Pelargonium sidoides DC. (Synonym: Pelargonium sidaefolium (Thunb.) R. Knuth; Common names: Umckaloabo, Uvendle, Kalwerbossie, Khoaara e nyenyane; Family: Geraniaceae) is a perennial geophyte predominantly found in the Eastern Cape Province of South Africa and the Lesotho highlands. The plant is adapted to a wide altitudinal range, spanning from near sea level in the Eastern Cape to 2746 m in the Lesotho highlands (Newton et al., 2013) . The plant is widely used by local communities as a traditional medicine for curing various ailments, including diarrhoea, colic, gastritis, tuberculosis, cough, hepatic disorders, menstrual complaints and gonorrhoea (Brendler and van Wyk, 2008; Colling et al., 2010) . The roots are also the main ingredient in a remedy used to treat a stomach ailment known as instila in infants (Hutchings et al., 1996) . Powdered plant materials which are soaked in water are used as a facial cream in the treatment of skin pimples (Lewu et al., 2007) . This indicates that Pelargonium sidoides may exhibit antibacterial properties. Probably the most compelling ethnobotanical use of Pelargonium sidoides has been in the treatment of tuberculosis, which subsequently led to its introduction in Europe in the late 1890s (Bladt and Wagner, 2007; Brendler and van Wyk, 2008) . The traditional ethno-veterinary applications of Pelargonium sidoides include the use of root decoctions as an anthelmintic remedy in calves (Hutchings et al., 1996) ; boiled leaves to protect wounds against maggots; and the prevention of purging in horses (Brendler and van Wyk, 2008 ). An extract obtained by soaking the roots in water is administered orally in the treatment of dysentery in cattle (Lewu et al., 2007) . Based on its medicinal properties in the treatment of respiratoryrelated ailments, Pelargonium sidoides has been formulated into phytopharmaceuticals, namely EPs s 7630 (Umckaloabo s , Dr. Willmar Schwabe GmbH & Co. KG Pharmaceuticals, Germany) and Linctagon s (Nativa, South Africa). The commercial success of Umckaloabo s is attributed to numerous factors, including 4 15 years of extensive scientific and clinical research (Gericke, 2011) . On the other hand, only negligible research (Bourdette, 2012; Motsamai, 2012) has been done to evaluate the efficacy and safety of Linctagon s (which mainly contains 350 mg Pelargonium sidoides, 500 mg Vitamin C, 50 mg bromelain, 80 mg quercetin, 5 mg zinc). This review provides a synthesis of the state of scientific knowledge on the pharmacology and safety evaluation of Pelargonium sidoides as well as exploring the potential of plant biotechnology applications in its conservation.
The extensive use of Pelargonium sidoides in traditional medicine coupled with its popularisation in modern medical systems in Europe have led to an upsurge in scientific exploration of its chemical composition in an effort to identify the active principles. This has resulted in a considerable body of literature exploring the phytochemical properties of Pelargonium sidoides (Gödecke et al., 2003 (Gödecke et al., , 2005 Hauer et al., 2010; Kayser and Kolodziej, 1995; Latté et al., 2000; Schoetz et al., 2008) . Details of the phytochemistry of the plant were comprehensively summarised in an excellent review by Kolodziej (2007) . However, identification of individual chemical constituents responsible for specific pharmacological activities has remained largely elusive. The chemical constituents of the root ethanolic extract of the plant consist largely of oligo-and polymeric proanthocyanidins, which are based on gallocatechin and epigallocatechin moieties (Theisen and Muller, 2012) . The pharmacological efficacy of Pelargonium sidoides has been partly attributed to the biological activity of highly oxygenated coumarins (7-hydroxy-5, 6-di-methoxycoumarin; 6,8-dihydroxy-5,7-dimethoxycoumarin), gallic acid-derivatives, flavonoids, phenolic and hydroxycinnamic acid-derivatives (Kayser and Kolodziej, 1995; Kolodziej, 2007; Colling et al., 2010) . Recently, 6-Methoxy-7-(sulfooxy)-2H-1-benzopyran-2-one and 6,8-Bis(sulfooxy)-7-methoxy-2H-1-benzopyran-2one were identified in Pelargonium sidoides for the first time (Hauer et al., 2010) . Most significantly, Hauer et al. (2010) characterised two novel compounds, 7-Hydroxy-6-methoxy-8-(sulfooxy)-2H-1-benzopyran-2-one and 8-Hydroxy-7-methoxy-6-(sulfooxy)-2H-1-benzopyran-2-one (Fig. 2) . These novel compounds have to be screened for pharmacological activity as they may represent the individual active constituents that have so far remained elusive.
