An Investigation into the Acute and Subacute Toxicity of Extracts of Cassipourea flanaganii Stem Bark In Vivo.

The conventional use of medicinal plants is in part based on the widespread belief that plant crude extracts are non-toxic. In South Africa, traditional preparations of Cassipourea flanaganii used to treat hypermelanosis have accordingly been regarded by many as non-toxic. Whether that is so impacts on the potential of bark extracts to be developed as a commercial drug to treathypermelanosis, given their documented capacity to inhibit tyrosinase activity. Our study investigated the acute and subacute toxicity of the methanol extract of C. flanaganii bark in rats. Wistar rats were randomly assigned into different treatment groups. The rats received a daily oral gavage of crude extract for acute and subacute toxicity tests. Haematological, biomechanical, clinical and histopathology examinations were carried out to evaluate the possible toxicity of C. flanaganii. The results were subjected to the Student's t-test and ANOVA. For both acute and subacute toxicity, there was no statistical difference between the groups. There were no clinical or behavioral signs of toxicity observed in the rats. No treatment-related gross pathology lesions and no histopathology were observed. The findings of this study demonstrate the absence of acute or subacute toxicity after oral treatment with C. flanaganii stem bark extracts in Wistar rats at the levels administered. Chemical profiling of the total extract using LC-MS tentatively identified eleven (11) compounds as the major chemical constituents.

The effect of isolates from Cassipourea flanaganii (Schinz) alston, a plant used as a skin lightning agent, on melanin production and tyrosinase inhibition.

ETHNOPHARMACOLOGICAL RELEVANCE: The Zulu and Xhosa people of South Africa use the stem bark of Cassipourea flanaganii as a skin-lightning cosmetic. AIM OF THE STUDY: To isolate and identify compounds responsible for the skin lightning properties from the stem bark of Cassipourea flanaganii and to evaluate their cytotoxicity towards skin cells. MATERIALS AND METHODS: Extracts from the stem bark of Cassipourea flanaganii were isolated using chromatographic methods and structures were determined using NMR, IR and MS analysis. The tyrosinase inhibitory activity and the ability to inhibit the production of melanin were determined using human primary epidermal melanocyte cells. Cytoxicity was established using the same melanocytes and a neutral red assay. RESULTS: One previously undescribed compound, ent-atis-16-en-19-al (1) along with the known ent-atis-16-en-19-oic acid (2), ent-atis-16-en-19-ol (3), ent-kaur-16-en-19-oic acid (4), ent-kaur-16-en-19-al (5), ent-manoyl oxide (6), guinesine A (7), guinesine B (8), guinesine C (9), lichenxanthone (10), 2,4-dihydroxy-3,6-dimethyl benzoic acid methyl ester (11), lynoside (12), lupeol (13), ß-amyrin (14), docosyl ferulate (15), stigmasterol, sitosterol and sitosterol-O-glucoside were isolated in this investigation. An impure fraction containing compound 3 was acetylated to obtain 19-acetoxy-ent-atis-16-ene (3a). Compounds 10 and 11 are usually isolated from lichen, hence they are possible contaminants of lichen harvested with the bark. Compounds 1, 3a, 5-14 were not significantly cytotoxic to the primary epidermal melanocyte cells (P > 0.05) when compared to the negative and positive controls (DMSO, 0.1% and hydrogen peroxide, 30 wt% in water). Inhibition of tyrosinase was significantly greater with respect to the negative control (P < 0.001) for compounds 3a, 5-8 and 9-10 at 10 µM and for compounds 5-8 and 9-10 at 100 µM. Compared to hydroquinone (the positive control) at 10 µM, the level of inhibition was comparable or to that of compounds 3a, 5, 6, and 8-10 at 10 µM, with 9 and 10 showing a greater level of inhibition. Inhibition of melanin was both concentration and time dependent for all compounds tested with higher melanin content at 24 h compared to 48 h s and at 10 mM compared to100 mM at both time points; melanin content was significantly lower for hydroquinone at both time points and concentrations. CONCLUSIONS: Compounds 1, 5-14, isolated from Cassipourea flanaganii and the derivative 3a showed low cytotoxicity. All compounds had a clear time and concentration dependent effect on melanin content which did not appear to be dependent on their inhibition of tyrosinase.

Constituents of Bulbs of three Species of the Hyacinthaceae (Hyacinthoideae): Eucomis vandermerwei, E. zambesiaca and Resnova humifusa.

