The genus Tradescantia, commonly known as ‘Spiderwort’, is the second largest genus within the Commelinaceae family [1] including approximately 80 herbaceous species classified into 12 sections [2, 3, 4, 5, 6, 7, 8, 9, 10]. These species are indigenous to the Neotropics, and the centre of diversity is located in the southern United States and Mexico [3, 5, 8, 9, 11] (Table 1, Ref. [2, 3, 4, 9, 10, 11, 12, 13, 14, 15]). These species are adapted to full sun, deep shade, high or low temperatures, and xeric habitats [16].

Tradescantia species are evergreen, perennial or annual, rupicolous or epiphytic, and can reach up to 30–60 cm in height. Roots are thin or thick, and fibrous or tuberous. Stems are aerial, rarely subterranean, prostrate with an ascending or erect apex, forming intertwined dense mats. Leaves are simple, 3–45 cm long, sessile to sub-sessile, distichously or spirally alternate, glabrous, lanceolate to linear-lanceolate to ovate, evenly distributed along the stem or crowded at the apex. The inflorescence is a terminal crescent, pedunculated, sub-umbelled, with cincinni bracts as leaves or reduced (bracteous), spataceous. Flowers are bisexual, actinomorphic or slightly zygomorphic, pedicellate, pedicel glabrous and green. Sepals are green, equal or subequal, polysepalous or connate below and persistent. Petals can be white, pink, or purple, but mostly bright blue, equal or subequal, and free or connate below the floral tube. Stamens are equal or subequal, epipetalous; filaments free, usually bearded at the base, glabrous or with moniliform hyaline trichomes at the base, anthers oblong or reniform, basifixed or dorsifixed. Carpels are pubescent, ovary 3-locular, style straight, cylindrical to sub-cylindrical, glabrous. The fruit is a 3-cell loculicidal capsule. Seeds 1–2 per locule, reniform to ellipsoid usually rugose [2, 12, 13].

T. zebrina Bosse, T. fluminensis Vell., T. spathacea Swartz. and T. albiflora Kunth. are the most widely studied species within the Tradescantia genus. Ethnopharmacological uses of Tradescantia include anti-inflammatory, antioxidant, antibacterial and antiarrhythmic applications. All parts of the plant are potentially useful and, although the phytochemical characterization has been described for some species, most Tradescantia species remain unreported. No species have been tested for drug development aside from toxicity studies. Thus, the objective of this review is to describe all known aspects of the genus Tradescantia including its botanical characteristics, traditional uses, phytochemical composition, biological activities, and safety aspects.

A literature search was performed in PubMed/MEDLINE using the terms ‘Tradescantia’ and ‘global distribution’, ‘traditional uses’, ‘phytochemical’, ‘antioxidant’, ‘inflammatory’, ‘biological properties’ or ‘human health’, individually or in combination. Scientific articles from the last five years including the phytochemical characterization and evaluation of biological properties of Tradescantia species through in vitro and in vivo models, were prioritized for inclusion in this review.

Herbs have traditionally beed used for their fragrance, taste, and therapeutic properties. Fresh or dried herbs have been applied in tablet or capsule form as contemporary methods (powders, teas and extracts) [17]. Some species of the genus Tradescantia have been traditionally used for their presumed anti-inflammatory, antioxidant, antibacterial and antiarrhythmic properties. For example, roots have been used as a drink to heal kidney diseases and digestive system ailments. Leaves have been applied to relieve stings and insect bites. A summary of worldwide traditional uses of the genus Tradescantia is shown in Table 2 (Ref. [18, 19, 20, 21, 22, 23, 24, 25, 26, 27]). Traditional remedies must be interpreted and considered with great caution as possible potentialities of this plant source. Therefore, scientific evidence is needed to demonstrate the cause-and-effect relationship of these properties.