It is interesting to note that the repertoire of health conditions for which Pelargonium sidoides is used has expanded beyond the original traditional uses against gastrointestinal disorders to include respiratory tract infections such as acute bronchitis, asthma, sinusitis and tonsilllopharyngitis. Accordingly, most of the experimental and clinical research has focused on the treatment of respiratory tract infections in line with the development of the phytopharmaceutical, EPs s 7630 (Umckaloabo s ). In this regard, a wide array of pharmacological studies involving in vitro (Table 1 ), in vivo (Table 2) and randomised, double-blind, placebo-controlled clinical trials (Table 3) has been conducted. Concomitantly, a diverse range of test systems has been used to evaluate the pharmacological properties of Pelargonium sidoides. The approaches, which are characterised by different levels of complexity, including the antimicrobial microdilution assay, anti-adhesion assay using HEp-2 cells, penicillin/gentamicin-protection assay, neuraminidase inhibition assay, fibroblastvirus protection assay and reverse transcription-polymerase chain reaction (RT-PCR) assay have helped in deciphering the pharmacological efficacies as well as the possible modes of action involved in the healing processes.
Pelargonium sidoides extracts have been tested and exhibited good activity against a number of viruses, including influenza A viruses (H1N1, H3N2), coxsackie A9 virus, human coronavirus, respiratory syncytial virus (RSV), parainfluenza virus 3 and herpes simplex viruses (HSV-1, HSV-2) (Table 1) . However, the EPs s 7630 phytopharmaceutical had poor activity (IC 50 ¼ 4100 mg/ml) against the highly pathogenic avian influenza A virus (H5N1) (Michaelis et al., 2011) . Notably, the EPs s 7630 extract had high in vitro activity against H1N1 (IC 50 ¼ 5.4 mg/ml) (Theisen and Muller, 2012 ) and H3N2 (IC 50 ¼ 8.66 mg/ml) (Michaelis et al., 2011) attesting to its use in respiratory health conditions. The authors noted that the EPs s 7630 extract was more active against enveloped viruses compared to nonenveloped viruses (adenovirus 3, adenovirus 7 and human rhinovirus). Interestingly, antiviral bioactivity (EC 50 ) of isolated phenolic constituents against H1N1 increased in the order of complexity of their chemical chain structure as follows: epigallocatechin (42.5 mg/ml)4gallocatechin (28.4 mg/ml)4gallocatechin-(4β-8)gallocatechin (7.3 mg/ml)4epigallocatechin-(4β-8)-gallocatechin (6.3 mg/ml)4oligo-/polymeric fraction (2.8 mg/ml) (Theisen and Muller, 2012) . The study reported a poor direct virucidal activity of EPs s 7630 (250 mg/ml). Instead the authors discovered that the extract and its phenolic constituents imparted anti-viral activity by interfering with virus binding to host cell receptors and through inhibition of the neuraminidase enzyme. Furthermore, the control of viral infections may occur through the production of interferons (IFNs) by the host cells, suggesting that therapy by Pelargonium sidoides may be through the stimulation of the innate immune system (Kolodziej, 2007) . Based on the current state of research using in vitro models it is clear that the mode of action of Pelargonium sidoides in antiviral activity may involve several mechanisms. The mode of action of the antiviral constituents in Pelargonium sidoides has also not been explained using in vivo models, for example Theisen and Muller (2012) only showed that EPs s 7630 increased survival of H1N1 virus-infected mice, but did not explain the underlying mechanisms involved (Table 2) . Further studies incorporating molecular approaches may help to understand the mechanism of action of the antiviral active constituents.
