Abstract
Background: Combretum caffrum (Eckl. & Zeyh.) Kuntze is a small-to-medium-sized deciduous tree widely used in traditional medicines.
Aim: The current study reviews the botany, ethnopharmacology, phytochemistry and pharmacological properties of C. caffrum.
Setting: The current study provides an overview of the botany and ethnopharmacological properties of C. caffrum.
Method: A search for available information on the botany, chemical constituents and pharmacological properties of C. caffrum was conducted by systematically searching the scientific databases which included ScienceDirect®, PubMed®, Web of Science, SpringerLink®, Google Scholar, SciELO and Scopus®, as well as pre-electronic literature sources such as book chapters, books and other scientific publications obtained from the university library.
Results: The findings highlight the use of C. caffrum as a multipurpose species, providing a wide range of goods and ecosystem services. The bark, leaves, leaf juice, roots, root bark and stem bark of C. caffrum are used as charm for harming an enemy and tonic, as ethnoveterinary medicine and also as traditional medicine for body and leg pains, cancer and eye problems. Chemical compounds identified from C. caffrum include flavonoids, phenanthrene, phytosterols, stilbenoids, polyphenolics, iridoids, lignans, ketones, glycosides, fatty acids, xanthones, coumarins, tannins and triterpenoids. The crude extracts of C. caffrum and phytochemical compounds isolated from the species exhibited anticancer, antibacterial, antifungal, antiviral, antioxidant and cytotoxicity activities.
Contribution: This study adds to existing literature information about the botany, ethnopharmacology, phytochemistry and pharmacological properties of C. caffrum. To realise the full potential of C. caffrum as a valuable component of traditional pharmacopoeia, future studies should explore the active ingredients of the species using various in vitro and in vivo assays.
Keywords: bush willow family; Combretaceae; Combretum caffrum; materia medica; traditional medicine.
Introduction
Combretum caffrum (Eckl. & Zeyh.) Kuntze (Figure 1) is a member of the Combretaceae family commonly known as the white mangrove, Indian almond or bush willow. The Combretaceae family comprises approximately 10 genera and 530 species, which are mainly trees, shrubs, shrublets or lianas with subherbaceous forms being rare (Christenhusz & Byng 2016; Jordaan, Van Wyk & Maurin 2011; Raj, Solomon & Thangaraj 2022). Members of this family exhibit a pantropical distribution, with a few species extending into warm temperate regions. They are found in diverse habitats, including coastal scrub, savanna, grassland, rainforest, woodland, littoral and mangrove vegetation (Gere et al. 2015; Turner 2020).
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FIGURE 1: C. caffrum (Eckl. & Zeyh.) Kuntze: The branches show leaves and fruits. |
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Over the past five decades, there has been a notable increase in the evaluation of the ethnopharmacological properties of Combretum species, as highlighted in a review by Rogers and Verotta (1996). Several Combretum species that have been used for generations as sources of traditional remedies are known to have therapeutic healing properties and valued as materia medica in tropical Africa, including C. caffrum, C. adenogonium Steud. ex A.Rich., C. albopunctatum Suess., C. apiculatum Sond., C. celastroides Welw. ex M.A.Lawson, C. coccineum (Sonn.) Lam., C. collinum Fresen, C. comosum G.Don, C. erythrophyllum (Burch.) Sond., C. hereroense Schinz, C. imberbe Wawra, C. indicum (L.) DeFilipps, C. kraussii Hochst., C. micranthum G.Don, C. molle R.Br. ex G.Don, C. mossambicense (Klotzsch) Engl., C. mucronatum Schumach. & Thonn., C. padoides Engl. & Diels, C. paniculatum Vent., C. platypterum (Welw.) Hutch. & Dalziel and C. zeyheri Sond. (Burkill 1994; Hutchings et al. 1996; Neuwinger 2000; Schmelzer & Gurib-Fakim 2013).
