B.-E. Van Wyk

A broad review of commercially important southern African medicinal plants

AIMS OF THE STUDY Commercially important indigenous medicinal plants of southern Africa are reviewed in the context of fundamental knowledge about their ethnobotany, phylogeny, genetics, taxonomy, biochemistry, chemical variation, reproductive biology and horticulture. The aim is to explore the rapidly increasing number of scientific publications and to investigate the need for further research. MATERIALS AND METHODS The Scopus (Elsevier) reference system was used to investigate trends in the number of scientific publications and patents in 38 medicinal plant species. Fifteen species of special commercial interest were chosen for more detailed reviews: Agathosma betulina, Aloe ferox, Artemisia afra, Aspalathus linearis, Cyclopia genistoides, Harpagophytum procumbens, Hoodia gordonii, Hypoxis hemerocallidea, Lippia javanica, Mesembryanthemum tortuosum, Pelargonium sidoides, Siphonochilus aethiopicus, Sutherlandia frutescens, Warburgia salutaris and Xysmalobium undulatum. RESULTS In recent years there has been an upsurge in research and development of new medicinal products and new medicinal crops, as is shown by a rapid increase in the number of scientific publications and patents. Despite the fact that an estimated 10% of the plant species of the world is found in southern Africa, only a few have been fully commercialized and basic scientific information is often not available. CONCLUSIONS The limited available information indicates that some of the plants display remarkable regional variation in morphological, genetic and chemical characters that should be more thoroughly investigated. Basic biological information is needed to guide the rapidly accelerating commercialization process, especially the selection of superior clones, the development of new cultivars and the standardization of raw materials.

A review of Khoi-San and Cape Dutch medical ethnobotany

UNLABELLED ETHNOPHARMACOLOGICAL CONTEXT: Cape herbal medicine as a distinct and unique healing system is conceptualized for the first time, together with a first compilation of the authentic materia medica of the system. MATERIALS AND METHODS The early literature on Khoikhoi (Hottentot), San (Bushman) and Cape Dutch medicinal plants and medical practices is reviewed, with a focus on the Cape Floristic Region (from Namaqualand to the Eastern Cape). To avoid recent additions and modern cultural influences in the results, the date of publication of the last volume of Marloths Flora of South Africa (1932) was chosen as a cut-off date. RESULTS The recorded Cape materia medica (up to 1932) is briefly summarized, giving the scientific names, vernacular names (in Afrikaans or Khoi-San/Nama) and main uses. It comprises about 170 items and includes mainly indigenous and endemic plant species, some exotic (garden) plants, and a few other items (fungi, seaweeds, lichens, hyraceum and natural potassium nitrate). Most of the plants (and hyraceum) are still widely used today, especially in rural areas. CONCLUSIONS The combination of unique cultural practices and a diverse, highly endemic flora has led to the development of a distinct herbal healing system, here called Cape herbal medicine, but hitherto rather vaguely and inaccurately referred to as Khoi-San medicine, Cape Dutch medicine or boererate (farm remedies). The data allows for a more informed consideration of indigenous knowledge and intellectual property rights associated with particular plants (e.g. Hoodia and Pelargonium). It also offers opportunities for linking modern ethnobotanical field studies with historical data.

Fire-survival strategy — a character of taxonomic, ecological and evolutionary importance in fynbos legumes

Variation in the fire-survival strategy of the fynbos, legume tribesPodalyrieae andLiparieae was studied, since it is often the only conspicuous difference between morphologically similar taxa. Two main strategies are apparent: sprouters, taxa which are able to sprout from a woody rootstock after fire and non-sprouters, those which only recruit from seed after fire. In fynbos legumes sprouting and non-sprouting taxa differ in their habitat specificity, population densities, relative regional abundance, and in seed germination tempo. Speciation patterns, as inferred from an analysis of the geographical distribution and habitat specificity of the species, are discussed. Problems relating to the use of sprouting versus non-sprouting as a taxonomic character in fynbos legumes are addressed and possible solutions are given.