In traditional medicine, extracts of Pelargonium sidoides are used to treat bacterial-related conditions such as diarrhoea, dysentery and tuberculosis (Hutchings et al., 1996) . In South Africa, many plant species are used to alleviate symptoms of tuberculosis caused by Mycobacterium tuberculosis, the fifth largest cause of mortality in the country (McGaw et al., 2008) . Pelargonium sidoides plant extracts have been tested against Mycobacterium species as well as several Gram-positive (Bacillus subtilis, Enterococcus faecalis, Staphylococcus aureus, Streptococcus pyogenes) and Gramnegative (Escherichia coli, Proteus mirabilis, Helicobacter pylori) bacteria. Most notably, EPs s 7630 had moderate in vitro activity against multi-resistant Staphylococcus aureus with a minimum inhibitory concentration (MIC) of 3.3 mg/ml . The same bacterial strains were resistant to common antibiotics such as ciprofloxacin and erythromycin. This study provided a significant finding and highlighted the importance of Pelargonium sidoides as a potential alternative antibacterial remedy at a time when resistance to antibiotics is fast becoming a medical challenge. However, there is need of a paradigm shift towards experimentation that provides more biological insights on the molecular mechanisms involved in the observed in vitro activity. A Pelargonium sidoides butanol extract had higher activity (MIC ¼0.156 mg/ml) compared to that of its isolated chemical entities such as umckalin (MIC ¼ 62.5 mg/ml) against Mycobacterium smegmatis possibly due to synergistic effects (Mativandlela et al., 2007) . The efficacy of a natural product may be due to two or more constituents acting synergistically, whereby their respective bioactivities often diminish or disappear upon separation into individual chemical entities (Li and Vederas, 2009 ). Synergism of bioactive compounds in phytopharmaceuticals is normally claimed to account for their therapeutic effectiveness (Wagner and Ulrich-Merzenich, 2009 ). In particular, polyphenolic compounds in plant extracts are known to increase the pharmacokinetic rate of antiinfective constituents in phytopharmaceuticals thereby enhancing their bioavailability (Wagner, 2011) . In addition, these natural products can also work synergistically with antibiotics thereby improving their overall pharmacokinetic properties against resistant bacterial strains (Schmidt et al., 2007) . However, the moderate MICs suggest that Pelargonium sidoides constituents have no direct effect on the bacteria. Thus, further studies have attempted to elucidate the modes of action of its active constituents. Beil and Kilian (2007) and Conrad et al. (2007b) working on Helicobacter pylori and Streptococcus pyogenes, demonstrated that EPs s 7630 prevents the bacteria from adhering to gastric AGS-cell membranes and HEp-2 cells, respectively. These studies showed that the possible mode of action of the bioactive constituents is through modulation of host-bacteria interactions and phagocytosis, which prevent bacterial attachment to the substrate (gastric and human epithelial cells) thereby rendering the pathogens ineffective. The bioactive constituents of Pelargonium sidoides have been shown to specifically target adhesion factors of the bacteria rather than those of the epithelial cell membranes (Conrad and Frank, 2008) .
