven by geranylated flavonoids, extend to potential wound healing applications.
Total ethanolic extract and chloroform fraction showed MICs of 128 and 32 μg/mL, respectively, against S. aureus. Diplacol, diplacone, and 3′-O-methyl-5′-hydroxydiplacone inhibited S. aureus growth in the range of 8–16 μg/mL. Synergistic potential was shown in combination with mupirocin and fusidic acid. The ethanolic extract and the chloroform fraction destroyed the cell membranes of S. aureus by 91.61% and 79.46%, respectively, while the pure compounds were less active. The ethanolic extract and the pure compounds reduced the number of adhered cells to 47.33–10.26% compared to untreated control.
Recent studies found that aqueous extracts of P. elongata leaves show significant antimicrobial activity against pathogens like Salmonella and Staphylococcus aureus.
Strength of evidence: In vitro data only. No clinical antimicrobial trials have been published for this plant.
Evidence type: In vitro, ex vivo epidermal equivalent models, and patent disclosures. No published RCTs or clinical trials identified in peer-reviewed literature.
Paulownin and paulownin-rich extracts from wood of Paulownia tomentosa were studied for their anti-inflammatory activity and skin-protective effects. Preincubation with Princess Tree wood extract at concentrations from 0.1% to 5% significantly inhibited pro-inflammatory cytokine release. In the cited study, epidermal equivalents were topically treated (2 mg/cm²) with Princess Tree extracts in a 70% ethanol/30% propylene glycol vehicle two hours before exposure to solar ultraviolet light (UV dose applied: 70 kJ/m² as measured at 360 nm). Supernatants were analyzed after 24 hours for IL-1α and IL-8 cytokine release.
Extracts of Paulownia tomentosa wood have been found to exhibit significant properties for skin including skin lightening, improving signs of aging, and reducing inflammation. These findings are largely from patent disclosures by industrial applicants and have not yet been validated in published peer-reviewed human clinical trials.
Evidence type: In vitro only (cell culture and enzyme assays).
Anti-viral properties have been identified from stem bark extracts of P. tomentosa. In the context of SARS-type coronaviruses, twelve geranylated flavonoids from Paulownia tomentosa displayed dose-dependent SARS-CoV papain-like protease (PLpro) mixed inhibition using a fluorogenic assay. In a study against SARS-CoV-2, the extract was found to inhibit viral replication by directly interacting with both the 3-chymotrypsin-like protease and spike protein; the extract did not reduce lung epithelial cell viability and exerted a protective action in cells damaged by oxidative stress. These data suggest the potential role of the extract in COVID-19 treatment as both an antiviral and a cytoprotective agent in vitro.
Strength of evidence: Preliminary in vitro data only. No human antiviral trials have been conducted.
Evidence type: In vitro (cell line) studies only.
Among the recorded biological activities: P. tomentosa fruits have shown anticancer activity against human lung adenocarcinoma cells, and P. coreana leaves have shown anticancer activity against breast and cervical cancer cell lines in vitro.
Phytoconstituents previously isolated from P. tomentosa were evaluated; acteoside was determined to be the most cytotoxic on plant BY-2 cells, while diplacone showed the highest cytotoxicity on the K562 human erythro-leukaemia cell line.
Results of one study suggest that paulownin enhances NK cell cytotoxicity by activating the JNK signalling pathway, providing implications for developing new strategies for cancer immunotherapy.
Strength of evidence: All findings are from cell line studies. There are no animal model studies demonstrating in vivo tumour reduction attributable to P. tomentosa preparations, and no clinical oncology data exist.
Evidence type: In vitro enzyme inhibition; no human clinical trials identified.
The methanol extract of P. tomentosa fruits was characterized as a source of PTP1B and α-glucosidase inhibitors; eight isolated C-geranylated flavonoids displayed dual inhibition of PTP1B and α-glucosidase. α-Glucosidase catalyzes the hydrolysis of α-1,4-glycosidic bonds to release α-glucose; effective α-glucosidase inhibitors can delay carbohydrate digestion and reduce postprandial hyperglycaemia.
