The Status of Bark in South African Traditional Health Care

Minireview

The status of bark in South African traditional health care

OM Grace1, HDV Prendergast2, J van Staden1* and AK Jäger1

1 Research Centre for Plant Growth and Development, School of Botany and Zoology, University of Natal Pietermaritzburg, Private Bag X01 Scottsville 3209, South Africa 2 Centre for Economic Botany, Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3AE, United Kingdom * Corresponding author, email: [email protected]

Received 22 October 2001, accepted in revised form 2 November 2001

Bark products constitute nearly one third of plant mate- agement and plant part substitution are discussed. rial used in South African traditional medicine. Since the Effective implementation of these action plans is reliant large majority of South Africans make use of traditional on the dissemination of existing and new knowledge. health care, bark is fundamental to the traditional phar- The prevailing scenario of a non-sustainable bark sup- macopoeia. In this review we consider the status of bark ply has impacted negatively on the quality of bark prod- resources, as reflected by the literature, and highlight ucts available to the consumer, as problems of incorrect the need for multi-disciplinary research to address the identification and purposeful adulteration arise. To facil- lack of available information on plant species used for itate monitoring and standardisation, phytochemical their bark. The supply of bark to the medicinal plant references should be established for bark authentica- trade has been rendered non-sustainable, due to tion, and used in conjunction with morphological and increased user populations and reduced indigenous anatomical characters for identification in the case of vegetation. Whilst conservation of the South African unknown specimens. The importance of bark in South flora is paramount, natural resources cannot meet the African traditional health care warrants attention from current, nor foreseeable, demand for bark. Alternatives all research sectors to conserve the country’s rich floral such as tree propagation and cultivation, strategic man- heritage, and the integrity of traditional health care.

Introduction

African traditional health care has become the subject of and sale. Plants are, therefore, either killed or limited to increasing research momentum over recent decades. asexual reproduction by harvesting. In contrast, leaves are Traditional health care systems throughout the continent the most commonly used plant part in other regions of Africa share characteristics such as the extent to which traditional (Cunningham 1990), harvesting of which is less likely to medicine is used (80% of the population in developing coun- affect plant vigour and reproductive capacity. tries being the definitive statistic of the World Health Problems of resource sustainability have strongly influ- Organisation (WHO) (Penso 1980)), importance in the deliv- enced supply and demand in the traditional medicine trade. ery of primary health care, and growing recognition of this This medicinal plant trade represents a vast ‘hidden econo- medical pluralism, where patients may choose between bio- my’ (Cunningham 1988), with an estimated annual value in medical and traditional health care (Gesler 1984, Dauskardt 1998 of R270 million per annum (US$3 million) (Mander 1990). Cultural parallels include spiritual principles and treat- 1998) and has likely appreciated considerably since then. ment methodologies employed by traditional healers (Iwu Bark is the most popular product in South Africa harvested 1993, Srivastava et al. 1996). from trees, and comprises in volume at least 27% of the Southern African systems of traditional health care differ market produce traded annually in KwaZulu-Natal (Mander significantly from those of other regions of the continent in 1998). Since the medicinal plant trade in South Africa and the plant material used. In South Africa, the trade in tradi- neighbouring countries is centred in KwaZulu-Natal tional medicine plants is dominated by material with a long (Cunningham 1988, Mander et al. 1996, Marshall 1998, shelf life: bark, roots, bulbs, whole plants, seeds and fruits Williams et al. 2000), this is further indicative of the national (Cunningham 1990). Storability of plant material is impor- trade (up to R1.35 million or US$1.5 million in 1998 (Mander tant, as a lengthy time period may lapse between harvesting 1998)) in bark products. 22 Grace, Prendergast, Van Staden, Jäger