Immunomodulatory activities of Pelargonium sidoides and its related phytopharmaceutical medicine may also account for the observed moderate bioactivity against bacteria associated with respiratory diseases through activation of the host cells macrophage machinery. Kayser et al. (2001) demonstrated that murine macrophages infected with Leishmania parasites induced the production of the reactive nitrogen intermediary, inorganic nitric oxide (NO), a known antimicrobial effector molecule. The study showed that gallic acid and the highly oxygenated coumarins, 7-hydroxy-5,6-dimethoxycoumarin (umckalin) and 6,8-dihydroxy-5,7-dimethoxycoumarin were the most potent NO-inducers. Thäle et al. (2008) further proved that activated macrophages obtained from C57BL/6 WT mice were key components of the antimicrobial immune response against Listeria monocytogenes through the production of NO. Compared to the control (2.2 mM), infected cells treated with EPs s 7630 significantly increased release of NO in a dose-dependent response from 1.0 mg/ml (2.8 mM) to 30 mg/ml (5.5 mM). In both models, infected macrophages had a higher NO-inducing effect compared to non-infected macrophages indicating that the nonspecific immune response was triggered under disease attack (Kayser et al., 2001; Thäle et al., 2008) . In Leishmania major-infected macrophage-like RAW 264.7 cells exposed to EPs s 7630, there was a marked up-regulation of inducible nitric oxide synthase (iNOS) gene expression evaluated by reverse transcription-polymerase chain reaction (RT-PCR) Trun et al., 2006) . In diseased cells, the molecular expression of iNOS in activated macrophages stimulates the production of high levels of NO, which is an antimicrobial effector molecule (Nathan and Hibbs, 1991) . In particular, gallic acid, one of the constituents of the EPs s 7630 (Kayser et al., 2001) has been shown to induce prolonged iNOS mRNA expression in Leishmania-infected cells. In addition, release of tumour necrosis factor (TNF-α) and interferons (IFN) provided further evidence for cytokine-induced macrophage activation and plays a crucial role in immune defence mechanisms in infected cells (Reiner and Locksley, 1995) . Experimental data has shown that the TNFinducing potential of Pelargonium sidoides is strongly associated with its phenolic constituents (Kolodziej and Kiderlen, 2007) . The methanol extract of Pelargonium sidoides (25 mg/ml) exhibited negligible TNF-inducing potential ( o0.1 U/ml) compared to the moderate activity of the ethyl acetate (20.2 U/ml) and n-butanol (18.9 U/ml) fractions (Kayser et al., 2001) . Most significantly, gallic acid (6.25-50 mg/ml) led to a high dose-dependent increase in TNF-inducing potency (21-43.7 U/ml) of infected cells. Radtke et al. (2004) also demonstrated the concomitant TNF-α mRNA gene expression in infected cells. On the other hand, gallic acid was shown to increase IFN-α level in Leishmania-infected cells coupled with the up-regulation of IFN-γ mRNA transcripts (Radtke et al., 2004; Kolodziej et al., 2005) . Most notably, umckalin, the signature chemical entity in Pelargonium sidoides exhibited poor cytokine gene expression profiles. Table 2 presents a summary of pharmacological evaluations using in vivo animal models. Despite the importance of animal models in the evaluation of pharmacological efficacy, only a few studies have utilised this system for Pelargonium sidoides and/or its related formulations. Good research practice for plant-derived medicines dictates that in vitro tests should be backed up with in vivo and ultimately clinical studies (Houghton et al., 2007) . More studies on Pelargonium sidoides should adopt this approach so as to avoid the pitfalls associated with extrapolating in vitro test results to claim in vivo activity and efficacy. Cos et al. (2006) argued that animal models are indispensable in validating in vitro activity because they take into account pharmacokinetic, metabolic and toxicological phenomena. Based on this approach, Yu et al. (2010) , Tian et al. (2011) and Li et al. (2013) used in vitro and in vivo antiviral models thereby obtaining comprehensive pharmacological data including efficacy and toxicology of several Chinese herbal medicines. Recently, Theisen and Muller (2012) confirmed in vitro antiviral activity of EPs s 7630 using an in vivo animal model system. Therefore, both in vitro and in vivo models should be considered in future Pelargonium sidoides anti-infective research. In addition, the research can also focus on developing better in vivo model systems to elucidate the actual mechanisms involved in the therapeutic processes of Pelargonium sidoides, which have so far remained unclear.
The phytopharmaceutical, EPs s 7630 has undergone numerous clinical evaluations in randomised, double-blind, placebo-controlled trials. Incidentally, it has been clinically evaluated against respiratoryrelated conditions, namely acute bronchitis, acute rhinosinusitis, common cold, chronic obstructive pulmonary disease and asthma ( Table 3 ). The clinical trials conducted for EPs s 7630 have included patients of all ages. The reported results suggest that the Pelargonium sidoides herbal medicine may be effective in the treatment of respiratory infections caused by bacteria and viruses. Among the common respiratory tract infections, most of the clinical studies have evaluated the phytopharmaceutical against acute bronchitis in placebo-controlled studies. Acute bronchitis is characterised by acute inflammation of the respiratory tract and is caused by viral infections in 95% of the cases (Matthys and Heger, 2007b ). However, more clinical studies have to be done to determine its efficacy in the treatment of other common respiratory diseases. Despite the limited benefit of antibiotic therapy for acute bronchitis, they are prescribed in 60-80% of the cases (Matthys and Heger, 2007a) . Against this background, more appropriate treatment options are required so as to prevent the overuse and/or abuse of antibiotics. In this regard, phytopharmaceuticals such as Pelargonium sidoides-based products may provide an alternative therapeutic option in the treatment of respiratory tract infections and related ailments.
