Medicinal Uses of the Fabaceae Family in Zimbabwe: A Review

The current study is aimed at providing a systematic review of the ethnomedicinal, phytochemical and pharmacological properties of Fabaceae species used as sources of traditional medicinies in Zimbabwe. Fabaceae is one of the well-known plant families of ethnopharmacological importance. Of the approximately 665 species of the Fabaceae family occurring in Zimbabwe, about 101 are used for medicinal purposes. Many communities in the country, mainly in peri-urban, rural and marginalized areas with limited access to healthcare facilities, rely on traditional medicines as their primary healthcare. The study reviewed research studies undertaken on Zimbabwe’s Fabaceae species during 1959 to 2022. Information was gathered from literature sourced from Google Scholar, Science Direct, Scopus, PubMed, books, dissertations, theses and scientific reports. This study showed that 101 species are traditionally used to manage human and animal diseases in Zimbabwe. The genera with the highest number of medicinal uses are Indigofera, Senna, Albizia, Rhynchosia and Vachellia. Species of these genera are used as traditional medicines against 134 medical conditions, mainly gastrointestinal conditions, female reproductive conditions, respiratory conditions and sexually transmitted infections. Shrubs (39.0%), trees (37.0%) and herbs (18.0%) are the primary sources of traditional medicines, while roots (80.2%), leaves (36.6%), bark (27.7%) and fruits (8.9%) are the most widely used plant parts. Many of Zimbabwe’s Fabaceae species used as sources of traditional medicines have been assessed for their phytochemical and pharmacological properties, corroborating their medicinal uses. However, there is a need to unravel the therapeutic potential of the family through further ethnopharmacological research focusing on toxicological studies, in vitro and in vivo models, biochemical assays and pharmacokinetic studies.


Introduction
The Fabaceae (Leguminosae), often referred to as the bean, legume or pea family, is the third largest plant family after the Asteraceae and Orchidaceae in terms of plant species numbers [1]. The Fabaceae family consists of approximately 770 genera and 19,500 species [1,2] recorded in almost all of the biomes in the world except Antarctica and the high Arctic [3]. Research has shown that the success of the family in dominating in several hospitable and disturbed habitats is ascribed to the ability of the species to fix atmospheric nitrogen, thus allowing the plant species to grow in nutrient-poor soils [4][5][6]. Recent morphological and molecular research has supported that the Fabaceae family is a monophyletic family [2,7]. However, the Fabaceae family is divided into six subfamilies, namely the Caesalpinioideae (148 genera and 4400 species), Cercidoideae (12 genera and 335 species), Detarioideae (84 genera and 760 species), Dialiodeae (17 genera and 85 species), Duparquetioideae (monotypic genus) and Faboideae (or Papilionoideae) (503 genera and 14,000 species) [2]. Members of the Fabaceae family include trees, shrubs, subshrubs, woody lianas, climbing annuals, herbs and aquatics [8]. The flowers are asymmetric, bilaterally symmetric or radially symmetric, and are pollinated by bats, birds and insects [9]. The leaves of the majority of species belonging to the Fabaceae family are compound, doublecompound or trifoliolate, sometimes with a swollen leaf base, a superior ovary with one locular, and the fruit is usually a two-valved, dehiscent pod that is rarely fleshy but is sometimes indehiscent and occasionally breaking into segments [10,11].
The majority of the members of the Fabaceae family are culturally and economically important throughout the world, and are used as sources of traditional medicines, food, timber, garden ornamentals, dyes, fibres, fuels, gums and insecticides [6,12,13]. The role played by Fabaceae species in the provision of ecosystem services and goods that support human wellbeing and survival have been highlighted in some studies conducted in different countries of the world [14,15]. Many members of this family have been widely studied for their bioactive chemical constituents such as phenolic acids, flavonoids, lectins, saponins, alkaloids and carotenoids [16]. Pharmacological studies have shown that some species exhibit potent anticancer, antioxidant, antimicrobial, anti-inflammatory, analgesic, antiulcer, antidiabetic, antirheumatic, cytotoxic and antiparasitic activities, among others [16][17][18]. Therefore, extensive phytochemical and pharmacological evaluations of some of the utilized Fabaceae species may lead to the discovery and development of novel pharmaceutical products, functional food ingredients and cosmetic products. Despite the discovery of several secondary metabolites in the Fabaceae, this family has attracted disproportionately little attention in the context of ethnopharmacological research. It is, therefore, within this context that this study was undertaken, with the aim of exploring and documenting the ethnomedicinal knowledge of Zimbabwe. Such a synthesis identified the gaps in knowledge on the therapeutic potential of the Fabaceae species and may also provide helpful information on ethnopharmacological research areas that require further research.