Trees comprise 65% of all medicinal plants used world- affecting a database currently being compiled to document wide; 8 000 of them are globally threatened (Gates 2000). the use and properties of barks used in traditional medicine The South African flora is well known for its richness and in KwaZulu-Natal, sourced primarily from the literature. An diversity of species: the 21 377 recorded species constitute indication of the sparse information available, even for ten of approximately 10% of the world’s plant diversity, of which the most popular plant species used for their bark in this 10% are threatened (Goldring 1999). Estimates of the South province, is shown in Table 1. Despite concerns voiced for African traditional pharmacopoeia range between 700 the South African flora threatened by medicinal exploitation, (Mander 1998) and 3 000 higher plant species (Van Wyk et there is a lack of comprehensive information to empower al. 1997). Some 130 medicinal species, at least 112 of which efforts of conservation, trade monitoring and health care are harvested for their bark, come from indigenous forest, standardisation. This needs to be addressed — a problem which now covers only 0.3% of South Africa (Cooper 1985, with resolution in increasing South African ethnobotanical Mander et al. 1997, Cunningham 1988). research and publications in recent years (see Cunningham The impact of traditional health care on the South African (2001a) for a review of African ethnographic literature and flora is unlikely to abate soon. Current trends indicate that Hedberg (1993) for a discussion of botanical methods in the expected increase in the demand for traditional medi- ethnographic research). Literature dealing with other cines in South Africa is indeed occurring. Factors influencing aspects of bark research, such as anatomy and phytochem- the demand for traditional medicinal plants include popula- istry, are prolific, but historically fraught with confusion in ter- tion growth, slow employment rate, influx of foreigners seek- minology (for discussions, see Martin and Crist 1970, Borger ing work, and limited government resources for welfare 1973, Trockenbrodt 1990 and Junikka 1994). Furthermore, upliftment (Mander et al. 1996). More recently, the AIDS phytochemical and pharmacological investigations of medic- pandemic and international demands for medicinal plant inal barks have focussed on traditional American and Asian products have also been identified (Mander 1998). The healthcare. simultaneous effects of rising consumer demands and declining plant resources threaten the integrity of traditional The effects of bark harvesting health care in South Africa. This review focuses on the use of bark in South African The supply of traditional medicine products from forests in traditional medicine as reflected by the literature. We high- South Africa has been affected by exploitation for timber by light the importance of medicinal bark products, and there- European settlers since the eighteenth century. Afforestation fore the urgent need to address the sustainability of avail- and forest clearance for agriculture similarly reduced indige- able resources, which in turn influences the quality of bark- nous forest and savannah vegetation (see, for example, derived medicines. Authentication is a key aspect to the Palmer and Pitman 1961, Cooper 1985, Cooper and Swart monitoring of this situation, and we briefly discuss methods 1992). King (1941 cited in Cunningham 1988) reported that and problems of authenticating bark. Multi-disciplinary by 1901, exploitable timber — including many species used research is needed to deal with the complex issues sur- for traditional medicine — was exhausted from 52% of rounding the use of bark in South African traditional health forests in the Transkei region. Today, indigenous forest in care. some regions of KwaZulu-Natal has been reduced by up to 90% (Cunningham 1988). According to Mander (1998), the Problems with the literature potential area of forests exploitable for medicinal harvesting in the province has deteriorated from 889km2 to 260km2. Despite the importance of bark in South African traditional Most indigenous forest in KwaZulu-Natal remains privately medicine, ethnobotanical literature about it is scant or inac- owned, thereby at risk of similar irreversible exploitation due cessible. There are several accounts of traditional plant to landowners’ ignorance of management practice (Cooper medicines in South Africa (e.g. Watt and Breyer-Brandwijk 1985). The grassland, savannah and thicket biomes in the 1962, Cunningham 1988, Roberts 1990, Hutchings et al. province have been reduced by 60% (Mander 1998). 1996, Van Wyk et al. 1997, Van Wyk and Gericke 2000 and Reduction in harvestable vegetation which were formerly Williams et al. 2000 and 2001). Several publications on the actual or potential sources of medicinal plants has increased South African flora have included medicinal usage (Palmer the use of remaining areas (Cunningham 1988). and Pitman 1961, Immelman et al. 1973, Coates Palgrave The supply of tree products is not a problem intrinsic to 1977, Pooley 1993, Mander et al. 1995, Scott-Shaw 1999). traditional health care. Prior to the commercialisation of tra- Ethnobotanical accounts of the South African flora, such as ditional medicine, a variety of traditional management prac- those of Gerstner in 1938 and 1939 (cited in George et al. tices secured sustainability of tree resources. Throughout 2001), Watt and Breyer-Brandwijk in 1962, and Bryant in Africa, trees are conserved for their shade and edible fruits, 1966 (cited in George et al. 2001), succeeded in document- and — indirectly — medicinal products (Cunningham 1990). ing early ethnographic information before it disappeared Protection of vegetation (natural or cultivated) at burial sites (George et al. 2001). However, none address barks in paris common, and many beliefs and taboos associated with ticular. Where barks are explicitly mentioned, the value of plant collection may be interpreted as conservation meas- data is frequently reduced by vague information: omitting to ures (Cunningham 1990, Van Wyk et al. 1997). For example, detail user populations, localities, correct botanical nomen- bark used in therapy of renal ailments is sometimes only clature, sources of plant material, or methods of medicinal harvested from the eastern and western sides of the tree, preparation. These were found to be the limiting factors symbolic of the kidneys, thereby preventing ringbarking (Van South African Journal of Botany 2002, 68: 21–30 23

