Commercial production and trade in Sceletium tortuosum and its products is on the rise due to an increase in consumer demand. Mesembrine-type alkaloids are the main active compounds responsible for the therapeutic properties of the plant. In this investigation, GC–MS was used to evaluate the variability in the mesembrine-type alkaloid content of 151 specimens of S.tortuosum growing wildly in 31 localities in the south-western region of South Africa. In addition, the variability of the mesembrine-type alkaloid content of eight commercial products was determined. The total alkaloid content of wild plant material was found to vary between 0.11 and 1.99% of dry weight. Hierarchical cluster analysis and principal component analysis grouped the plants growing in the wild into five main chemotypes (A, B, C, D and E). Chemotype A is represented by samples devoid of mesembrine-type alkaloids, while chemotypes B, C and E are characterised by high levels of mesembrenol (64.96 – 95.55%), mesembrine (51.25 – 92.50%) and mesembrenone (50.86 – 72.51%), respectively. Chemotype D is an intermediate cluster representing specimens containing all four alkaloids in moderate amounts. Qualitative differences in the alkaloid profiles were observed between and within different populations of S.tortuosum, as well as among the investigated products. Mesembrine was identified as the main alkaloid constituent in most of the commercial products analysed. Mesembrenol, mesembrine and mesembrenone can be used as marker compounds for quality monitoring of S. tortuosum raw materials and products.