T. zebrina (Fig. 1) has widely been used as traditional Chinese medicine for renal system diseases. In Jamaica, high blood pressure, cough and tuberculosis have been treated with this plant. Specifically, the leaves are considered to have beneficial properties to reduce inflammation and treat haemorrhoids and kidney infections. In Mexico, a decoction of the leaves are traditionally consumed as a cold drink called ‘Matali’ [25]. In the Caribbean, leaf extracts are consumed to relieve kidney and urinary problems, and reduce intestinal inflammation [23]. In the past, Filipinos used the leaves as tea to cleanse the blood and relieve influenza symptoms [24]. Malaysians recommended a decoction of the plant to improve kidney function and was believed to have advantages for treating venomous snake bite, leucorrhoea, urinary tract infection, nephritis and bowel inflammation. T. pallida D.R.Hunt has also been traditionally used for its anti-inflammatory and antitoxic potential, as well as improving blood circulation and prevent sore eyes [26]. T. spathacea, also known as Rhoeo spathacea or Rhoeo disccolor, has been used in China in a decoction of dried or fresh leaves and flowers to treat dysentery and haemoptysis [20]. In Singapore, traditional medicinal uses of this plant focus on treating fever, cough, and bronchitis. In spite of all these properties, its sap is considered to have adverse effects related to itching of the skin and eyes, and abdominal and oral pain when ingested [28].

Fig. 1.

T. zebrina. Adapted from https://plants.ces.ncsu.edu/plants/Tradescantia-zebrina/.

These traditional uses may suggest the presence of potential bioactive compounds (in their chemical composition) capable of preventing or alleviating certain diseases. The lack of scientific evidence necessary to prove such applications must be carried out through appropriate scientific methods. Recent studies allow these traditional uses to be translated into future applications of modern medicine.

The therapeutic value and pharmacological effects of medicinal plants largely depend on their phytochemical composition. In the case of Tradescantia, the phytochemical composition has only been explored for a few species. Entire characterization studies are based on phytochemicals qualitative analysis or simple screening of compound families. Phytochemicals quantitative studies in Tradescantia species have not yet been carried out.

Alkaloids, flavonoids, phenolics and saponins have been the most identified phytochemical compounds in Tradescantia species [29, 30, 31, 32]. Apigenin, luteolin and flavonols, 6-hydroxyluteolin and tricin, have been the main identified flavonoids (C-glycosides). The geographical origin of Tradescantia species has been described as a factor that affects the content of these compounds. Lee Tan et al. [33] determined the total phenolic content (TPC), total tannin content (TTC) and total flavonoid content (TFC) of T. spathacea, T. pallida and T. zebrina methanolic extracts (Table 3, Ref. [33]). Cheah. et al. [34] also determined the TPC (33.5 $\pm$ 2.6 mg GAE/g extract) and TFC (9.4 $\pm$ 1.1 mg CE/g extract) of a methanolic extract of T. zebrina leaves.

Del Pero Martínez et al. [35] were the first to qualitatively analyse the flavonoid composition in 42 Tradescantia species. Luteolin, apigenin, 6-hydroxyluteolin and tricin glycosides were the most commonly characterized flavonoids.

Phytochemical screening analyses of T. spathacea leaf extracts showed the presence of coumarins, alkaloids, saponins, flavonoids and terpenoids [31]. In another screening study, alkaloids, steroids, flavonoids, saponins, cardiac glycoside, terpenoids, tannins and phenolic compounds were detected in a T. spathacea leaf extract [29]. Flavonoids, alkaloids, tannins, phenols and steroids were characterized from T. zebrina leaf extracts. T. fuminensis leaf extracts analysis revealed the presence of saponins, phenolic compounds and flavonoids [30, 32]. Huq et al. [36] carried out a phytochemical screening of T. pallida extracts, detecting the presence of alkaloids, tannins and carbohydrates, in high, moderate and trace amounts, respectively. However, no specific metabolites were isolated or identified.

Studies on T. zebrina, T. spathacea and T. albiflora have focused on specifically characterising the phytochemical compounds of the species (Table 4). For example, Dash et al. [22], identified the compounds ecdysone (1), $\beta$-sitosterol (2), 3$\beta$,5$\alpha$,6$\beta$-trihydroxy stigmastrol (3) and succinic acid (4) in T. zebrina (Fig. 2). Various phenolics and carotenoids compounds identified in T. spathacea have been associated to antitumor and/or antioxidant activities [37]. Quoc Hung Vo et al. [38] characterized two new phytochemicals in T. spathacea by NMR and MS: ($\pm$)-tradescantin (5) and tradecantoside. In addition, 14 previously described phytochemical compounds (Nº: 6, 7, 8, 9, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22; Table 4, Fig. 2) were characterized in this study by spectroscopic data comparison. Lee Tan et al. [39], identified four phenolic compounds (epigallocatechin (25), rhoeonoin (26), peltatoside (27) and rutin (28)) in T. spathacea leaves by HPLC-DAD-MS. In a study based on HPLC-DAD-TOF-MS, García-Varela et al. [40], identified the following metabolites in T. spathacea: rhoeonin (26), ferulic acid (29), vanillic acid (30), glycosylated vanillic acid (31) p-coumaric acid (32), and chlorogenic acid (33).