Table 1: Trade and conservation of ten popular bark species in KwaZulu-Natal, South Africa

Species Biome1 Conservation status in Harvesting response Urban wholesale Annual trade KwaZulu-Natal price (R) volume Ocotea bullata Forest Declining and vulnerable to Will coppice and R2.89/kg2; 25.3 tonnes2 (Burch.) Baill. extinction3; protected4 recoppice vigorously3, but R20–R25/bag*3 (LAURACEAE) not after heavy damage6 Warburgia salutaris Forest, Endangered, protected4,5 May show complete R4.44/kg2; 17.2 tonnes2 (Bertol. f.) Chiov. Grassland regrowth after ringbarking, R120/bag*3 (CANNELACEAE) and vigorous coppice3 Prolific root suckers develop in response to mild root damage7 Curtisia dentata (Burm. f.) Forest Vulnerable and declining3; Produces vigorous R2.22/kg2; 23.9 tonnes2 Chiov. (CORNACEAE) conservation-dependant coppice3 R30/bag*3 and protected4 Sclerocarya birrea (A. Rich.) Grassland Not threatened No data No data No data Hochst. (ANACARDIACEAE) Acacia xanthophloea Benth. Grassland Not threatened No data R10/bag*3 153 bags*3 (FABACEAE – MIMOSACEAE) Albizia adianthifolia Forest Declining3 No data No data No data (Schumach.) W. Wight (FABACEAE – MIMOSACEAE) Harpephyllum caffrum Bernh. Forest Not threatened Produces coppice and No data 424 bags*3 ex Krauss (ANACARDIACEAE) will recoppice Cassine papillosa (Hochst.) Forest Declining3 No data No data 146 bags*3 Kuntze (CELASTRACEAE) Cassine transvaalensis Grassland Declining3 No data R15/bag*3 No data (Burtt Davy) Codd (CELASTRACEAE) Rapanea melanophloeos (L.) Forest Not threatened No data R10/bag*3 327 bags*3 Mez (MYRSINACEAE)

1 Sensu Low and Rebelo (1998); 2 Mander (1998); 3 Cunningham (1988); 4 Scott-Shaw (1999); 5 Hilton-Taylor (1996); 6 Creig (1984); 7 Mander et al. (1995) * Bags refer to standard 50kg-size maize bags. While no estimates of the mass of bark material contained in one bag are provided, Cunningham (1988) estimated that one bag may represent the bark of three Ocotea bullata trees with diameters of 40–44cm at breast height

Wyk et al. 1997). Purposeful conservation measures are tra- high diversity but low species density, to maximise their ditionally implemented by community leaders and enforced income. Extensive species-selective exploitation has a by community headmen and policemen (Cunningham marked effect on forest structure, as the rate of canopy gap 1990). An illustration of this is the prohibition of hunting, cut- formation exceeds that caused by natural disturbance ting of saplings for construction, and the collection of fuel- (Cunningham 1988). Bark harvesting is typically concentrat- wood in Dwesa and Manubi forests (Transkei region, South ed in sites accessible by vehicle; La Cock and Briers (1992) Africa) imposed on the Gcaleka tribe by their chief to con- noted that in Tootabie Nature Reserve (Eastern Cape serve such resources (Cooper and Swart 1992). According Province, South Africa) bark harvesting was not evident in to Cunningham (2001b) habitat or resource conservation is sites adjacent to a parking area in which extensive harvest- implemented when three criteria are met: the subject is val- ing had already occurred. However, continued harvesting ued, human impact threatens this value, and social or politi- pressure on the site was expected to induce harvesting in cal conservation controls are enforceable. less accessible areas of the reserve. Management strate- Conservation efforts in communities and areas protected gies to prevent uncontrolled bark harvesting in this case by legislation are now frequently disregarded because of the included the fencing-off of concealed parking areas at the lucrative demand for commercial harvesting (Cunningham site, regular patrolling, and monitoring of further harvesting. 1990). Despite its protected status, the popular bark species Preventative measures against bark harvesting are increas- Warburgia salutaris (Bertol. f.) Chiov. is extremely rare in ingly drastic: bark removal may be effectively discouraged KwaZulu-Natal, and extinct even within the boundaries of by barbed wire wrapped around the tree trunk, or the bark protected areas such as Hluhluwe Game Reserve (Mander painted with a dilute emulsion of water-based coloured PVC et al. 1996). Use of natural resources will, in many regions paint. This practice renders the bark unusable for medicinal of southern Africa, take place irrespective of whether it is its purposes, apparently without affecting tree vigour (Creig permissible or not (Dzerefos 1999). Commercial gatherers 1984). Ironically, graffiti have also shown to protect trees either select forests with a high density of a few species, or against bark harvesters (Creig 1984). 24 Grace, Prendergast, Van Staden, Jäger