It is of paramount importance that medicinal plants and phytopharmaceuticals are safe and do not cause undesirable side effects in patients. However, despite its long history of use in traditional medicine, there is a dearth of scientific information pertaining to the safety evaluation of Pelargonium sidoides. The Pelargonium sidoides extract, EPs s 7630, did not cause obvious toxic effects in mice as there were no significant differences in body weight, body temperature as well as organ weight (lungs, liver, spleen, kidneys) between the treatment and control groups (Theisen and Muller, 2012) . Based on clinical data, the tolerability of treatment with EPs s 7630 has been shown to be good in both adults and children (Table 3) . Nevertheless, some of the commonly reported adverse events included gastrointestinal complaints such as diarrhoea (Matthys et al., 2003 (Matthys et al., , 2007 (Matthys et al., , 2013 Haidvogl and Heger, 2007; Matthys and Heger, 2007a; Bachert et al., 2009; Kamin et al., 2010 Kamin et al., , 2012 , nervous system complaints (Matthys et al., 2003) , respiratory and mediastinal ailments (Matthys et al., 2003) , ear and labyrinth complaints (Matthys et al., 2003) , exanthema (Haidvogl and Heger, 2007) , tracheitis and epistaxis (Lizogub et al., 2007) and allergic skin reactions (Bachert et al., 2009) . Recently, a clinical study by Teschke et al. (2012) concluded that Pelargonium sidoides did not reveal evidence of hepatotoxicity. However, even though the adverse events in most clinical studies have been reported as non-serious, more rigorous studies are still required to ascertain the safety of Pelargonium sidoides and its related formulations. In addition, further toxicological studies involving toxicity and mutagenic tests need to be done to evaluate the safety of this plant. Although the benefits of medicinal plants are widely acknowledged, the need for safety evaluation remains critical so as to distinguish between toxic effects and pharmacological efficacy of plant extracts . Based on the numerous studies reported in the current review, there is compelling experimental and clinical evidence to suggest that Pelargonium sidoides may be efficacious against respiratory tract infections and may be safe for both adults and children, but more stringent toxicological studies are required. Verschaeve and Van Staden (2008) have comprehensively discussed the various methods that are used in evaluating the safety of medicinal plants.
Besides its local use as a multipurpose traditional remedy, Pelargonium sidoides has evolved into an international phytopharmaceutical. The commercialisation of Pelargonium sidoides dates back to the early 1900s when the plant was introduced in Europe as a tuberculosis remedy by Charles Henry Stevens after being reportedly cured by a traditional healer in Lesotho (Bladt and Wagner, 2007; Brendler and van Wyk, 2008; Wynberg et al., 2012) . The growing international demand for the Pelargonium sidoides root extract has led to an increase in the number of gatherers as well as the volume of harvested plant materials. Its evolution from a traditional medicine exclusive to southern Africa, mainly South Africa and Lesotho, into a successful phytopharmaceutical (Umckaloabo s ) has created 'the Pelargonium industry' involving a network of harvesters, local buyers and processors and international pharmaceutical manufacturers, such as Dr. Willmar Schwabe GmbH & Co., KG Pharmaceuticals (Karlsruhe, Germany) . Pelargonium trade has evolved from a largely unregulated to a more formalised industry over the past 20 years . An unknown number of harvesters in the Eastern Cape (South Africa) and Lesotho collect and sell the plant materials to local intermediary buyers Newton et al., 2013) . The organisation of trade in medicinal plants normally involves a chain of local dealers buying plant materials from local collectors and eventually selling to larger trading and export companies (Lubbe and Verpoorte, 2011) . In the Eastern Cape, Gowar Enterprises collects and supplies the Pelargonium sidoides tuberous roots to another intermediary, BZH Import and Export, responsible for drying, shredding, packaging and onward routing to Parceval Pharmaceuticals, which exports the materials to the end-product manufacturer in Germany . In Lesotho, Bophelo Processing is responsible for collecting, processing and supplying of the tubers to Parceval Pharmaceuticals . The processing of the raw materials obtained from developing economies involved in the medicinal plant trade is still predominantly undertaken in European countries by end-product manufacturers (Lubbe and Verpoorte, 2011) and this also applies to Pelargonium sidoides.