Combretum caffr um has notable commercial potential as medicinal plant because a patent for use of combretastatins and the combretastatin derivatives isolated from the species against cancer was filed at the United States Patent and Trademark Office (Pettit & Singh 1991). A subsequent patent by Liu (2012), outlining protocols required for producing high yields of combretastatin from C. caffrum, gained attention from the media over the past 10 years. Similarly, combretastatin A-4 analogues, AVE8062 and CA-4P, have been approved by the European Medicines Agency and US Food and Drug Administration (FDA) for treating gliomas, anaplastic thyroid cancer (ATC), neuroendocrine tumours, ovarian cancer and gastro-enteropancreatic neuroendocrine tumours (Patel et al. 2024). Therefore, this article provides a comprehensive review of the importance of C. caffrum in traditional medicine with a holistic approach that covers its botany, chemical constituents and pharmacological properties.
Methods
A search for available information on the botany, chemical constituents and pharmacological properties of C. caffrum was conducted by systematically searching the scientific databases, including ScienceDirect®, PubMed®, Web of Science, SpringerLink®, Google Scholar, SciELO and Scopus®, as well as pre-electronic literature sources, such as book chapters, books and other scientific publications obtained from the university library. The search was conducted from September to December 2024, using the following keywords: ‘Combretum caffrum’; its synonyms including ‘C. dregeanum C.Presl’, ‘C. salicifolium E.Mey. ex Hook.’ and ‘Dodonaea caffra Eckl. & Zeyh.’, ‘D. conglomerata Eckl. & Zeyh.’ and English common names such as ‘African bush willow’, ‘African willow tree’, ‘bush willow’, ‘bush willow tree’, ‘bushveld willow’ and ‘Cape bush willow’. An additional search was conducted using the keywords ‘biological activities of C. caffrum’, ‘pharmacological properties of C. caffrum’, ‘ethnobotany of C. caffrum’, ‘medicinal uses of C. caffrum’, ‘phytochemistry of C. caffrum’ and ‘traditional uses of C. caffrum’. The search covered publications from 1962 to 2024, a long period to capture literature on the botany, chemical constituents and the pharmacological properties of C. caffrum.
Ethical considerations
The ethical waiver to conduct this study was obtained from the University of Fort Hare Department of Biotechnology and Biological Sciences dated 15 February 2025.
Review findings
Taxonomy and morphological description of C. caffrum
The genus Combretum consists of approximately 276 species with a pantropical distribution, mainly in tropical Asia and Africa, but absent in the Pacific Islands and most of Australia (Boon, Jordaan & Van Wyk 2020; Stace 2007). About 140 species have been recorded in tropical Africa and approximately 20 species are endemic to Madagascar (Schmelzer & Gurib-Fakim 2013). Therefore, the highest number of Combretum species occur in tropical Africa, with the centre of diversity of the genus on the African continent (Boon et al. 2020; Stace 2007). The genus Combretum comprises trees, shrubs and lianas characterised by leaves that are opposite, whorled or rarely alternate, with entire margins, lacking stipules or having very small stipules, and with persistent petioles that often form hooked spines (Boon et al. 2020). The flowers are bisexual, actinomorphic, with an inferior ovary and winged fruits, or rarely an unwinged nut (Boon et al. 2020). The genus name ‘Combretum’ is of classical origin, as the name was first used by the Roman naturalist, natural philosopher, naval and military commander Gaius Plinius Secundus, known in English as Pliny (23 – 79 AD), used in reference to an unknown plant (Palmer & Pitman 1972; Schmidt et al. 2017; Venter & Venter 2015). The name was later reused by the Swedish botanist Pehr Löfling (31 January 1729 – 22 February 1756) for the Combretum genus (Palmer & Pitman 1972; Schmidt et al. 2017; Venter & Venter 2015). The specific species name ‘caffrum’ was derived from the Arabic or Hebrew word ‘kafir’, ‘kaffir’, ‘kafri’ or ‘kaffraria’, meaning ‘person living on the land’. This name is often applied to plant species that naturally occur in the eastern region or the Eastern Cape province of South Africa (Glen 2004; Palmer & Pitman 1972). The common name ‘bush willow’ indicates a superficial resemblance to willows, that is, species belonging to the genus Salix L. (family Salicaceae); but ‘bush willows’ and ‘willows’ are not closely related to each other (Palmer & Pitman 1972). Other common names of the species included ‘African bush willow’, ‘African willow tree’, ‘bush willow tree’, ‘bushveld willow’ and ‘Cape bush willow’. Synonyms for the species are ‘C. dregeanum C.Presl’, ‘C. salicifolium E.Mey. ex Hook.’, ‘Dodonaea caffra Eckl. & Zeyh.’ and ‘D. conglomerata Eckl. & Zeyh.’ (Germishuizen & Meyer 2003; Jordaan et al. 2011; Palmer & Pitman 1972).