The removal of bark may kill trees by effectively interrupt- latex producing Ficus species, such as Ficus natalensis ing downward phloem translocation. In response, carbohy- Hochst. (Moraceae), are able to withstand complete bark drate photosynthetic products and growth hormones diffuse removal (Cunningham and Mbenkum 1993). Examples of from the phloem above the wound to the xylem, and enter post harvest management of trees to promote bark regrowth the upward transpiration stream, causing a concentration of include the wrapping of the trunk of Ficus natalensis with these compounds in the aerial parts (Kozlowski and Pallardy banana leaves in Uganda (pers. comm. Dominic Byarugaba 1997). The efficacy of bark removal as a management prac- to Prendergast 1999) and a similar application with plastic tice to manipulate flowering and fruiting in economic crops is for Eucommia sp. (Eucommiaceae) in China (pers. comm. well documented in the literature (for example, partial ring- Bengang Zhang to Prendergast 2000). Bark production may barking of fruit trees induces early fruiting and reduces also occur on new shoots. Cinchona spp. (Rubiaceae), cul- vigour). However, the extent and season in which bark tivated for their quinine-containing bark since the mid-nine- removal is conducted may result in overall loss of vigour or teenth century, are felled for complete bark removal and death of the tree. Excessive depth and width of bark removal allowed to coppice. The reactions of many plants to inter- results in slow callus formation in the wound, depletion of vention — such as bark removal and felling — may be carbohydrates in the roots, and eventual root injury and species-specific or widely applicable, but knowledge about death (Kozlowski and Pallardy 1997). them may be largely scattered in horticultural literature or Although bark may be harvested without killing the tree, among the wealth of unwritten indigenous knowledge. death is usually the outcome of the volume and frequency of Continual bark removal will cause death even where cop- bark removal for the traditional medicine trade. Bark is pice production is prolific, as plants are debarked when removed using an axe or cane knife (machete), and is usu- immature (Cunningham 1988); subsequent prevention of ally dried prior to being transported to markets and shops seed set adversely affects population structure. Of urgent (Mander 1998). According to Cunningham (1988) and importance, therefore, in the conservation of tree species Cunningham and Mbenkum (1993), serious bark damage used for bark products (and indeed for other economic pur- constitutes removal of ≥10% of the trunk bark below head poses, such as fuelwood and timber) is knowledge of their height. Extensive bark removal (usually resulting in ring- ability to withstand harvesting pressure, and of their regen- barking) is the most common harvesting technique used by eration responses (see Table 1 for the paucity of information commercial gatherers, and the stripping of smaller pieces of about ten popular bark species in KwaZulu-Natal). Such bark where trees are repeatedly required for low-volume information would assist in the selection of appropriate man- harvests (Cunningham 1990). Thick bark from the main agement practices for individual trees, and natural or culti- trunk of mature trees is preferred (Mander 1998). Initially, vated populations. the trunk is stripped to a maximum height of 3m, but when bark is scarce, ladders are built to access bark in the crown Alternatives to harvesting from the wild of the tree and branches are felled (Cunningham 1988). Wastage is tremendous if the tree is killed by bark stripping The demand for forest products cannot be met by the con- on the trunk, before bark on the upper portion of the tree is servation of natural resources alone, and alternatives to har- utilised (Cunningham 1988). Cunningham (1991) noted that vesting them are needed. Sustainable supply of grassland, in the case of Warburgia salutaris bark is harvested even savannah and thicket tree species (e.g. Acacia spp., Albizia when partially regrown, until both aerial parts and roots are adianthifolia (Schumch.) W. Wight, Cussonia spicata entirely debarked. Thunb.) may be achieved through intensive management, Non-sustainable harvesting for the traditional medicine as relatively large populations will remain on grazing land of trade in South Africa, and indeed throughout the continent, commercial livestock farms in the future (Mander 1998). has the highest impact on popular, slow-growing and slow However, cultivation of forest species is necessary in order reproducing species with specific habitat requirements and a to alleviate harvesting pressure and sustain biodiversity in limited distribution (Cunningham 1990). Many tree species the remaining forest fragments in this country (Mander used for their bark qualify as such. Peters (1994) noted that 1998). The need to cultivate popular indigenous plants was management potential of bark as a non-timber forest prod- identified by Gerstner nearly 60 years ago (Mander et al. uct (NTFP) is significantly lower than products such as fruits, 1996), and highlighted thereafter by a number of workers seeds, exudates and leaves. (see, for example, Cunningham 1988, 1990, Williams 1996, Coppicing ability and the vulnerability of