Strength of evidence: Preliminary. All work is in vitro enzyme inhibition only; no glucose-lowering clinical data exist.
Evidence type: In vitro (cell-based) only.
The neuroprotective effects of mimulone and diplacone against glutamate-induced neurotoxicity were studied in primary cultured rat cortical cells. It was found that only diplacone weakly attenuated glutamate-induced toxicity at 10 µM.
Inhibition of human acetylcholinesterase (hAChE) and butyrylcholinesterase (BChE) has been linked to amelioration of Alzheimer's symptoms; research into natural inhibitors is considered of critical importance. As noted in Section 4.4, diplacone and related geranylated flavanones from P. tomentosa showed potent in vitro cholinesterase inhibition. No human cognitive outcomes have been assessed.
Evidence type: In vitro only.
The antiparasitic activities of Paulownia C-geranylated flavonoids involve effects on Leishmania species; 3′-O-methyldiplacone and 3′-O-methyl-5′-O-methyldiplacone achieved significant antileishmanial activity with IC50 values of 10.4 and 12.7 μM against L. donovani, and 11.3 and 8.0 μM against L. braziliensis, respectively — comparable to miltefosine as positive control at 9.5 and 6.7 μM. Diplacone was also active (IC50 1.4 µg/mL) against the related kinetoplastid parasite Trypanosoma brucei brucei.
Studies have confirmed P. tomentosa's anti-inflammatory, antioxidant, antibacterial, antiviral, and neuroprotective properties in preclinical models. The following body systems are associated with research on this plant:
No human clinical dosage recommendations exist in peer-reviewed literature for empress tree preparations. The following dosages are those used or discussed in preclinical experimental contexts only:
No standardized extract, approved supplement dosage, or pharmacopeial monograph specifying human doses of empress tree preparations has been identified in the searched literature. There is no established EMA or ESCOP monograph for this species.
Many compounds from Paulownia demonstrate various biological activities and are promising candidates for natural preparations; however, further in vivo studies are needed to clarify the exact mechanism of action of the active substances and their long-term effects.
At 20 µM or higher concentrations, diplacone expressed cytotoxic activity to human umbilical vein endothelial cells (HUVECs) and reduced their proliferative activity. This dose-dependent cytotoxicity at higher concentrations was demonstrated only in cell culture. Acteoside was determined to be the most cytotoxic of the compounds tested on plant BY-2 cells, and diplacone on the K562 human erythro-leukaemia cell line.
The plant has been noted in ethnobotanical sources as containing some potentially toxic compounds. The identity and human-relevant toxicity thresholds of these compounds have not been specifically characterised in the available peer-reviewed clinical literature.
The inhibition of NF-ÎşB signaling by paulownin and wood extracts is proposed as a beneficial mechanism for skin and inflammatory applications. However, because NF-ÎşB is a central regulator of immune function, significant or systemic NF-ÎşB suppression carries theoretical implications for immune surveillance that have not been evaluated in human studies.
No published human pharmacokinetic studies for any standardised P. tomentosa preparation or isolated compound (including diplacone, mimulone, verbascoside, or paulownin) were identified in this review. Clinical trials validating the uses documented for this plant are limited, with most evidence derived from preclinical studies.
Based on identified mechanisms — including cholinesterase inhibition, COX and 5-LOX inhibition, PTP1B inhibition, and NF-κB modulation — theoretical interactions with cholinesterase inhibitor drugs (e.g., donepezil), NSAIDs, antidiabetic agents, and immunosuppressants are conceivable. No human interaction studies have been reported in the peer-reviewed literature.
P. tomentosa is considered an invasive exotic species in North America that has undergone naturalisation in large areas of the Eastern US. This status has ecological implications for sourcing, and material identity verification is important given the existence of multiple closely related species with overlapping common names.
Health conditions that Empresstree may help support.
Body systems that Empresstree may help support.
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