Fig. 2.

Phytochemical compounds characterized in different T. species (T. zebrina, T. albiflora, T. pallida): 1. ecdysone; 2. $\beta$-sitosterol; 3. 3$\beta$, 5$\alpha$, 6$\beta$-trihydroxy stigmastrol; 4. succinic acid; 5. tradescantin; 6. hydroxytyrosol; 7. protocatechuic acid; 8. oresbiusin A; 9. 2-hydroxy-3${}^{\prime }$,4${}^{\prime }$-dihydroxyacetophenone; 10. 3,4-dihydroxymethylbenzoate; 11. 3-(3${}^{\prime }$,4${}^{\prime }$-dihydroxyphenyl)-butenolide; 12. tradecantoside; 13. (S)-2-hydroxy-3-(4${}^{\prime }$-hydroxyphenyl) propanoic acid; 14. (R)-2-hydroxy-3-(4${}^{\prime }$-hydroxyphenyl) propanoic acid; 15. latifolicinin C; 16. latifolicinin B; 17. latifolicinin A; 18. (6S,9R)-roseoside; 20. (2R,3R)-2,3-dihydroxy-2-methylbutyrolactone; 21. bracteanolide A; 22. 4-(3${}^{\prime }$,4${}^{\prime }$-dihydroxyphenyl)furan-2(5H)-one; 23. bracteanolide B; 24. 5-O-acetyl bracteanolide A; 25. epigallocatechin; 26. rhoenoin; 27. peltatoside; 28. rutin; 29. ferulic acid; 30. vanillic acid; 31. glycosylated vanillic acid; 32. p-coumaric acid; 33. chlorogenic acid; 34. tyrosol; 35. indole-3-aldehyde; 36. 2-phenylacetamide; 37. p-hydroxybenzaldehyde; 38. p-hydroxybenzoic acid; 39. rosmarinosin B; 40. 2$\beta$-hydroxyisololiolide; 41. isololiolide; 42. loliolide; 43. tricin; 44. 3-epicyclomusalenol; 45. 24,25-dihydrocimicifugenol; 46. sitosterol; 47. stigmasterol; 47. 7-ketositosterol; 49. 7-ketostigmasterol; 50. 7-hydroxysitosterol; 51. schottenol; 52. ergosterol peroxide; 53. (6R,7E,9R)-9-hydroxy-4,7-megastigmadien-3-one; 54. (E)-3,5,5-trimethyl-4-(3-oxobut-1-en-1-yl)cyclohex-2-enone; 55. (S)-dehydrovomifoliol; 56. (3R)-3-hydroxy-$\beta$-ionone; 57. N-trans-feruloyltyramine; 58. N-trans-feruloyl-3-methoxytyramine.

Shi et al. [41] found that T. pallida contained two main anthocyanins with natural food colorant potential. One was cyanidin 3,7,3${}^{\prime }$-triglucoside with three ferulic acid and extra terminal glucose molecules, and the remaining compound had similar chemical structure though lacking the glucose terminal unit.

Wang et al. [42] discovered that particular compounds isolated from T. albiflora extracts were able to reduce serum uric acid levels in oxonate-induced rats. The methanol extract of T. albiflora was fractionated successively using different polarities solvents such as hexane, ethyl acetate and n-butanol. Repeated column chromatography of the ethyl acetate extract resulted in the purification of the following twelve aromatic compounds: hydroxytyrosol (6), protocatechuic acid (7), 2-hydroxy-3${}^{\prime }$,4${}^{\prime }$-dihydroxyacetophenone (9), 3,4-dihydroxymethylbenzoate (10), 3-(3${}^{\prime }$,4${}^{\prime }$-dihydroxyphenyl)-butenolide (11), bracteanolide A (21), bracteanolide B (23), tyrosol (34), indole-3-aldehyde (35), 2-phenylacetamide (36), p-hydroxybenzaldehyde (37) and p-hydroxybenzoic acid (38) (Fig. 2). These phytochemicals were characterized by MS and NMR. In a recent study, three new secondary metabolites were characterized in T. albiflora by MS, 1D-NMR and 2D-NMR. These metabolites were two butanolides (5-O-acetyl bracteanolide A (24) and rosmarinosin B (39)), and an apocarotenoid (2$\beta$-hydroxyisololiolide (40)) [43]. In addition, 25 previously known metabolites were also identified in this study (Nº: 5, 22, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57 and 58; Table 4, Fig. 2).