Materials and Methods
A literature search on Fabaceae species used as traditional medicines in Zimbabwe was conducted from September 2021 to November 2022. This information was retrieved from different online databases such as BioMed Central, Web of Science, Springerlink, Google Scholar, Scielo, PubMed, Science Direct, ACS Publications, Scopus and JSTOR. In addition, theses, dissertations, book chapters, books and scientific reports were retrieved from the libraries of the University of Fort Hare (UFH) in South Africa and the National Herbarium (SRGH) in Harare, Zimbabwe. Keywords and terminologies such as Zimbabwe, ethnobotany, ethnomedicine, ethnopharmacology, indigenous, medicine, phytomedicine, traditional medicine, Zimbabwean Fabaceae, Zimbabwean Leguminosae, medicinal Fabaceae, medicinal Leguminosae, Zimbabwean traditional medicine, Fabaceae and Leguminosae were used to search for relevant articles as shown in the PRISMA flow diagram ( Figure 1). From each article, the following information was collected: the scientific names of the plant species, their growth form, plant part(s) used, methods of preparation and medicinal uses. The medicinal use categories were classified according to the Economic Botany Data Collection Standard [19]. The scientific names of the Fabaceae species from the original data sources were updated to the recently accepted names according to the Plants of the World Online website [20]. The Fabaceae subfamilies were updated following the classifications of the "Legume Phylogeny Working Group", which presently recognizes six subfamilies: Caesalpinioideae, Cercidoideae, Detarioideae, Dialioideae, Duparquetioideae and Papilionoideae [2].

Medicinal Plant Diversity
This study recorded 101 species traditionally used to manage and treat human and animal diseases in Zimbabwe (Table 1). Of these, 91 species are indigenous to Zimbabwe (90.1%), while nine species are exotic (8.9%), either naturalized as weeds or cultivated in home gardens and agricultural fields as ornamentals, fodder or food plants. The subfamilies Caesalpinoideae and Faboideae are dominant, with 54 species (53.5%) and 55 species (54.5%), respectively, and the remaining two species belonging to the Cercidoideae. Therefore, 101 species (15.2%) out of 665 species of the Fabaceae family known to occur in Zimbabwe [21] are used as sources of traditional medicines. A similar study by Van Wyk [6] showed that 338 species out of 1748 Fabaceae species (19.3%) are used as traditional medicines in southern Africa. Similar findings have been reported in Thailand, where 261 species out of 688 Fabaceae species are used as sources of traditional medicines [22]. Macêdo et al. [23] and Sutjaritjai et al. [24] argued that the prominence of Fabaceae taxa in traditional pharmacopoeia throughout the world is possibly associated with the wide distribution of the family, as the different growth forms of the species grow in many types of habitats and vegetation, and therefore are available in all seasons.