Combretum caffrum is a small-to-medium-sized deciduous shrub or spreading tree reaching 10 metres in height (Germishuizen & Meyer 2003; Palgrave 2002; Palmer & Pitman 1972). The bark is pale grey to greyish-brown in colour. The leaves are usually opposite, subopposite or sometimes alternate, borne on flattish stalks. The leaves are narrowly elliptic or lanceolate, narrowing from the middle to both ends, bluntly or sharply pointed (Figure 1), with the margins untoothed, slightly in-rolled and often faintly waxy. When young, the leaves are often scaly and hairy, and when matured, they are grey or shiny green and smooth above, and paler, hairless and scaly below. The flowers are bisexual, regular, whitish or yellowish and borne singly in the axils of the leaves. The fruits are winged nuts, lime-green when young, and shiny, tinged pink and reddish upon ripening (Figure 1). Combretum caffrum is endemic to the Eastern Cape province in South Africa, occurring at an altitude ranging from 15 m to 762 m above the sea level (Germishuizen & Meyer 2003). Combretum caffrum has been recorded along river and stream banks, in watercourses or near water and in moist areas in the grasslands, thickets and forests (Palgrave 2002; Palmer & Pitman 1972). Combretum caffrum is seldom found far from water and is a common sight with its crooked, light-coloured stem and thick, drooping, willow-like foliage, overhanging streams or in damp spots (Palmer & Pitman 1972). Morphologically, Combretum caffrum is similar to C. erythrophyllum (Burch.) Sond., a species recorded in Botswana, Eswatini, Mozambique, Namibia, South Africa and Zimbabwe (Exell 1978; Germishuizen & Meyer 2003). In the Eastern Cape province of South Africa, where both species may grow in the same habitat, they can be distinguished by leaf shape and fruit colouration. C. caffrum is characterised by narrowly elliptic to lanceolate leaves that are hairless and by fruits that are usually tinged pink or reddish upon ripening (Jordaan et al. 2011; Van Wyk & Van Wyk 2013).
Traditional uses of C. caffrum
Combretum caffrum is categorised as a multipurpose species in the Eastern Cape province of South Africa. The species is widely collected from the wild for firewood, charms and/or ritual purposes, fencing poles, medicinal uses and as a source of timber (Cocks & Wiersum 2003). The wood of C. caffrum is bright yellow, hard, heavy, strong and compact, but not so durable as it is prone to rotting and also is susceptible to borer attacks (Maroyi 2013). Honeybees often collect nectar and pollens from the flowers of C. caffrum, and the honey obtained from the species is bitter but produces no harmful effects (Hutchings et al. 1996; Watt & Breyer-Brandwijk 1962). Combretum caffrum is an attractive shrub or tree, popular in private gardens, as it tolerates frost and moderate drought and is widely cultivated outside its natural distribution range (Palmer & Pitman 1972). It is valued for providing shade (Palmer & Pitman 1972) and the trees are often left in agricultural fields as shade trees (Maroyi 2013). Combretum caffrum is also traded as an ornamental tree in South Africa, the United States of America and Australia (Maroyi 2013).