Although crucial, these findings are not sufficient for a general understanding of the phytochemical compounds found in most Tradescantia species. These studies are based on qualitative characterizations, and therefore the concentration levels of these phytochemical compounds in Tradescantia species are currently unknown.

In spite of the large number of existing Tradescantia species, there is still a lack of knowledge regarding their qualitative and quantitative phytochemical composition. Considering the advantages of high-resolution analytical techniques, quantitative and qualitative phytochemical studies are necessary to clarify the cause-effect relationship of the beneficial properties.

The different bioactive properties described for Tradescantia species might be related to their phytochemical composition. For instance, several studies have reported the bioactive properties of epigallocatechin, such as antioxidant, antidiabetic, anti-inflammatory or antitumor activities [44]. Hydroxytyrosol is also a phytochemical compound to which antioxidant, anti-inflammatory, anticancer, antidiabetic or cardioprotective properties, have been described [38]. Much of the bioactive properties of specific compounds present in Tradescantia plants have recently been reviewed by Tan et al. [45], highlighting the following compounds: rutin, epigallocatechin, (6S,9R)-roseoside, kaempferol, oresbiusin A, hydroxytyrosol, protocatechuic acid, latifolicin (A, B and C) and ferulic, vanillic, chlorogenic, and p-coumaric acids. Kaempferol, protocatechuic acid, rutin, epigallocatechin, have been described in other plant sources as antioxidant and anticancer compounds [46]. Although individual compounds may have proven individual bioactive properties, it is also important to consider the bioactive potential of Tradescantia extracts in case of possible synergistic effects between compounds. However, only few studies have been conducted to evaluate the bioactivity of Tradescantia extracts (Table 5, Ref. [30, 32, 33, 34, 37, 39, 43, 47, 48, 49, 50, 51, 52, 53, 54]). The following subsections describe the main studies carried out on the evaluation of the bioactive properties of Tradescantia extracts.

Plants contain many different biologically active substances, some of which have proven healing properties, while others are harmful to human health and cause adverse effects [61]. The latter are usually low molecular weight endogenous toxins or secondary metabolites produced by plants for protection from animals, insects or microorganisms [62]. Plant toxins are generally classified into the following four main groups based on the chemical structure: alkaloids, glycosides, proteins, and saponin glycosides [61, 62]. The presence of phytochemicals in Tradescantia extracts, such as alkaloids, flavonoids, tannins, and phenols, indicate potential toxic properties of plant, although, reports on adverse reactions of compounds from this plant are scarce [22, 32]. This is due to the fact that the harmful effects of herbaceous plants are pourly controlled in comparison to the pharmaceuticals counterpart [63].

According to Filmer et al. [64], Tradescantia spp. belong to the fourth class of toxicity, which means that the juice, sap or thorns of this plant can cause skin rash or irritation. This potential toxicity may be attributed to calcium oxalate crystals found in the parenchymal tissues of the stem, leaves, roots, and flowers [65]. Plants in humid environments can cause the plant cells to secrete these crystals, which can then come into contact with the skin [66]. In December 2019, the FDA’s Poisonous Plant Database listed 5 titles that mention the toxicity of this plant. Only one case of a 32-year-old patient allergic to Tradescantia spp. (T. albifloxia and T. fluminensis) has been confirmed in humans [67]. The patient exhibited an itchy face, throat, and conjunctiva, swollen lips, and dyspnea [68] in addition to previous atopic dermatitis. In a recent study, Wang et al. [69] revealed that a methanolic extract of T. zebrina leaves could induce cytochrome (CYP) 3A4, an enzyme activity that metabolizes drugs in human liver microsomes. Some studies have suggested that T. fluminensis may show adverse effects in dogs, causing allergic reactions (red and itchy skin) [70]. More in vivo studies should be conducted to further confirm the effect of Tradescantia. spp. in the human body system.

Despite these few examples of possible negative effects on human health, these plants have been used in beverage production and in folk medicine. However, the lack of specific information on the negative impact of whole plants or extracts obtained from these plants on human health, it can only be determined that their main bioactive compounds have a negative effect on human health.