trees to the and Jäger and Van Staden 2000). Since then, commercial effects of bark removal are important attributes that vary with cultivation of indigenous trees has been largely neglected the physiology (Cunningham 1991), ecology and taxonomy due to a lack of farmers’ understanding of marketing and cul- of different species, which may facilitate effective manage- tivation economics, although cultivation trials have shown ment for continual bark harvesting. Some indigenous trees good potential for meeting consumer demands, and lessen- used for traditional medicine products are extremely sensi- ing the effects of the trade on biodiversity (Mander et al. tive to bark removal (for example Faurea macnaughtonii 1996). Phill. (Proteaceae) and Podocarpus henkelii Stapf. ex. The use of cultivated plants in traditional medicine not only Dallim. & Jacks (Podacarpaceae)), while others such as alleviates pressure on natural populations, but facilitates Warburgia salutaris and Nuxia floribunda (Benth.) may show standardisation and increased safety, as inconsistencies in complete regrowth after ringbarking (Cunningham 1991). the quality and composition (due to genotypic and pheno- Prunus africana (Hook. f.) Kalkm. (Rosaceae), and some typic variation) are reduced, probabilities of misidentification South African Journal of Botany 2002, 68: 21–30 25 and adulteration are lowered, and yields raised by manage- indigenous forest in order to optimise opportunities in mar- ment practice (WHO, IUCN and WWF 1993). In accordance ket supply. Bark may be a potential by-product from the tim- with guidelines laid out by WHO, IUCN and WWF (1993), ber industry in the Cape Province, where indigenous forests cultivation allows simultaneous ex situ conservation of are exploited for high-value timber (Mander 1998). Similarly, medicinal plant species and in situ conservation of natural land clearance for development or agricultural purposes populations in their natural habitats. Mander et al. (1996) may also provide a source of barks, albeit irregular reported that Mondi, a South African timber company, mass- (Cunningham 1988). There is therefore great potential for produced popular medicinal trees. Warburgia salutaris and lasting bark supplies as a consequence of management Catha edulis (Vahl) Forssk. ex Endl. are propagated in practice aimed at sustaining other products from trees, such KwaZulu-Natal by the Medicinal Flora Co-Operative, which as timber and fuelwood. Shackleton (2000) noted that endeavours to propagate certain South African medicinal knowledge of management of coppice dynamics of indige- plants for existing markets (Anon 2000). (Contentious issues nous trees might help to increase regrowth rates and/or the surrounding the role of horticultural propagation in ex situ number of coppice shoots for fuelwood. Thus, sustained medicinal plant conservation are discussed by Crouch availability of both fuelwood and medicinal bark may be (2000)). An important consideration, however, is phytochem- simultaneously achieved. ical variation within plant populations, between cultivated Another solution to the problem of meeting demands for and naturally occurring specimens, and chemotypes within medicinal plant material without compromising natural pop- taxa. Dahlgren and Van Wyk (1988), for example, noted that ulations is the practice of plant part substitution. Non-sus- the sweet scent emitted by Greyia sutherlandii Hook. ex tainable products such as bark, bulbs and roots may be Harv. (Greyiaceae) at certain times of the year was not replaced with aerial parts such as leaves and twigs, as har- detectable in cultivated specimens. Standardisation of vesting of these parts inflict less damage (Zschocke et al. herbal medicines in terms of plant material, properties and 2000b). It is well known that phytochemical constituents are usage has been dealt with thoroughly in the literature (see sometimes alike in different organs of a plant species, and George et al. 2001, McChesney 2001, Fabricant and therefore show similar biological activity. For example, phy- Farnsworth 2001). tochemical constituents of the bark and leaves of Ocotea It is unlikely that even commercial forests of indigenous bullata (Burch.) Baill. are very similar, and exhibit similar bio- trees would be able to meet the short-term demand for bark logical activity in vitro (Zschocke et al. 2000a), as is the case products in KwaZulu-Natal, but cultivation would ensure for Warburgia salutaris bark and leaves (Zschocke et al. supply in the long-term (Mander 1998). Slow growing 2000b). In KwaZulu-Natal, some healers are managing cul- species that are unlikely to be cultivated by commercial tivated Ocotea bullata and Warburgia salutaris saplings for enterprises will need to be the focus of government and coppice production, thereby inducing high leaf yields that NGO (Non-Governmental Organisation) activities, and are used instead of bark (pers. comm. Steve McKean to would require extensive rotational area to ensure availability Grace 2001). In many cases, however, certain plant parts (Cunningham 1990, Mander 1998). Tree plantations are are chosen and used for very particular reasons — not unattractive to farmers with limited resources, as the matu- always phytochemical — and may not be substitutable. ration period is non-productive, although