Medicinal Plant Diversity
This study recorded 101 species traditionally used to manage and treat human and animal diseases in Zimbabwe (Table 1). Of these, 91 species are indigenous to Zimbabwe (90.1%), while nine species are exotic (8.9%), either naturalized as weeds or cultivated in home gardens and agricultural fields as ornamentals, fodder or food plants. The subfamilies Caesalpinoideae and Faboideae are dominant, with 54 species (53.5%) and 55 species (54.5%), respectively, and the remaining two species belonging to the Cercidoideae. Therefore, 101 species (15.2%) out of 665 species of the Fabaceae family known to occur in Zimbabwe [21] are used as sources of traditional medicines. A similar study by Van Wyk [6] showed that 338 species out of 1748 Fabaceae species (19.3%) are used as traditional medicines in southern Africa. Similar findings have been reported in Thailand, where 261 species out of 688 Fabaceae species are used as sources of traditional medicines [22]. Macêdo et al. [23] and Sutjaritjai et al. [24] argued that the prominence of Fabaceae taxa in traditional pharmacopoeia throughout the world is possibly associated with the wide distribution of the family, as the different growth forms of the species grow in many types of habitats and vegetation, and therefore are available in all seasons.   Indigofera is the genus with the highest number of medicinal Fabaceae species (12 species), followed by Senna (six species), and Albizia, Rhynchosia and Vachellia with five species each ( Figure 2). However, the genera associated with the highest number of records in the literature are Elephantorrhiza (12 records), Pterocarpus (11 records), Senna (10 records), Albizia and Erythrina (nine records each) and Vachellia with eight records (Figure 2). The number of medicinal species found in each genus is significantly correlated to the total number of species in each genus in Zimbabwe (p < 0.01, r = 0.772). These results are consistent with those observed by Anorld et al. [49], who recorded 11 medicinal species of Albizia, followed by Rhynchosia (12 species), Senna (17 species), and Indigofera and Vachellia with 32 species each. In Botswana, Hedberg and Staugård [50] argued that one Senna species, followed by Albizia (three species), Rhynchosia (four species), Indigofera (five species) and Vachellia (six species) were used as traditional medicines in that country. Moreover, several species of Albizia, Elephantorrhiza, Erythrina, Senna and Vachellia are included in the monograph Medicinal Plants of South Africa, with detailed information on their botany, medicinal uses, preparation, dosage, active ingredients and pharmacological effects [51]. E.P.Sousa roots stomach problems, toothache, venereal diseases, wounds and ethnoveterinary medicine Zornia glochidiata Rchb. ex DC. 1 Herb Roots Dilating the birth canal, preventing abortion and venereal diseases 1 [25] * = Exotic; # = cultivated or collected from semi-natural landscapes; + = Fabaceae subfamilies: 1 = Faboideae, 2 = Caesalpinoideae, 3 = Cercidoideae.
Indigofera is the genus with the highest number of medicinal Fabaceae species (12 species), followed by Senna (six species), and Albizia, Rhynchosia and Vachellia with five species each ( Figure 2). However, the genera associated with the highest number of records in the literature are Elephantorrhiza (12 records), Pterocarpus (11 records), Senna (10 records), Albizia and Erythrina (nine records each) and Vachellia with eight records ( Figure  2). The number of medicinal species found in each genus is significantly correlated to the total number of species in each genus in Zimbabwe (p < 0.01, r = 0.772). These results are consistent with those observed by Anorld et al. [49], who recorded 11 medicinal species of Albizia, followed by Rhynchosia (12 species), Senna (17 species), and Indigofera and Vachellia with 32 species each. In Botswana, Hedberg and Staugård [50] argued that one Senna species, followed by Albizia (three species), Rhynchosia (four species), Indigofera (five species) and Vachellia (six species) were used as traditional medicines in that country. Moreover, several species of Albizia, Elephantorrhiza, Erythrina, Senna and Vachellia are included in the monograph Medicinal Plants of South Africa, with detailed information on their botany, medicinal uses, preparation, dosage, active ingredients and pharmacological effects [51].

Growth Habit and Parts Used
Shrubs (39.0%), followed by trees (37.0%) and herbs (18.0%), are the primary sources of the medicinal Fabaceae species in Zimbabwe ( Figure 3A). The plant parts used for traditional medicine preparations include bark, bark fibre, bark sap, bulbs, charcoal, fibre, flowers, fruits, leaves, pods, rhizomes, roots, root bark, root sap, sap, seeds, tubers and twigs ( Table 1). The roots are the most frequently used (81 species), followed by leaves (37 species), bark (28 species), fruits (nine species), seeds (four species), twigs (three species) and tubers (two species), with the rest of the plant parts represented by a single species each ( Figure 3B). However, harvesting the roots of herbaceous plants for medicinal purposes is not sustainable, as it threatens the survival of these plants used to treat human and animal diseases. It is well recognized by conservationists that medicinal plants primarily valued for their roots and those which are intensively harvested for their bark often tend to be the most threatened by overexploitation [52,53]. Afzelia quanzensis, Baikiaea plurijuga, Dalbergia melanoxylon and Pterocarpus angolensis are listed in the Zimbabwean Red Data List, as these four species are threatened with extinction mainly due to overexploitation as sources of timber for construction or wood carving [54].
of the medicinal Fabaceae species in Zimbabwe ( Figure 3A). The plant parts used for traditional medicine preparations include bark, bark fibre, bark sap, bulbs, charcoal, fibre, flowers, fruits, leaves, pods, rhizomes, roots, root bark, root sap, sap, seeds, tubers and twigs ( Table 1). The roots are the most frequently used (81 species), followed by leaves (37 species), bark (28 species), fruits (nine species), seeds (four species), twigs (three species) and tubers (two species), with the rest of the plant parts represented by a single species each ( Figure 3B). However, harvesting the roots of herbaceous plants for medicinal purposes is not sustainable, as it threatens the survival of these plants used to treat human and animal diseases. It is well recognized by conservationists that medicinal plants primarily valued for their roots and those which are intensively harvested for their bark often tend to be the most threatened by overexploitation [52,53]. Afzelia quanzensis, Baikiaea plurijuga, Dalbergia melanoxylon and Pterocarpus angolensis are listed in the Zimbabwean Red Data List, as these four species are threatened with extinction mainly due to overexploitation as sources of timber for construction or wood carving [54].