The 3-epicyclomusalenol, a phytochemical found in Tradescantia spp., has also been identified as a phytochemical compound of banana (Musa sapientum) [71] and brown algae (Kjellmaniella crassifolia) [72]. According to the Human Metabolome Database (HMDB) (http://www.hmdb.ca/), no side effects data has been reported for this compound. Ergosterol peroxide, also obtained from Ananas comosus (pineapple) and fungus Ganoderma lucidum [73], represents a promising new reagent to overcome drug resistance of tumour cells, though no information on the biological side effects and interactions of this compound have been described. Methyl 3,4-dihydroxybenzoate is an antioxidant polyphenol (found in green tea) that attenuates fluoride toxicity on lung epithelial cells [74]. 4-Hydroxybenzoic acid is a low toxicity, antioxidant capable of stimulating the oestrogenic response in human breast cancer cells [75]. Some phytosterols have been reported to have more or less pronounced cytotoxic effects on normal cells. Despite the fact that $\beta$-sitosterol has been recognized as safe, diarrhoea, nausea and indigestion have been described as common side effects after intake. The use of $\beta$-sitosterol is not recommended in children, whereas in pregnant women this compound should be avoided because of the proven uterine stimulating effects [76]. It is well known that $\beta$-sitosterol should not be used in sitosterolemia, due to the fact that sitosterol and other fats abnormally accumulate in the blood. The most recent results in a mouse model showed that stigmasterol leads to left ventricular dysfunction, cardiac interstitial fibrosis, and macrophage infiltration without atherosclerosis and increased mortality [77]. On the other hand, according to the European Food Safety Authority (EFSA), there is no evidence of mutagenicity or genotoxicity of phytosterols or phytosterol esters and, therefore, stigmasterol-rich plants are not a genotoxicity concern [78].

In conclusion, no relevant toxicological data are available on plants belonging to the genus Tradescantia, though long-term history use in humans show no safety concerns for the oral or oromucosal use of the preparations of these plants are apparent. Based on these plant matrices, further toxicological studies are necessary to establish their safety prior to commercialization of products.

T. zebrina, T. fluminensis, T. spathacea, and T. albiflora are the most widely studied species within the genus Tradescantia. Although research has mainly focused on the phytochemical composition and/or biological activities of Tradescantia species, most of the literature is based on traditional applications, descriptive analyzes, and non-medicinal uses. T. zebrina has been the most commonly studied species within the genus concerning bioactivity.

To develop potential therapeutic applications based on Tradescantia compounds, it is necessary to increase the knowledge regarding the biological mechanisms of action of these compounds. More studies should be conducted to better explore the phytochemical composition both quantitatively and qualitatively, as well as the corresponding tests to examine their bioactive activities. The application of modern approaches, such as genomics, proteomics, metabolomics, and transcriptomics, should be considered for future studies of this genus. Given the large number of species in the genus Tradescantia, a more systematic approach is necessary to ensure data are consistently collected in future studies.

AA, Ascorbic acid; DPPH, 2,2-Diphenyl-1-picrylhydrazyl assay; FIC, ferrous ion chelating; FRAP, ferric reducing antioxidant power assay; FRS, Free radical scavenging; FRP, phenolic ferric reducing power; GAE, Gallic acid equivalent; MS, Mass spectrometry; MTT, 3-(4, 5 dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; NMR, Nuclear magnetic resonance; NRU, neutral red uptake; ORAC, oxygen radical absorbance capacity assay, RE, Rutin equivalent; TAE, Tannic acid equivalent; TEAC, Trolox equivalent antioxidant capacity assay; TFC, total flavonoid content; TPC, total phenolic content; TTC, total tannin content.

MB, CQ, JH-B, ÁF-O, SE-Y, COA, AEM, AO, PB, HA, KT, NB, JMB, SS, KA, AS-C, Mde la LC-G, SHEL, MP, IS, SDD, AFAR, US, RMK, WN.S, JS-R equally contributed to this work. ÁF-O, M de la LC-G, SHEL, AFAR and JS-R. critically reviewed the manuscript. All authors contributed to the editorial changes in the manuscript. All authors read and approved the final manuscript.

Not applicale.

We acknowledged Universiti Putra Malaysia (UPM) for article processing fee payment.

This research received no external funding.

The authors declare no conflict of interest.