Phytochemical analyses of the bulbs of Eucomis vandermerwei and E. zambesiaca yielded homoisoflavonoids and triterpenoid derivatives. A new (17S*23S*)-epoxy-3ß,15ß,29-trihydroxy-27-norlanost-8-en-24-one) was isolated from E. zambesiaca. Resnova humifusa yielded homoisoflavonoids, and a tetrahydropyran derivative, 2-methyl-3-(4S*,5R *,7S*-trihydroxy-8S*-hydroxymethyltetrahydro-6H-4-pyranyl)-2-propenoic acid. All compounds were assayed for COX-2 inhibition of cyclooxygenase; 3,5,7-trihydroxy-3-(4'-methoxybenzyl)-4-chromanone was found to have significant activity.

Isoflavones from Calpurnia Aurea subsp. aurea and their anticancer activity.

BACKGROUND: Calpurnia aurea is an African medicinal plant used in many countries in Africa to treat a range of medical conditions or disorders. Extracts of the plant were shown to be active in antibacterial and antioxidant assays as well as against lice, ticks and maggots. The aim of the study was to isolate the phytochemical constituents from the plant and to test them in appropriate bioassays dependent on the compounds isolated in order to provide a rationale for the use of the plant in ethno-medicine or to provide some information on its constituents. MATERIALS AND METHODS: The stem and bark of the plant was extracted with organic solvents of varying polarity and the extracts separated and purified using column chromatography. The isolated compounds were identified by NMR spectroscopy and the compounds were tested for their in vitro anticancer activity against breast (MCF7), renal (TK10) and melanoma (UACC62) human cell lines using an in house method developed at the CSIR, South Africa. RESULTS: The isoflavones, 4',5,7-trihydroxyisoflavone (1), 7,3'-dihydroxy-5'-methoxyisoflavone (2), 7-hydroxy-4',8-dimethoxyisoflavone (3), 7-acetoxy-4',8-dimethoxyisoflavone (4) and 3',7-dihydroxy-4',8-dimethoxyisoflavone (5), a pterocarpan (3-acetoxy-9-methoxypterocarpan) and a quinolizidine alkaloid (calpurnine) were isolated from the stem and bark of Calpurnia aurea. The tetrasubstituted isoflavone 5 was found to be the most active in the three cell lines amongst all the compounds tested. This was followed by trisubstituted isoflavone 2. CONCLUSION: The isoflavones showed moderate activity against the renal, melanoma and breast cancer cell lines tested against, with the isoflavones 2 and 5 showing the best activity of the compounds tested. These isoflavones may have a synergistic effect with other anticancer drugs.

Use of circular dichroism to determine the absolute configuration of a pimarane diterpenoid from the southern African Sclerocroton integerrimus (Euphorbiaceae).

From the stem bark and leaves of Sclerocroton integerrimus, eight compounds, including 17-hydroxy-ent-pimara-8(14),15-dien-3-one (1), were isolated. The structures of the compounds were determined on the basis of spectroscopic analysis. The absolute configuration of 17-hydroxy-ent-pimara-8(14),15-dien-3-one was confirmed from electronic circular dichroism studies.

COX-2 inhibitory activity of homoisoflavanones and xanthones from the bulbs of the Southern African Ledebouria socialis and Ledebouria ovatifolia (Hyacinthaceae: Hyacinthoideae).

The bulbs of Ledebouria socialis (Hyacinthaceae) yielded the benzocyclobutene homoisoflavonoid, (R)-2',5-dihydroxy-3',4',7-trimethoxyspiro{2H-1-benzopyran-3-(4H)-9-bicyclo[4.2.0]octa[1,3,5]triene}-4-one, socialinone (1). Ledebouria ovatifolia yielded (2ε,3R)-2,5-dihydroxy-7-methoxyspiro[2H-1-benzopyran-3(4H), 5'(6'H)-cyclobuta[f][1,3]benzodioxol]-4-one (2) and the homoisoflavanone, (E)-3-(3',4'-dihydroxybenzylidene)-5,7-dihydroxychroman-4-one, ovatifolionone (5), the dihydrochalcone, 4,4'-dihydroxy-2',6'-dimethoxydihydrochalcone (3), and xanthone, 1,6-dihydroxy-2,3,5-trimethoxy-8-methyl-9H-xanthen-9-one (4) along with 21 known compounds. Structures were determined using spectroscopic techniques. The anti-inflammatory activities of the homoisoflavonoids and xanthones isolated were evaluated against cyclooxygenase-1 and -2 isoenzymes. (R)-3-(3',4'-Dihydroxybenzyl)-7-hydroxy-5-methoxychroman-4-one (7), (E)-3-(3',4'-dihydroxybenzylidene)-7-hydroxy-5-methoxychroman-4-one (10), 1,3,6-trihydroxy-2-methoxy-8-methylxanthen-9-one (6) and ovatifolionone acetate (5Ac) exhibited significant activity against cyclooxygenase-2 at <10µM.