long-term product Whilst sustainable harvesting may be possible, deviation yields may be lucrative. Propagation of medicinal trees is from such management practice to increase yields and largely considered a secondary crop to enhance income- income is a real threat in any system. For example, generating potential of land used for cash crops and mono- Cunningham and Mbenkum (1993) reported over-harvesting culture. Research and educational programmes, aiming to of Prunus africana bark in Cameroon for European export increase cultivation of medicinal plants as cash crops, are (bark extract is a patented ingredient in pharmaceuticals to concentrated on rapid income-generating herbaceous and treat prostatic hyperplasia). Bark is sourced exclusively from shrubby plants (Jäger and Van Staden 2000). It is clear that natural populations, and while the species is particularly government, NGOs and parastatals may be the only poten- resilient to bark removal, excessive harvesting pressure has tial source of bark medicines in the near future, at least until impacted strongly on existing populations. Pressures on the forestry for NTFPs is viewed as a commercially viable farm- need for sustainable resources to secure both biodiversity ing option. Commercialisation of other NTFPs is rising as and the livelihoods that depend on these resources are developers seek new commercial opportunities, and devel- debated by Van Staden (1999). opment agencies seek to improve the welfare of rural communities (Shackleton 2001). Although exploitation of NTFPs Products, therapy and trade may intensify the problem of unsustainable tree resources, commercialisation under the auspices of carefully managed Bark medicines are used in treatments for a diversity of ail- projects may indeed secure sustainability. An example of the ments, spanning all levels of healthcare, from first aid to pre- latter is the ‘Marula Commercialisation for Sustainable ventative and rehabilitative therapy, and for magical or reli- Livelihoods Project’, funded by the UK Department for gious purposes. Trends in usage and preparations are not International Development (DfID), which focuses on com- apparent in the literature. The popularity of barks, attributa- mercialisation of NTFPs from Sclerocarya birrea in southern ble to their medicinal efficacy, may be justified by typically Africa (Shackleton 2001). high concentrations of active constituents (Van Wyk et al. In the interim, Mander (1998) recommended the demand 1997). Bark may have been favoured historically, as it is for bark products might be co-ordinated with logging in readily accessible and availability unaffected by seasons, 26 Grace, Prendergast, Van Staden, Jäger whereas the leaves, flowers and fruits of trees may not be. bark products by the untrained is a growing problem (pers. Bark products are sold either as partially processed chunks comm. Elliot Ndlovu to Grace 2001). (10–30cm x 3–10cm), or processed into chopped and Yet another factor affecting patient safety, as plant ground products (<1mm) (Mander 1998), that are some- resources become scarce, is the quality of plant medicines. times sold in mixtures of various plant ingredients. A crudely Barks used in traditional medicines may vary in quality and fashioned mortar and pestle, usually made from thick iron efficacy with age of harvested material (immature bark may piping, is used to grind the material (Mander 1998). The not contain the same concentrations of secondary metabo- healer or trader subsequently prepares raw products, usual- lites), shelf life, rates of degradation and time since harvest. ly alone and less commonly with other ingredients, for fur- Determination of bark shelf life is made difficult because the ther preparation and self-administration by the patient. rhytidome (usually a large portion of bark used) is already Methods of preparation generally aim to facilitate extraction dead prior to harvesting, and the time since death on the of active principles — the ‘power of force’ — from the plant tree cannot be determined. Mander et al. (1997) found that material (Kokwaro 1995). Accordingly, bark is commonly traditional healers continue to employ certain plant parts, powdered and extracted prior to use. Liquid preparations despite reduced maturity and size of material, as the use of such as decoctions and infusions, administered orally or by other plant parts of the same species is in many cases unac- enema, are used most frequently for internal complaints. For ceptable. the treatment of external ailments, such as injuries and der- The motivation to market medicinal plants is frequently not matological ailments, powdered bark or ointments are used. to provide an essential service, but financial gain (Manana More specialised methods of administration include the and Eloff 2001). Whilst highly trained practitioners of tradi- application of powdered bark to incisions made by the traditional medicine are reliable sources of therapy and medi- tional healer, and the burning of bark to treat spiritual and cines, traders are seldom qualified (Cunningham 1988), and psychological complaints. there is an increasing abundance of healers without qualifi- cation or training at all (Cunningham 1988, Bye and Dutton Impacts on the quality of bark medicines 1991, Ngubane 1992). Consumers are reliant upon