Abstract
The genus Senecio (Asteraceae) holds significant medicinal, toxicological, and forensic importance in South Africa and other African countries. While many species are used as food or medicine, several others accumulate macrocyclic pyrrolizidine alkaloids, which are hepatotoxic, pneumotoxic, genotoxic, and carcinogenic to humans and animals when consumed in large quantities or in sub-lethal doses over extended periods. Unfortunately, toxic species have, for various reasons, contaminated food products or medicines, leading to several illnesses and indeed also fatalities in adults and children. Pyrrolizidine alkaloids cause veno-occlusive disease, which is nowadays referred to as sinusoidal obstruction syndrome (SOS).
This study aims to contribute to our understanding of the ethnobotanical and toxicological relevance of South African Senecio species. The objectives are to conduct a comprehensive ethnobotanical review of the literature; perform phytochemical analyses to determine the presence or absence of toxic alkaloids, as well as phenolic compounds that may have diagnostic value; compile a list of Senecio species used in traditional medicine in South Africa, and highlight which species are toxic and which ones are not. A further objective was to explore methods of chemical analysis and to suggest a strategy to eventually, in the interest of public safety, document the full chemical variation in South African species.
Among the 283 species and infraspecific taxa of Senecio found in South Africa, 52 have been documented in the literature for their ethnobotanical uses. These uses include food and medicine, as well as veterinary and ceremonial applications. Depending on the specific medicinal use, these species are utilised internally or externally to treat various illnesses and disorders.
Observations at muthi markets (muthi means traditional medicine) in Johannesburg identified 28 medicinal species, of which only 54% (28/52) were recognised for their
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previously documented and ritual uses, while 46% (24/52) remained unidentified due to morphological similarities, incomplete material and ambiguous common names. Accurate studies of muthi market materials are not possible without detailed information about the plants, their morphological characters (e.g., leaves and inflorescences) and their geographical origins. According to the traders, medicinal preparations are predominantly administered orally as decoctions or topically as poultices.
The study identified substantial quantities of retrorsine N-oxide, as the most common pyrrolizidine alkaloid, in 100 Senecio species that were screened using High Performance Liquid Chromatography (HPLC) coupled with a diode array detector (DAD). Notably, 11 species exhibited high concentrations (0.1–2.4% g/g) of retrorsine N-oxide, exceeding levels of other alkaloids such as seneciphylline N-oxide, senecionine N-oxide, and retrorsine. These results raise concerns about the potential health risks of pyrrolizidine alkaloids and the difficulty of identifying Senecio species, so that toxic species may be mistaken for the ones that can be safely used.
In addition to alkaloids, an exploratory HPLC analysis generated a comprehensive dataset of non-alkaloid compounds, which was followed up by a detailed phytochemical profiling of a selection of 12 medicinally used Senecio species through Ultra Performance Liquid Chromatography-Mass Spectrometry (UPLC-MS). This analysis revealed the presence of flavonoid glycosides, including isorhamnetin, kaempferol, and quercetin derivatives, as well as organic acids such as caffeoylquinic, chlorogenic, and quinic acids. Furthermore, flavonoids such as apigenin and cirsiliol were identified. In the pyrrolizidine alkaloid analysis, 7-angeloylretronecine and its N-oxide, acetyl erucifoline, bisline, budelphine, codonopsinol A, cusohygrine, erucifoline and erucifoline N-oxide, jacoline, junceine, neoplatyphylline, niazimin, osthole, platyphylline, retrorsine and retrorsine N-oxide, and trichodesmine and its isomers were tentatively identified based on mass spectral data. Using reference standards for direct comparisons, the identity of several common Senecio alkaloids could be confirmed. Additionally, phenolic compounds which were detected along with these alkaloids were phenolic acids, sesquiterpenes and coumarins, emphasising the diverse phytochemical profile of Senecio species and their potential
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applications in chemotaxonomic, chemophenetic and forensic studies.
The study revealed the chemical complexity of South African Senecio species, showing that it may be feasible to develop a comprehensive chemophenetic inventory using modern LC-MS technology. Such an inventory will require authentic reference samples of both the species and the chemical compounds (especially pyrrolizidine alkaloids, phenolic acids, sesquiterpenoids, coumarins and flavonoids) and correctly interpreted diagnostic characters (from both morphology and phytochemistry). Challenges would include: (1) Comprehensive sampling of large numbers of individual plants, populations and species to cover the full range of possible chemical diversity within the species; (2) The taxonomic expertise to identify all indigenous Senecio species in situ (particularly those that are of ethnobotanical relevance) to ensure authentic samples, authentic use-records and reliable phytochemical data; (3) The phytochemistry expertise to interpret mass fragmentation patterns and develop a library of mass spectral data.
Acute, chronic and sometimes fatal poisoning of humans and animals remains a real threat (as evidenced by recent examples). There is a need to inform the public, and especially traditional health practitioners, of the dangers of misidentification and the indiscriminate use of Senecio species outside the cultural safety boundaries of long-established traditional knowledge.