Combretum caffrum is a potential forage species for ruminants, particularly livestock species such as cattle and goats, and is also used in game feeding (Tefera & Mlambo 2017). No information could be found in the literature regarding the digestibility value of the leaves, branches, twigs or fruits of C. caffrum for livestock or game. However, research conducted by Tefera and Mlambo (2017) and Mathipa, Mphosi and Masoko (2022) showed that C. caffrum is a good source of proteins, energy, and minerals such as calcium, copper, iron, magnesium, manganese, phosphorus, potassium, sodium and zinc (Table 1). The protein content of C. caffrum ranging from 6.0% to 13.0% suggests that its browse value is higher than that of other Combretum species such as C. imberbe that have leaves and twigs containing only 4.0% protein (McGregor 1991). Although C. caffrum is deciduous, the species is known to exhibit a long leaf-retention period (Palmer & Pitman 1972) and, therefore, the species could be used as a supplement, particularly in ruminant feed. Fodder trees such as C. caffrum are important feed sources for both livestock and game in a wide range of agricultural systems worldwide. Such species are important sources of micro- and macro-elements as well as essential nutrients such as proteins and energy (Geng et al. 2020).
| TABLE 1: Proximate, mineral and trace metals composition of ashes, leaves and stems of C. caffrum. |
Several ethnobotanical and ethnopharmacological publications cite the uses of bark, leaves, roots, root bark and stem bark of C. caffrum as a charm for harming an enemy and as a tonic, and also as a traditional medicine for body and leg pains, cancer and eye problems (Table 2). The bark, leaf juice, leaves and stem bark are used as ethnoveterinary medicine for conjunctivitis and redwater in livestock (Afolayan et al. 2002; Maposa et al. 2010; Maroyi 2013; Masika & Afolayan 2003; Masika, Van Averbeke & Sonandi 2000; McGaw & Eloff 2008). The Zulu people in the KwaZulu-Natal province of South Africa use C. caffrum extract as a spear poison for hunting purposes (Hutchings et al. 1996; Watt & Breyer-Brandwijk 1962). C. caffrum is an important component of the South African traditional pharmacopoeia and, therefore, the species is included in medicinal monographs, such as ‘Medicinal and Magical Plants of Southern Africa: An Annotated Checklist’ and ‘Medicinal Plants of South Africa’, written by Arnold et al. (2002) and Van Wyk et al. (2013), respectively. Similarly, the bark, leaves and roots of C. caffrum are sold in informal herbal medicine markets as sources of traditional medicines in South Africa (Maroyi 2013; Williams, Balkwill & Witkowski 2001). A herbal concoction prepared from the bark decoction of C. caffrum is sold in informal herbal medicine markets in South Africa as an anticancer remedy (Cunningham 1990; Maroyi 2013). Van Wyk and Wink (2017) argued that C. caffrum is a ‘commercialised medicinal plant’ since the bark of the species is the major source of numerous phenanthrenes and stilbenoids, such as combretastatin A-4 and its derivatives, which are renowned for their strong anticancerous properties.
Phytochemistry and pharmacological properties of C. caffrum
Qualitative and quantitative phytochemical analyses of C. caffrum fruits, leaves, stems, stem wood and twigs have revealed the presence of various bioactive compounds, including flavonoids, phenanthrene, phytosterols, stilbenoids, polyphenolics, iridoids, lignans, ketones, glycosides, fatty acids, xanthones, coumarins, tannins and triterpenoids (Table 3) (El-Zayat et al. 1993; Kovács, Vasas & Hohmann 2008; Mariri et al. 2023; Mariri, Mongalo & Makhafola 2024; Pettit, Cragg & Singh 1987a; Pettit et al. 1982, 1987b, 1988a, 1988b, 1995; Pettit & Singh 1987). Some of the phytochemical compounds isolated from C. caffrum and its crude extracts exhibited anticancer, antibacterial, antifungal, antiviral, antioxidant and cytotoxic activities, supporting its traditional medicinal uses.