The chemistry and biological activity of the Hyacinthaceae.

The Hyacinthaceae (sensu APGII), with approximately 900 species in about 70 genera, can be divided into three main subfamilies, the Hyacinthoideae, the Urgineoideae and the Ornithogaloideae, with a small fourth subfamily the Oziroëoideae, restricted to South America. The plants included in this family have long been used in traditional medicine for a wide range of medicinal applications. This, together with some significant toxicity to livestock has led to the chemical composition of many of the species being investigated. The compounds found are, for the most part, subfamily-restricted, with homoisoflavanones and spirocyclic nortriterpenoids characterising the Hyacinthoideae, bufadienolides characterising the Urgineoideae, and cardenolides and steroidal glycosides characterising the Ornithogaloideae. The phytochemical profiles of 38 genera of the Hyacinthaceae will be discussed as well as any biological activity associated with both crude extracts and compounds isolated. The Hyacinthaceae of southern Africa were last reviewed in 2000 (T. S. Pohl, N. R. Crouch and D. A. Mulholland, Curr. Org. Chem., 2000, 4, 1287-1324; ref. 1); the current contribution considers the family at a global level.

Non-toxic melanin production inhibitors from Garcinia livingstonei (Clusiaceae).

ETHNOPHARMACOLOGICAL RELEVANCE: The stem bark of Garcinia livingstonei is used traditionally as a skin lightening agent. AIM OF THE STUDY: To isolate and identify compounds responsible for the observed skin lightening activity of Garcinia livingstonei and to evaluate their cytotoxicity. MATERIALS AND METHODS: Constituents of the stem bark and fruits of Garcinia livingstonei were isolated using chromatographic techniques and structures were determined using 1D and 2D NMR and MS analysis. MeWo cells were used to evaluate the cytotoxicity and impact on melanin levels of extracts and compounds isolated, in vitro. RESULTS: Twelve known compounds, morelloflavone (1), morelloflavone-7″-sulphate (2), guttiferone A (3), sargaol (4), isojacareubin (5), 6-deoxyisojacareubin (6) and in addition to the common triterpenoids, betulin, betulin aldehyde, lupeol, lupenone, euphol and stigmasterol were isolated in this investigation. Morelloflavone, morelloflavone-7″-sulphate and sargaol, were found to be considerably less cytotoxic and more effective as skin lightening agents than hydroquinone. CONCLUSIONS: A range of compounds was isolated from the stem bark and fruit of Garcinia livingstonei. Although the bark extract contained the cytotoxic guttiferone A, it was found to be less toxic than hydroquinone, and morelloflavone, the 7″-sulphate derivative and sargaol show potential for development as depigmentation/skin lightening agents.

Screening of selected ethnomedicinal plants from South Africa for larvicidal activity against the mosquito Anopheles arabiensis.

BACKGROUND: This study was initiated to establish whether any South African ethnomedicinal plants (indigenous or exotic), that have been reported to be used traditionally to repel or kill mosquitoes, exhibit effective mosquito larvicidal properties. METHODS: Extracts of a selection of plant taxa sourced in South Africa were tested for larvicidal properties in an applicable assay. Thirty 3rd instar Anopheles arabiensis larvae were exposed to various extract types (dichloromethane, dichloromethane/methanol) (1:1), methanol and purified water) of each species investigated. Mortality was evaluated relative to the positive control Temephos (Mostop; Agrivo), an effective emulsifiable concentrate larvicide. RESULTS: Preliminary screening of crude extracts revealed substantial variation in toxicity with 24 of the 381 samples displaying 100% larval mortality within the seven day exposure period. Four of the high activity plants were selected and subjected to bioassay guided fractionation. The results of the testing of the fractions generated identified one fraction of the plant, Toddalia asiatica as being very potent against the An. arabiensis larvae. CONCLUSION: The present study has successfully identified a plant with superior larvicidal activity at both the crude and semi pure fractions generated through bio-assay guided fractionation. These results have initiated further research into isolating the active compound and developing a malaria vector control tool.