The commercial success of Umckaloabo s provides a good example of what can be achieved with a well-directed research and development initiative and astute marketing (Gericke, 2011) . Most of the harvesters mainly rely on wild collection of Pelargonium sidoides for their livelihoods due to limited alternative economic opportunities in these communities. Amidst the overall commercial success of the Pelargonium trade, questions have been asked about the possible vulnerability of the harvesters and their lack of bargaining power arising from the monopolistic marketing chain . Large trading companies have significant control over the pricing system due to their central role in the medicinal plant trade coupled to large scale purchases and ownership of critical infrastructure to perform several functions including quality control (Lubbe and Verpoorte, 2011) . However, despite these challenges related to beneficiation equity from medicinal resources, lessons arising from the Pelargonium sidoides case study are clearly invaluable for future natural product research and development programmes in developing countries. An increasing number of medicinal plant suppliers in China, India, Mexico and Malaysia are now exporting processed products to end-product manufacturers in Western countries (Lubbe and Verpoorte, 2011) . The 'Pelargonium industry' may have to evolve in tandem to this growing trend in the medicinal plant trade.
The increasing commercial demand for Pelargonium sidoides on the international market has led to localised uncontrolled, indiscriminate and sometimes illegal harvesting of wild plants (Lewu et al., 2006 (Lewu et al., , 2007 Wynberg et al., 2012) . The escalation in demand can cause irreparable reductions to wild populations (Colling et al., 2010) , which may result in a biodiversity threat to Pelargonium sidoides. However, the conservation status of Pelargonium sidoides was recently revised from 'declining' (Red Data List of South African Plants, 2009) to 'least concern' (Red Data List of South African Plants, 2013). In Lesotho, the conservation status of Pelargonium sidoides has not been evaluated. In addition, the plant is not listed on either the International IUCN Red List of Threatened Species or Convention on International Trade in Endangered Species (CITES) database (Newton et al., 2013) .
There is a conspicuous lack of comprehensive data on annual harvested and traded volumes of Pelargonium sidoides. Varying estimates derived from data collected through interviews have been reported in literature. The estimates of annual harvested fresh material range from 9 to 45 t (Newton et al., 2013) and 26-440 t (Van Niekerk and Wynberg, 2012) . Despite this lack of accurate data, tight conservation regulations have been formulated to curb uncontrolled harvesting in South Africa (Newton et al., 2013) . Notwithstanding the occasional financial returns obtained by the local communities, the overexploitation of the resource may affect its availability in the future. In the Eastern Cape, the plants had a slow regeneration rate, which was significantly lower than the initial harvest after the second year (Lewu et al., 2007) . To meet the ever-expanding demand in international trade of raw materials, Pelargonium sidoides may have to be cultivated on a large scale. Currently, the plant is only cultivated on a small, negligible scale (Colling et al., 2010) . There are also limitations in the use of seed propagation, due to their low viability coupled with low germination (Lewu et al., 2006) .