| TABLE 3: Phytochemical composition of C. caffrum. |
Antibacterial activities
Eloff (1999) evaluated the antibacterial activities of acetone extracts of C. caffrum leaves against Escherichia coli, Staphylococcus aureus, Enterococcus faecalis and Pseudomonas aeruginosa using the two-fold serial dilution method, with gentamicin as a positive control. The extracts exhibited activities against the tested pathogens with minimum inhibitory concentration (MIC) values ranging from 0.04 mg/mL to 6.0 mg/mL (Eloff 1999). Masika and Afolayan (2002) evaluated the antibacterial activities of acetone, methanol and water extracts of C. caffrum bark against Bacillus cereus, Bacillus subtilis, Bacillus pumilus, Micrococcus kristinae, Klebsiella pneumoniae, Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Enterobacter cloacae and Serratia marcescens using the microdilution method. The extracts exhibited activities against the tested pathogens exhibiting MIC values ranging from 0.5 mg/mL to 5.0 mg/mL (Masika & Afolayan 2002). Anokwuru et al. (2021) evaluated the antibacterial activities of methanol extracts of C. caffrum leaves against Staphylococcus aureus, Staphylococcus epidermidis, Bacillus cereus, Staphylococcus epidermidis, Klebsiella pneumoniae, Enterococcus faecalis, Pseudomonas aeruginosa, Escherichia coli, Salmonella typhimurium and Shigella sonnei using the microdilution assay with ciprofloxacin as a positive control. The extracts exhibited activities against the tested pathogens, with MIC values ranging from 0.25 mg/mL to > 3.0 mg/mL (Anokwuru et al. 2021).
Antifungal activities
Afolayan et al. (2002) evaluated the antifungal activities of acetone extracts of C. caffrum bark against Aspergillus niger, Alternaria alternaria, Mucor hiemalis, Schizophyllum commune and Penicillium notatum using the agar dilution assay. The extracts were fungicidal at a concentration of 10.0 mg/mL and exhibited inhibition against the tested pathogens with inhibition values ranging from 49.3% to 100.0% and the median lethal concentration (LC50) values ranging from 1.8 mg/mL to > 10.0 mg/mL (Afolayan et al. 2002). Masika and Afolayan (2002) evaluated the antifungal activities of acetone and methanol extracts of C. caffrum bark against Aspergillus alternaria, Aspergillus niger, Mucor hiemalis, Penicillium notatum and Schizophyllum commune using the agar dilution method. At 10.0 mg/mL, the extracts exhibited activities against the tested pathogens, exhibiting inhibition values that range from 49.3% to 100.0% (Masika & Afolayan 2002). Masoko, Picard and Eloff (2007) evaluated the antifungal activities of hexane, acetone, methanol and dichloromethane extracts of C. caffrum leaves against Candida albicans, Aspergillus fumigatus, Cryptococcus neoformans, Sporothrix schenckii and Microsporum canis using the microdilution assay, with amphotericin B as a positive control. The extracts exhibited activities against the tested pathogens, with MIC values ranging from 0.02 mg/mL to > 2.5 mg/mL (Masoko et al. 2007). Dikhoba et al. (2019) evaluated the antifungal activities of acetone extracts of C. caffrum leaves against Aspergillus ochraceous, Aspergillus flavus and Fusarium verticillioides using the microplate dilution method, with amphotericin B as a positive control. The extracts exhibited activities against the tested pathogens, with MIC values ranging from 0.16 mg/mL to 0.63 mg/mL (Dikhoba et al. 2019). Mariri et al. (2023) evaluated the antifungal activities of methanol extracts of C. caffrum leaves against Aspergillus parasiticus, Cladosporium cladosporioides, Aspergillus nomius, Penicillium haloterans, Fusarium verticilloides, Fusarium oxysporum and Fusarium graminearum using the microdilution broth assay, with amphotericin B, propiconazole and tebuconazole as positive controls. The extract exhibited activities against the tested pathogens, with MIC values ranging from 0.16 mg/mL to 1.25 mg/mL (Mariri et al. 2023).
Antiviral activities
McGaw et al. (2009) evaluated the antiviral activities of acetone extract of C. caffrum leaves against the sensitive feline herpesvirus type 1 using an in vitro antiviral assay. The extract demonstrated promising activities exhibiting viral cytopathic effects (McGaw et al. 2009).