the per- son from whom medicine is purchased to correctly identify Cunningham (1990) noted that the species-specific demand plant medicines, but under current circumstances where the for traditional plant medicines means that alternatives are seller may not be dependable, patient safety is jeopardised. not easily provided due to the plants’ particular characteris- Stewart and Steenkamp (2000) noted that misidentification, tics, their symbolism, or the form in which they are taken. faulty preparation and inappropriate dosage (particularly in However, indigenous medicine — like any profession — is paediatric cases) are the principal causes of poisonings evolving as the supply and demand dynamic changes related to the use of traditional plant medicines. (Mander 1998). Formerly common products are now includ- The margin of error in identifying plant material is ed only in more expensive ‘special’ mixes. For example, the increased with other characteristics of traditional medicine. bark of Curtisia dentata (Burm. f.) C. A. Sm. (Cornaceae) is Synonymy in vernacular names is characteristic of many tra- found only in ‘special ikhabulo’, whereas it was once includ- ditional plant medicines. For example, Sideroxylon inerme ed in ‘ordinary’ mixes (Cunningham 1988). Alternative prod- L., Mimusops caffra E. Mey. ex A.DC. and Mimusops obo- ucts are available at lower prices, for example the bark of the vata Sond. (Sapotaceae) share the Zulu name amasethole, exotic Calamus L. sp. (Palmae) is used instead of Warburgia but their barks, although morphologically alike, are used for salutaris (Cunningham 1988). Although costs may influence different purposes (Cunningham 1988, Hutchings et al. the use of an alternative species, market prices are general- 1996). ly inelastic and wholesale prices remain significantly lower than retail prices (Mander 1998). Therefore cost alone can- Authentication of bark products used in traditional not be considered a predictor for substitution; availability of health care rare material from wholesalers is also likely to influence substitution or adulteration of bark products. Because medicinal bark products are sold in pieces and in Similar species or ‘mock-ups’ are substituted for scarce powdered form, identification is extremely difficult. Yet bark ingredients in the case of mythical plants: the bark of Ocotea can be very useful for tree identification in the field, as it is bullata is replaced with that of Cryptocarya latifolia Sond. usually typical at least at the genus level, and sometimes the and C. myrtifolia Stapf. (Lauraceae), as they share a similar species level (Acacia xanthophloea Benth. is easily identifi- odour, and Mondia whitei (Hook. f.) Skeels (Periplocaceae) able by the exceptional yellow-green, powdery bark). Bark roots are substituted with the exotic Cinnamomum zeylan- morphology, odour, flavour, characteristics of a slash wound icum (Burch.) Baill. (Lauraceae) (Cunningham 1988). made in the bark, and exudates, may provide reliable infor- Perhaps the most obvious example of changes in traditional mation in field identification of trees to the generic or specif- medicines is the availability of patent remedies and pharma- ic level (see Beard 1944, Wood 1952, Whitmore 1961, Tait ceutical medicines at traditional medicine stores, where and Cunningham 1988, Prance and Prance 1993, plant remedies for common complaints are no longer readi- Cunningham 2001b). However, field characters are of limit- ly available (Cunningham 1988). Although examples of the ed value for identification and authentication of excised bark change in composition of bark products have not been doc- products due to their usually ephemeral nature, and umented recently, traditional medical practitioners increas- because they are sometimes obvious to experts only. Tait ingly make use of generic bark products, and adulteration of and Cunningham’s (1988) report for the identification of South African Journal of Botany 2002, 68: 21–30 27 common medicinal plant products represents the single be necessary in the characterisation of herbal drugs available key for South African medicinal barks, using mor- (Gibbons and Gray 1998, Jork et al. 1990). Qualitative phological characters such as odour, flavour, colour, texture, assessment is perhaps more useful in the case of bark and presence or absence of oxalate crystals. extracts, due to the variability of tissue and possibility of dis- Bark anatomy is widely dismissed as too variable to be crepancies in quantitative data (Srivastava 1964). reliable for taxonomic purposes. However, in some cases Diagnostic phytochemical TLC fingerprints have been anatomical studies have yielded useful trends to augment found to correspond with existing taxonomic trends, or indi- taxonomy. Whitmore (1961) identified seven distinct bark cate alternative relationships, in plant genera such as types in 103 species of Malaysian Dipterocarpaceae, and Combretum (Combretaceae) (Carr and Rogers 1987) and reported that subjective field characters were converted to Maytenus (Celastraceae) (Rogers et al. 2000). Drewes et al. objective features with analyses of bark tissues. Similarly, (1998) reported chemical similarities, identified by prepara- bark surface patterns were correlated with internal structure, tive chromatography and spectroscopy, in the