Recent advances in understanding Apiales and a revised classification

Despite the long history of recognising the angiosperm order Apiales as a natural alliance, the circumscription of the order and the relationships among its constituent groups have been troublesome. Recent studies, however, have made great progress in understanding phylo- genetic relationships in Apiales. Although much of this recent work has been based on molecular data, the results are congruent with other sources of data, including morphology and geography. A unified picture of relationships has now emerged regarding the delimitation of Apiales, which includes a core group of four families (Apiaceae, Araliaceae, Myodocarpaceae, Pittosporaceae) to which three small families are also added (Griseliniaceae, Torricelliaceae and Pennantiaceae). After a brief review of recent advances in each of the major groups, a revised classification of the order is presented, which includes the recognition of the new suborder Apiineae (comprising the four core families) and two new subfamilies within Apiaceae (Azorelloideae and Mackinlayoideae).

A review of ethnobotanical research in southern Africa

The diversity of plant species in southern Africa is matched by an equally rich cultural diversity, but traditional uses of plants have not yet been systematically recorded. Available information is fragmentary and widely dispersed in many different journals and books. A survey by Liengme (1983a) has shown several gaps in the scientific literature and some progress has been made towards a more complete record of indigenous plant use in the region. Information on some ethnic groups, such as the Khoi, Ndebele and Swazi, as well as the interaction between plants and people, folk taxonomies, plant-related mythology, ethnoveterinary medicine and pre-colonial plant use are some of the aspects that still remain poorly recorded. In contrast, ethnopharmacology — particularly the testing of biological activity of crude extracts and isolated compounds — has received considerable attention in recent years. The aim of these studies is usually to validate traditional uses rather than to provide information for product development. A review of the literature on various categories of plant use, including recent publications and some hitherto unpublished research, is presented. Ethnobotany remains an underdeveloped discipline in southern Africa and there is an urgent need to systematically document indigenous knowledge on traditional plant use before it becomes irretrievably lost to future generations.

Phenolic variation in wild populations of Aspalathus linearis (rooibos tea)

Abstract Rooibos tea, a herbal tea derived from Aspalathus linearis (Fabaceae—tribe Crotalarieae) has become increasingly popular as a health drink. The beneficial properties are partly ascribed to the phenolic constituents in the plant, which are enzymatically modified during processing. Within the species, distinct geographical forms can be recognised, differing in habit, fire-survival strategy, vegetative and reproductive morphology, enzyme patterns and flavonoids. Several phenolic compounds are known to occur in A. linearis . The main constituent of the commercial tea type (also known as the Rocklands type or the red tea type) is the dihydrochalcone aspalathin, but the presence of other flavonoids such as nothofagin, orientin, isoorientin, vitexin, rutin and isoquercetrin has been reported. These compounds are found in the processed product, as well as the dried leaves. The relative quantities of phenolic compounds show large qualitative and quantitative differences between populations and provenances of the wild tea types. Within populations, however, the patterns are remarkably uniform. Aspalathin was found to be the main compound in processed (“fermented”) tea and also in dried leaves of several tea types. The compound is absent in some wild tea populations, where other flavonoids occur as the main phenolics, notably orientin, isoorientin and rutin. Rutin is invariably the main compound in Aspalathus pendula , a close relative of A. linearis that is rarely used to make tea. An overview of natural variation in phenolic compounds of the main wild tea types is presented.

Circumscription of Apiaceae tribe Oenantheae

Previous molecular systematic investigations into the higher-level relationships of Apiaceae subfamily Apioideae have revealed a strongly supported clade recognised as tribe Oenantheae Dumort. These plants may have clusters of fibrous or tuberous-thickened roots, corky-thickened fruits, and other adaptations for existence in wet or aquatic habitats. In some species, the leaves may be finely dissected or linear-septate and much reduced. We have initiated collaborative studies to produce a comprehensive estimate of phylogeny of the tribe, but such investigations are thwarted because information on the composition of the tribe is lacking. Herein, tribe Oenantheae is circumscribed to include the following genera: Afrocarum, Berula, Bifora (pro parte), Cicuta, Cryptotaenia (pro parte), Cynosciadium, Daucosma, Helosciadium, Lilaeopsis, Limnosciadium, Neogoezia, Oenanthe, Oxypolis, Perideridia, Ptilimnium, Sium, and Trepocarpus. Relationships inferred from phylogenetic analyses of nuclear rDNA ITS sequences from 64 accessions representing all 17 genera reveal that four genera are not monophyletic. Bifora and Cryptotaenia have members that fall outside of the tribe; Berula and Sium each comprise two or more lineages within Oenantheae. The St Helena endemics, Sium bracteatum and S. burchellii, ally with African Berula erecta; this clade is sister to the African endemic species Sium repandum and Afrocarum imbricatum, and this entire group is allied closely with north temperate Berula erecta. Nomenclatural changes are in order, but must await further study. Representatives of eight genera native to North America comprise a monophyletic group, and results from relative rate tests suggest that this lineage is evolving much faster than any other major clade recognised within the tribe.