Usage Categories with High Numbers of Reports
The 134 medical reports of Fabaceae species in Zimbabwe (Tables 1 and 2) are classified into 19 major health disorder categories following the International Classification of Primary Care's classification system [19]. Most use records are in the categories of gastrointestinal problems (92 usage reports) and female reproductive problems (58 usage reports) (Table 2). Similarly, gastrointestinal problems, reproductive problems in women, respiratory problems and sexually transmitted infections (Table 2) are treated with the highest number of species. The categories of gastrointestinal problems, reproductive problems, respiratory problems and sexually transmitted infections are among the 10 major causes of death in Zimbabwe [55]. Muchandiona [56] argued that the prevalence of gastrointestinal disorders and respiratory infections is due to poor solid waste management by the local councils in Zimbabwe, which has worsened over the years. Similarly, gastrointestinal disorders, such as diarrhoea and dysentery, are also a major concern in neighbouring countries such as Mozambique [57][58][59] and South Africa [60][61][62]. Therefore, gastrointestinal problems are among the most common reasons local people use traditional medicines and consult traditional healers [57,[59][60][61][62].

Usage Categories with High Numbers of Reports
The 134 medical reports of Fabaceae species in Zimbabwe (Tables 1 and 2) are classified into 19 major health disorder categories following the International Classification of Primary Care's classification system [19]. Most use records are in the categories of gastrointestinal problems (92 usage reports) and female reproductive problems (58 usage reports) ( Table 2). Similarly, gastrointestinal problems, reproductive problems in women, respiratory problems and sexually transmitted infections (Table 2) are treated with the highest number of species. The categories of gastrointestinal problems, reproductive problems, respiratory problems and sexually transmitted infections are among the 10 major causes of death in Zimbabwe [55]. Muchandiona [56] argued that the prevalence of gastrointestinal disorders and respiratory infections is due to poor solid waste management by the local councils in Zimbabwe, which has worsened over the years. Similarly, gastrointestinal disorders, such as diarrhoea and dysentery, are also a major concern in neighbouring countries such as Mozambique [57][58][59] and South Africa [60][61][62]. Therefore, gastrointestinal problems are among the most common reasons local people use traditional medicines and consult traditional healers [57,[59][60][61][62]. Charms and ritual objects 15 26 Convulsions and epilepsy 9 18 Depressed fontanelle 12 24 Ethnoveterinary medicine 10 20 Table 2. Cont.

Phytochemistry and Pharmacological Properties of Fabaceae Species
The Fabaceae species used as sources of traditional medicines in Zimbabwe are rich in chemical constituents ( Table 3). The majority of these species are characterized by flavonoids (57.4%), followed by terpenoids (42.6%), tannins (40.6%), saponins (34.7%), phenolics (30.7%) and alkaloids (28.7%) ( Table 3). Research by Wink [78] showed that the main secondary metabolites of the Fabaceae family include alkaloids, non-protein amino acids, cyanogens, peptides, phenolics, polyketides and terpenoids. This author argued that these secondary metabolites serve as defence compounds against herbivores and microbes and also serve as signal compounds to attract pollinating and fruit-dispersing animals. Fabaceae species used as traditional medicines and food plants are characterized by nutrients such as proteins, lipids, carbohydrates, mineral elements, fatty acids, amino acids, fibres and vitamins, which are important for animal and human health [79,80]. The majority of documented species have several proven pharmacological activities (Table 3) such as inhibition of the acetylcholinesterase enzyme, and anticancer, antidiabetic, antifertility, anthelmintic, antiamoebic, anti-inflammatory, antimicrobial, antioxidant, antiparasitic, cytotoxic, hepatoprotective, hypoglycaemic and immunomodulatory effects. Despite the discovery of several secondary metabolites in the Fabaceae family, its species have attracted disproportionately little attention in the context of ethnopharmacological research over the years. The relative importance of the Fabaceae species as medicinal plants is demonstrated by the fact that about 10% of the species documented in this study are commercially important. The species that are commercially developed with potential to be developed into health products or pharmaceutical drugs and are regularly traded on the international markets include Abrus precatorius, Albizia adianthifolia, Cajanus cajan, Colophospermum mopane, Dichrostachys cinerea, Lessertia frutescens, Senna italica, Senna occidentalis, Tamarindus indica, Vachellia karroo and Vachellia nilotica [77,81].