barks of and two bark types identified, in 12 southern African species Loxostylis alata Spreng. f. Reichb. and Smodingium argutum of the genus Eugenia (Myrtaceae) (Van Wyk 1985). E. Meyer ex Sonder, two members of the Anacardiaceae. Bark anatomy has traditionally offered the primary means Quality control of herbal medicines is an important topic for identification and authentication of bark products. Today, wherever they are used (Manana and Eloff 2001). most plant drugs included in pharmacopoeia are identifiable Standardisation and authentication of traditional South by chemical standards (Trease and Evans 1983), but African plant medicines are not well documented, although microscopy remains an important tool in the authentication the South African Traditional Medicines Research Group or identification of plant materials, especially for powdered (SATMERG) is compiling monographs for a pharmacopoeia drug mixtures (Jackson and Snowdon 1990). Successful of herbal medicines for this country. Some South African identification or authentication is reliant on recognition of plant species used in traditional medicine were investigated microscopical diagnostic cell types and ergastic contents for diagnostic anatomical characters and wound healing (Trease and Evans 1983). According to Trease and Evans effects by Adams et al. (2001). Manana and Eloff (2001) (1983), plant drug characterisation should aim to determine reported that phytochemical fingerprints of material sold in tissue and cell size, cell shape and relative positions, and markets in Pretoria compared closely to fingerprints of refer- the chemical nature of cell walls and cell contents. ence material, an encouraging result in the context of this Diagnostic characters of unprocessed and powdered bark discussion. samples are determinable by morphological and anatomical With problems of adulteration and substitution, there is a analysis. Further characterisation with various chemical and growing need for low-cost, repeatable and reliable tech- physical tests, such as histological staining, ash analyses, niques to identify bark specimens used in traditional South and fluorescence behaviour, are commonly employed in African medicine. Due to the practical difficulties of working investigations of bark pharmacognosy (Jolly 1966, Sanyal with bark tissue, the use of phytochemical fingerprints in the and Datta 1981, 1986). Srivastava (1964) cautioned that first instance certainly meets these requirements. However, chemical analyses of cell wall components and ergastic con- the variability of bark tissue calls for additional considera- tents should be used only within the context of thorough tion; Srivastava (1964) stressed the need for assessment of anatomical studies of processed and unprocessed bark seasonal variations in ergastic contents. The value of samples. anatomical and morphological bark characters, to augment Chemotaxonomic characters, many of which are definitive chemical methods of identification and address variability, for a taxon, may be of greater significance than morpholog- should be upheld. ical characters for plant identification (Trease and Evans 1983), and chemical analyses (notably chromatography) are Points of action now accepted as standard techniques for the identification of plant materials (Jackson and Snowdon 1990). In addition to Given the extent to which traditional health care is used in morphological and anatomical characters, chemical data are South Africa, the importance of medicinal bark products is important indicators of plant relationships at a different level apparent. Under difficult circumstances, where neither of structural organisation (Rogers et al. 2000). Reliable health care nor the indigenous flora of our country should be chemical characters are those that are exclusive to special- compromised, the need for sustainable bark resources is ist groups; ubiquitous primary compounds and those typical urgent. Debates of ex situ and in situ conservation need to of higher taxonomic levels have little value in separating taxa be clarified, and species-specific management practices (for a review of bark phytochemistry, see Srivastava 1964). established to ensure that these efforts succeed. To secure The use of Thin Layer Chromatography (TLC) to demon- the quality and efficacy of bark medicines, phytochemical strate the most characteristic constituents of a plant extract references must be established, against which medicinal or preparation is favoured for its simplicity, rapidity, and bark products may be authenticated, and the variability of affordability (Gibbons and Gray 1998). The resultant chro- bark products investigated. The diminished resources in matogram may be interpreted via qualitative (visual) assess- South Africa, and slow recovery rate of indigenous forests in ment, or semi-quantitative analysis of constituents shown particular, require that bark research receive a share of the (Rios et al. 1985, Wagner and Bladt 1995). However, expanding ethnobotanical field in this country. because plant extracts are usually complex mixtures of dif- Acknowledgements — The National Research Foundation is ferent compounds, other chromatographic techniques may thanked for financial support. 28 Grace, Prendergast, Van Staden, Jäger

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