Distribution and chemotaxonomic significance of flavonoids inAloe (Asphodelaceae)

A chemotaxonomic study of practically all the species of the genusAloe showed that flavonoids occur as major compounds in 31 out of a total of 380 species investigated. Flavanones and dihydroflavonols are present in the exudate of species inAloe ser.Rhodacanthae andSuperpositae and also in a number of the endemic species from Madagascar. Flavones occur as the only major compound in the leaf extracts of the sects.Leptoaloe andGraminialoe. In ser.Macrifoliae and inLomatophyllum, the sister genus ofAloe, isovitexin co-occurred with theC-glucosylanthrone aloin. The chemotaxonomic implication of these results are discussed together with the significance of the taxonomic and chemogeographical distribution of flavonoids inAloe. With a few rare exceptions, the leaf compounds from two different biogenetic pathways (polyketide pathway and flavonoid pathway) are mutually exclusive. Since flavonoids are restricted to the basal groups inAloe, we conclude that flavonoids are plesiomorphic characters inAloe reflecting ancient phylogenetic and biogeographic links.

Generic relationships in Araliaceae: looking into the crystal ball

Our understanding of relationships among Apiales and within Araliaceae has progressed considerably in the last decade thanks to numerous molecular phylogenetic studies. It is now clear that traditional infrafamilial systems of classification of Araliaceae fail to reflect evolutionary relationships and that the morphological features on which they were based exhibit high levels of homoplasy. Recent studies have provided a very different picture of relationships in the family, and are rapidly converging on a consensus that allows us to review the status of the 41 genera currently recognised in Araliaceae and to consider alternative circumscriptions for those that are not monophyletic. Twenty-four small and medium-sized genera are unlikely to be modified, whereas five others ( Dendropanax , Oreopanax , Osmoxylon , Pseudopanax and Sinopanax ) may require changes in circumscription. The status of four other small genera is not yet clear, but the two largest genera will require considerable re-alignments: Polyscias (c. 150 spp.), which is paraphyletic with respect to six other genera, and the polyphyletic genus Schefflera (c. 650-900 spp.), which represents five geographically distinct clades. While it is still too early to make formal taxonomic changes to these genera, current evidence suggests that Polyscias sensu lato will likely be realigned into 5–8 geographically coherent genera, while Schefflera sensu lato will be split into 10–16 genera.

Growth inhibition of plant pathogenic bacteria and fungi by extracts from selected South African plant species

Extracts from 26 plant species representing 16 families, collected in the Free State Province of South Africa, were tested in vitro for their potential to inhibit the growth of eight plant pathogenic fungi and five plant pathogenic bacteria. None of the crude extracts showed any mycelial growth inhibition of the eight test fungi. All of the extracts inhibited the growth of one or more of the five plant pathogenic test bacteria, but to varying degrees. Crude extracts from Acacia karroo and Elephantorrhiza elephantina inhibited the growth of four bacteria, while that of Euclea crispa, Acacia erioloba, Senna italica and Buddleja saligna inhibited the growth of all five plant pathogenic bacteria. Of these, the crude extract of Euclea crispa was clearly superior to the rest as it compared more favourably to that of a commercial bactericide, Dimethyl Dodecyl Ammonium Chloride (DDAC). Subsequently, the Euclea crispa crude extract was fractionated by means of liquid-liquid extraction using four organic solvents, hexane, diethyl ether, chloroform and ethyl acetate, in order of increasing polarity. This was done in an attempt to assess the antimicrobial potential of the more concentrated fractions. Once again, none of the semi-purified fractions showed any antifungal activity. However, antibacterial activity was located in the more polar ethyl acetate fraction indicating that the substances involved were very similar in polarity and/or structure. From this it seems justified to further purify the ethyl acetate fraction of the Euclea crispa extract and attempt to identify the active substance(s) involved.