Phytochemistry and Pharmacological Properties of Fabaceae Species
The Fabaceae species used as sources of traditional medicines in Zimbabwe are rich in chemical constituents ( Table 3). The majority of these species are characterized by flavonoids (57.4%), followed by terpenoids (42.6%), tannins (40.6%), saponins (34.7%), phenolics (30.7%) and alkaloids (28.7%) ( Table 3). Research by Wink [78] showed that the main secondary metabolites of the Fabaceae family include alkaloids, non-protein amino acids, cyanogens, peptides, phenolics, polyketides and terpenoids. This author argued that these secondary metabolites serve as defence compounds against herbivores and microbes and also serve as signal compounds to attract pollinating and fruit-dispersing animals. Fabaceae species used as traditional medicines and food plants are characterized by nutrients such as proteins, lipids, carbohydrates, mineral elements, fatty acids, amino acids, fibres and vitamins, which are important for animal and human health [79,80]. The majority of documented species have several proven pharmacological activities (Table 3) such as inhibition of the acetylcholinesterase enzyme, and anticancer, antidiabetic, antifertility, anthelmintic, antiamoebic, anti-inflammatory, antimicrobial, antioxidant, antiparasitic, cytotoxic, hepatoprotective, hypoglycaemic and immunomodulatory effects. Despite the discovery of several secondary metabolites in the Fabaceae family, its species have attracted disproportionately little attention in the context of ethnopharmacological research over the years. The relative importance of the Fabaceae species as medicinal plants is demonstrated by the fact that about 10% of the species documented in this study are commercially important. The species that are commercially developed with potential to be developed into health products or pharmaceutical drugs and are regularly traded on the international markets include Abrus precatorius, Albizia adianthifolia, Cajanus cajan, Colophospermum mopane, Dichrostachys cinerea, Lessertia frutescens, Senna italica, Senna occidentalis, Tamarindus indica, Vachellia karroo and Vachellia nilotica [77,81]. Table 3. Phytochemistry and pharmacological properties of Fabaceae species used as traditional medicines in Zimbabwe.

Species
Phytochemistry Pharmacological Activities References  Table 3. Phytochemistry and pharmacological properties of Fabaceae species used as traditional medicines in Zimbabwe.

Conclusions
This review is a compilation of literature sources on the Fabaceae species used as traditional medicines in Zimbabwe, providing an important repository of ethnopharmacological data required for future studies. The Fabaceae family is characterized by several species used as traditional medicines for the treatment and management of different ailments and diseases. The literature search showed that there is a paucity of information on the cultural practices associated with usage of Fabaceae species, including information on their dosages and administration. Therefore, there is a need for ethnobotanical research into and documentation of the cultural value of the Fabaceae species in Zimbabwe. Fabaceae species that are exotic to Zimbabwe are also used as sources of traditional medicines, corroborating the general observation that traditional pharmacopoeias are not static social institutions but fluid and dynamic, characterized by the addition of exotic plant species as herbal medicines.
Several Fabaceae species used as traditional medicines are known to contain bioactive compounds which have demonstrated diverse pharmacological properties against several disease-causing pathogens. Plant extracts and phytochemical compounds isolated from Fabaceae species have shown inhibition of the acetylcholinesterase enzyme and many other properties, such as antitumor, antidiabetic, antifertility, anthelmintic, antiamoebic, anti-inflammatory, antimicrobial, antioxidant, antiparasitic, cytotoxic, hepatoprotective, hypoglycaemic and immunomodulatory. However, the majority of the studied biological activities have mainly been in vitro assays, while clinical and in vivo studies are lacking. It is recommended that the unstudied biological activities of the medicinal species should be investigated to unravel the therapeutic potential of the considered Fabaceae species, using both in vitro and in vivo models. Furthermore, the toxicological properties of these species should be evaluated and the mechanism of action of the identified phytochemicals should be elucidated based on their pharmacological properties.

Conflicts of Interest:
The author declares no conflict of interest.