Antioxidant activities
Masoko and Eloff (2007) evaluated the antioxidant activities of acetone and methanol extracts of C. caffrum leaves using 2,2-diphenyl-1-picryl hydrazyl (DPPH) free radical scavenging assay. The extract exhibited moderate antioxidant activities (Masoko & Eloff 2007). Dikhoba et al. (2019) evaluated the antioxidant activities of acetone extracts of C. caffrum leaves using the DPPH and 2,2′-azinobis (3-ethylbenzthiazoline-6-suphonic acid) (ABTS) free radical scavenging assays, with levo-ascorbic acid as a positive control. The extracts exhibited activities against ABTS and DPPH with half-maximal inhibitory concentration (IC50) values of 0.01 mg/mL and 0.07 mg/mL, respectively (Dikhoba et al. 2019). Mathipa et al. (2022) evaluated the antioxidant activities of 70% acetone extracts of C. caffrum leaves and stems using the DPPH free radical scavenging assay, with levo-ascorbic acid as a positive control. The extracts exhibited dose-dependent activities with scavenging activities ranging from 60.0% to 80.0% (Mathipa et al. 2022). Mariri et al. (2023) evaluated the antioxidant activities of methanol extracts of C. caffrum leaves using the ABTS and DPPH free radical scavenging assays, with levo-ascorbic acid as a positive control. The extract exhibited antioxidant activities with IC50 values of 10.0 μg/mL and 70.0 μg/mL against DPPH and ABTS, respectively (Mariri et al. 2023).
Anticancer activities
Pettit et al. (1982) evaluated the anticancer activities of the phytochemical compound combretastatin A-4 isolated from C. caffrum branches, fruits and leaves against the murine P-388 lymphocytic leukaemia using the in vitro astrocytoma bioassay. The phytochemical compound inhibited murine P-388 lymphocytic leukaemia cell growth demonstrating the median effective dose (ED50) value of 1.0 μg/mL (Pettit et al. 1982). Other phytochemical compounds isolated from C. caffrum that showed potent in vitro and in vivo activities in the P-388 lymphocytic leukaemia bioassay include combretastatin A-1, 6,7-dihydroxy-2,3,4-trimethoxy-9,10-dihydrophenanthrene, combretastatin B-3, 7-hydroxy-2.3,4,6-tetramethoxyphenanthrene, combretastatin B-4, 2,7-dihydroxy-3,4,6-trimethox-9,10 dihydrophenanthrene, bibenzyls 7, 8 and 9, and 7-hydroxy-2.3,4,6-tetramethox-9,10-dihydrophenanthrene (El-Zayat et al. 1993; Pettit et al. 1987a, 1988a, 1988b). On the other hand, combretastatin A-4 and A-1 are the most potent compounds, which exhibited in vitro and in vivo efficacy in a wide variety of tumour cell types (Kingston 2009; Singh 2024).
Cytotoxic activities
McGaw, Elgorashi and Eloff (2010) evaluated the cytotoxic activities of acetone extracts of C. caffrum leaves against bovine dermis cells and Vero kidney cells. The extracts demonstrated activities against both cell types exhibiting LC50 values which were < 50.0 μg/mL (McGaw et al. 2010). Mariri et al. (2024) evaluated the cytotoxic activities of methanol extracts of C. caffrum leaves against the African green monkey kidney (Vero) cells and the human colorectal adenocarcinoma cell line (Caco-2) using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide colorimetric assay. The extract was cytotoxic to Vero cells at 500.0 μg/mL and demonstrated cytotoxic activities against Caco-2 cells in a dose-dependent manner (Mariri et al. 2024).
Conclusion
As outlined in the present review, C. caffrum is characterised by important and diverse values as a multipurpose species. While extensive evaluations of combretastatins have been undertaken, the ethnobotanical knowledge of the species has not been properly studied. To realise the full potential of C. caffrum, future studies should explore additional active anti-tumour phytochemical compounds using various in vitro and in vivo models. Such extensive research can make a valuable contribution to the growing knowledge about C. caffrum and its active ingredients, and this could potentially lead to the commercial development of anti-tumour pharmaceutical and cosmetic products.
Acknowledgements
Competing interests
The author declares that they have no financial or personal relationships that may have inappropriately influenced them in writing this article.
Author’s contributions
A.M. declares that they are the sole author of this article.
Funding information
This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors.
Data availability
Data sharing is not applicable to this article as no new data were created or analysed in this study.
Disclaimer
The views and opinions expressed in this article are those of the author and are the product of professional research. It does not necessarily reflect the official policy or position of any affiliated institution, funder, agency or that of the publisher. The author is responsible for this article’s results, findings and content.
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