Quinolizidine alkaloids from Sophora velutina subsp. zimbabweensis (Fabaceae: Sophoreae).

Three novel quinolizidine alkaloids, N-methylenehydroxycytisine (1), 6,7-dihydroxylupanine (2), and velutinine (3) have been isolated from the fruits and pods (1 and 2) and stem bark (3) of Sophora velutina subsp. zimbabweensis along with the known quinolizidine alkaloids, 7-hydroxylupanine (4), thermopsine (5), N-methylcytisine (6), cytisine (7), an aromatic ester, methyl-3-(3',4'-dimethoxyphenyl)-2-propenoate (8) and the triterpenoids, lup-20(29)-ene-3beta-ol (9) and 12-oleanen-3-one (10). Compounds 6 and 10 showed good antibacterial activity against E. faecalis, with MIC values of 20.8 and 10.9 microg mL(-1), respectively. The other compounds tested exhibited low to moderate antibacterial activity.

Toddaculin, a natural coumarin from Toddalia asiatica, induces differentiation and apoptosis in U-937 leukemic cells.

Chemotherapeutics represent the main approach for the treatment of leukemia. However, the occurrence of adverse side effects and the complete lack of effectiveness in some cases make it necessary to develop new drugs. As part of our screening program to evaluate the potential chemotherapeutic effect of natural coumarins, we investigated the anti-leukemic activities of a series of six prenylated coumarins isolated from the stem bark of Toddalia asiatica (Rutaceae). Among these, 6-(3-methyl-2-butenyl)-5,7-dimethoxycoumarin (toddaculin) displayed the most potent cytotoxic and anti-proliferative effects in U-937 cells. To determine whether these effects resulted from induction of cell death or differentiation, we further evaluated the expression of several apoptosis and maturation markers. Interestingly, while toddaculin at 250 µM was able to induce apoptosis in U-937 cells, involving decreased phosphorylation levels of ERK and Akt, 50 µM toddaculin exerted differentiating effects, inducing both the capacity of U-937 cells to reduce NBT and the expression of differentiation markers CD88 and CD11b, but no change in p-Akt or p-ERK levels. Taken together, these findings indicate that toddaculin displays a dual effect as a cell differentiating agent and apoptosis inducer in U-937 cells, suggesting it may serve as a pharmacological prototype for the development of novel anti-leukemic agents.

In vitro anti-plasmodial activity of Dicoma anomala subsp. gerrardii (Asteraceae): identification of its main active constituent, structure-activity relationship studies and gene expression profiling.

BACKGROUND: Anti-malarial drug resistance threatens to undermine efforts to eliminate this deadly disease. The resulting omnipresent requirement for drugs with novel modes of action prompted a national consortium initiative to discover new anti-plasmodial agents from South African medicinal plants. One of the plants selected for investigation was Dicoma anomala subsp. gerrardii, based on its ethnomedicinal profile. METHODS: Standard phytochemical analysis techniques, including solvent-solvent extraction, thin-layer- and column chromatography, were used to isolate the main active constituent of Dicoma anomala subsp. gerrardii. The crystallized pure compound was identified using nuclear magnetic resonance spectroscopy, mass spectrometry and X-ray crystallography. The compound was tested in vitro on Plasmodium falciparum cultures using the parasite lactate dehydrogenase (pLDH) assay and was found to have anti-malarial activity. To determine the functional groups responsible for the activity, a small collection of synthetic analogues was generated - the aim being to vary features proposed as likely to be related to the anti-malarial activity and to quantify the effect of the modifications in vitro using the pLDH assay. The effects of the pure compound on the P. falciparum transcriptome were subsequently investigated by treating ring-stage parasites (alongside untreated controls), followed by oligonucleotide microarray- and data analysis. RESULTS: The main active constituent was identified as dehydrobrachylaenolide, a eudesmanolide-type sesquiterpene lactone. The compound demonstrated an in vitro IC50 of 1.865 µM against a chloroquine-sensitive strain (D10) of P. falciparum. Synthetic analogues of the compound confirmed an absolute requirement that the α-methylene lactone be present in the eudesmanolide before significant anti-malarial activity was observed. This feature is absent in the artemisinins and suggests a different mode of action. Microarray data analysis identified 572 unique genes that were differentially expressed as a result of the treatment and gene ontology analysis identified various biological processes and molecular functions that were significantly affected. Comparison of the dehydrobrachylaenolide treatment transcriptional dataset with a published artesunate (also a sesquiterpene lactone) dataset revealed little overlap. These results strengthen the notion that the isolated compound and the artemisinins have differentiated modes of action. CONCLUSIONS: The novel mode of action of dehydrobrachylaenolide, detected during these studies, will play an ongoing role in advancing anti-plasmodial drug discovery efforts.