Alternatively, biotechnology tools such as plant tissue culture (Fig. 1D ) may play a critical role in the provision of genetically uniform clones for the Pelargonium industry (Moyo et al., 2013) . Recently, Kotzé (2011) , Moyo et al. (2012) and Moyo et al. (in press) reported on micropropagation and acclimatisation procedures with the capacity to produce millions of uniform Pelargonium sidoides clones throughout the year. There is a long history of the commercial production of high-value phytochemicals using tissue culture systems (Canter et al., 2005) . However, a major challenge with the cultivation of medicinal plants is the perception that such plants do not produce a similar quality of bioactive compounds as wild plants. White et al. (2008) and Moyo et al. (2013) showed that greenhouse produced plants had similar bioactive compounds as wild plants in terms of the umckalin (6-hydroxy-5,7-dimethoxycoumarin) and phenolic compounds, respectively. In addition, extracts of greenhouse and wild plants exhibited comparable antimicrobial and antioxidant properties (Moyo et al., 2013) . In the long term, the production of Umckaloabo s may have to be based on plant material produced under consistent cultivation practices. Such cultivated material produced under controlled environmental conditions is preferred for the phytopharmaceutical industry as it minimises qualitative and quantitative variations in the composition of natural products (Lubbe and Verpoorte, 2011) . In addition, the quality of phytopharmaceuticals can be improved by the use of genetically uniform clones, which eliminates problems associated with product adulteration (Schmidt et al., 2007) .
On the other hand, the future pharmaceutical production of Umckaloabo s may also eventually depend on the application of bioreactor technology in the synthesis of Pelargonium sidoides bioactive compounds. Colling et al. (2010) demonstrated the ability of transgenic Pelargonium sidoides hairy root cultures, transformed using Agrobacterium rhizogenes, to produce the desired bioactive pharmaceutical compounds. The authors concluded that the system has immense potential as a conservation strategy for this medicinally important plant. However, there is a possibility that phytotherapeutics produced using biotechnology may not be readily acceptable by consumers of 'natural' medicines. Notwithstanding these concerns, it may be inevitable that biotechnology will play a key role in the production of plant-derived pharmaceutical compounds in the future. Hairy root cultures which are transformed using Agrobacterium rhizogenes often sustain stable and high productivity in plant growth regulatorfree medium (Canter et al., 2005) . Thus, the use of biotechnology approaches can allow for ease of standardisation of the chemical constituents of the phytopharmaceutical thereby guaranteeing consistent quality of the end-product. Overall, this will help to avert the current plant biodiversity conservation dilemma arising from overharvesting practices of wild populations. 
Despite the emergence, in recent times, of high-throughput screening of synthetic chemical libraries as an alternative technology for the pharmaceutical industry, natural products remain a vital component in drug discovery. In particular, medicinal plants offer several advantages as potential sources of both novel chemical entities and phytopharmaceuticals. The pharmacological activities that have been demonstrated in various in vitro, in vivo and clinical studies indicate that Pelargonium sidoides possesses moderate direct anti-infective properties but highly notable immunomodulatory activity. In addition, Pelargonium sidoides root extract is effective and well tolerated in the treatment of respiratory-related infections. Based on both experimental and clinical pharmacological evidence, the transformation of Pelargonium sidoides from a traditional medicine to a successful phytopharmaceutical provides a compelling argument for the continued exploration of medicinal plants and indigenous medical systems for the next generation of phytopharmaceuticals. Even though significant milestones have been achieved in Pelargonium sidoides pharmacological research, further studies are still needed to fully elucidate the mechanisms of action and the biological principles underlying its therapeutic capacity. Most notably, the bulk of the pharmacological research on Pelargonium sidoides has been skewed towards respiratory tract infections at the expense of ailments for which the plant is used in Traditional African Medicine. Clinical research should also focus on other respiratory tract infections besides acute bronchitis, which has so far attracted the most attention. Furthermore, there is lack of conclusive data on the toxicological properties of Pelargonium sidoides despite having been used in traditional medicine for a long time. Stringent evaluation of the toxicological properties of Pelargonium sidoides is of paramount importance given its extensive use in medicinal formulations.
In the long term, the successful commercialisation of this southern African medicinal plant must be viewed in a much wider and holistic context that includes conservation-friendly practices and the sustainable supply of raw materials. In that context, the sustenance of the Pelargonium sidoides phytopharmaceutical industry will require innovative approaches, which utilise biotechnology tools such as plant tissue culture and bioreactors for the production of genetically uniform clones and therapeutic secondary metabolites, respectively.