Screening for adulticidal bioactivity of South African plants against Anopheles arabiensis.

BACKGROUND: This study was conducted to evaluate whether a selection of South African ethnomedicinal plants included in this study displayed insecticidal properties when screened against adult stages of the mosquito. METHODS: 381 crude extracts of 80 plant taxa in 42 families were sprayed onto ceramic tiles and screened using the cone bio-assay method for insecticide efficacy testing. Blood-fed, female Anopheles arabiensis mosquitoes were exposed to the treated tiles for a period of sixty minutes. Mosquito mortality was monitored for twenty-four hours. RESULTS: Of all the extracts analysed, the highest activity was observed in Ptaeroxylon obliquum (Ptaeroxylaceae) and Pittosporum viridiflorum (Pittosporaceae), a single extract from each, exhibiting more than 50% mortality. A large proportion (81.63%) of the extracts tested displayed low levels of mosquitocidal activity. The remainder of the extracts (17.85%) exhibited no bioactivity (0% mortality). CONCLUSIONS: The screening results have shown that in accordance with WHO standards, none of the crude extracts tested had exhibited greater than 60% mortality against the adult stages of the malaria vector Anopheles arabiensis.

Triterpenoid acids and lactones from the leaves of Fadogia tetraquetra var. tetraquetra (Rubiaceae).

Four triterpenoids isolated from the leaves of Fadogia tetraquetra var. tetraquetra, 3beta-hydroxy-11alpha, 12alpha-epoxyoleanan-28,13beta-olide (1), 3beta-hydroxyurs-11-en-28,13beta-olide (2), oleanolic acid (3), and ursolic acid (4), were evaluated for their antiviral and antibacterial properties. Compound 4 showed potent activity against the Semliki Forest virus with an IC50 of 14.7 microM, but was also found to be significantly cytotoxic (68% reduction in cell viability after 24 hours exposure at 50 microM) towards baby hamster kidney (BHK21) host cells. A viability assay on the mammalian human hepatocellular carcinoma (Huh-7) cell line showed no significant effects on intracellular ATP content after 48 hours exposure to compounds 1-4 at this concentration. Compound 4 also inhibited Staphylococcus aureus (MIC 12.5 microM), but was inactive against Enterobacter aerogenes, Escherichia coli, and Pseudomonas aeruginosa. Compounds 1-3 were inactive against all tested bacterial strains at 50 microM concentration.

Evaluation of selected South African ethnomedicinal plants as mosquito repellents against the Anopheles arabiensis mosquito in a rodent model.

BACKGROUND: This study was initiated to establish whether any South African ethnomedicinal plants (indigenous or exotic), that have been reported to be used traditionally to repel or kill mosquitoes, exhibit effective mosquito repellent properties. METHODS: Extracts of a selection of South African taxa were tested for repellency properties in an applicable mosquito feeding-probing assay using unfed female Anopheles arabiensis. RESULTS: Although a water extract of the roots of Chenopodium opulifolium was found to be 97% as effective as DEET after 2 mins, time lag studies revealed a substantial reduction in efficacy (to 30%) within two hours. CONCLUSIONS: None of the plant extracts investigated exhibited residual repellencies >60% after three hours.

Cembranolides from the stem bark of the southern African medicinal plant, Croton gratissimus (Euphorbiaceae).

The stem bark of Croton gratissimus (Euphorbiaceae) yielded four cembranolides, including the first reported example of a 2,12-cyclocembranolide, (+)-[1R*,2S*,7S*,8S*,12R*]-7,8-epoxy-2,12-cyclocembra-3E,10Z-dien-20,10-olide, whose structure was confirmed by means of single crystal X-ray analysis. This compound showed moderate activity against the PEO1 and PEO1TaxR ovarian cancer cell lines.

Antidiabetic screening and scoring of 11 plants traditionally used in South Africa.

AIM: To investigate the traditional antidiabetic uses of indigenous or naturalised South African plants using an optimised screening and scoring method. MATERIALS AND METHODS: Eleven plant species were screened against Chang liver, 3T3-L1 adipose and C2C12 muscle cells measuring glucose utilisation in all three cell lines and toxicity in the hepatocytes and adipocytes only. A scoring system was devised to aid interpretation of results. RESULTS: Catharanthus roseus results correlated with previously reported in vivo results, with best stimulation of glucose utilisation in hepatocytes. Momordica foetida and Momordica balsamina extracts were active in myocytes but only the latter stimulated glucose utilisation in hepatocytes. Brachylaena discolor gave the best overall results, with all plant parts giving high activity scores and negligible toxicity. In vitro toxicity results for Catharanthus roseus, Vinca major, Momordica balsamina and some Sclerocarya birrea extracts raise concern for chronic use. CONCLUSION: This screening system increases the likelihood of identifying drug candidates using in vitro antidiabetic screening of crude plant extracts, whilst the scoring system aids data interpretation. ETHNOPHARMACOLOGICAL RELEVANCE: The multitude of metabolic steps affected by Type II diabetes offer many drug targets but they complicate in vitro screening to validate traditional uses or find new drug leads from plants.

Vascular myorelaxing activity of isolates from South African Hyacinthaceae partly mediated by activation of soluble guanylyl cyclase in rat aortic ring preparations.

The vasorelaxing effect of isolates (compounds 1, 2, 3, and 4 (homoisoflavanones), compound 5 (sesquiterpenoid), compounds 6 and 7 (bufadienolides)) from the South African Hyacinthaceae has been assessed using rat aortic ring preparations. Compounds 2, 3, and 4 inhibited the tonic contraction induced by both 60 mM K(+) (K60) and phenylephrine, compound 3 being the most potent. Compounds 5, 6, and 7 caused a modest concentration-dependent relaxation, whereas compound 1 was ineffective. Under K25- or K60-induced depolarization, compound 3 displayed antispasmodic effects not reversed by tetraethylammonium. Under precontraction induced with phenylephrine, compound 3 shifted to the left the concentration-relaxation curves of either isoprenaline or sodium nitroprusside. 1 H-[1,2,4] oxidazolol [4,3-a] quinoxalin-1-one shifted to the right the concentration-relaxation curve of compound 3, while 3'-isobutyl-1-methylxanthine had no effect. In the absence of extracellular Ca(2+), compound 3 (estimated pIC50 = 4.66) and ryanodine reduced the response to phenylephrine. Phenylephrine-stimulated influx of extracellular Ca(2+) was markedly reduced when tissues were pretreated with compound 3 (pIC50 = 5.14) or nifedipine, but stimulated by ryanodine. Compound 3 partially antagonized the contraction induced by phorbol 12-myristate-13-acetate. To our knowledge, this has been the first account describing the vasodilating activity of homoisoflavonoids: compound 3 proved an effective vasorelaxing agent, partly acting via the activation of soluble guanylyl cyclase.

Xanthones from Drimiopsis maculata.

Six new xanthones, drimiopsins A-F (1-6), have been isolated from the South African Drimiopsis maculata. The structures of these compounds were difficult to elucidate due to the lack of correlating protons seen in the NMR spectra, and INADEQUATE spectra were used to confirm the structures. Xanthones have not previously been reported from the Hyacinthaceae.

In vitro antiplasmodial activity of medicinal plants native to or naturalised in South Africa.

The increasing prevalence and distribution of malaria has been attributed to a number of factors, one of them being the emergence and spread of drug resistant parasites. Efforts are now being directed towards the discovery and development of new chemically diverse antimalarial agents. The present study reports on the in vitro antiplasmodial activity of 134 plant taxa native to or naturalised in South Africa, representing 54 families, which were selected semi-quantitatively using weighted criteria. The plant extracts were tested for in vitro activity against a Plasmodium falciparum strain D10 using the parasite lactate dehydrogenase (pLDH) assay. Of the 134 species assayed, 49% showed promising antiplasmodial activity (IC(50)< or = 10 microg/ml), while 17% were found to be highly active (IC(50)< or = 5 microg/ml). Several plant species and genera were shown for the first time to possess in vitro antiplasmodial activity. These results support a rational rather than random approach to the selection of antiplasmodial screening candidates, and identify a number of promising taxa for further investigation as plant-based antimalarial agents.