Salvia stenophylla Burch. ex Benth. (Lamiaceae) is a perennial odorous herb, which is endemic to southern Africa occurring from central Namibia to southwestern Botswana and in many parts of South africa. It is closely related to Salvia runcinata L. f. and Salvia repens Burch. ex Benth. with which it forms a species complex. L.E Codd last revised the three taxa in 1985 in which characters used to delimit the taxa include size of corolla, calyx and trichome density. The specific limits between the three taxa are not clear because of intergrading morphological characters, which make it difficult to distinguish them from one another. Therefore in this regard, taxonomic delimitation by chemical analysis was the main objective of this research. The taxa represented in this species complex are known in folk medicine and plant extracts have been used in the treatment of urtricaria, body sores, and stomach ailments and as a disinfectant. S. stenophylla is reported to contain α-bisabolol, a compound that has anti-inflammatory properties. Based on the traditional uses of these plants and the international use of α-bisabolol to develop active cosmetic products, establishing a scientific rational for the uses was another objective.
Plant material was collected from a total of twenty-six different natural populations (9 populations of S. stenophylla; 5 of S. repens and 14 of S. runcinata). Trichome study was undertaken using scanning electron microscopy (SEM). The aerial parts of the plants were hydrodistilled to extract essential oils (volatile compounds) and analytical assessment of the oil was carried out using thin layer chromatography (TLC), gas chromatography (GC) and gas chromatography coupled to mass spectrophometry (GC-MS). Non-volatile compounds were extracted using methanol and then analyzed by TLC and high performance liquid chromatography (HPLC-UV-MS). For the documentation of biological activity, antimicrobial activity assays, antioxidant activity by TLC-DPPH assay and anti-inflammatory activity by COX-2 assay were performed. To investigate the source of chemical variations that were observed, seeds from selected populations were cultivated, harvested and distilled upon maturity. A molecular study attempted to evaluate genetic differences amongst individual plants and populations using the amplified fragment length polymorphism (AFLPs) technique.
The SEM results did not reveal variation of the types between the different taxa. TLC and GC/MS results showed immense variation in the qualitative and quantitative chemical composition within and between populations of the same and different taxa. The dominant compounds in S. stenophylla include; α-bisabolol (46.5%), limonene (38.1%), δ-3-carene (24.9%), γ-terpinene (20.3%), p-cymene (18.4%) and (E)-nerolidol (53.6%). S. repens accumulated major compounds like (E)-nerolidol (25.2%), ledol (25.4%), camphor (12.7%), β-caryophyllene (13.6%) and β-phellendrene (22.2%). S. runcinata has (E)-nerolidol (72%), α-bisabolol (41.1%), limonene (24.1%), α-pinene (45%) and β-pinene (15%) and 26% of guaiol in high percentages, and three chemotypes were identified. The HPLC-UV-MS results revealed the occurrence of rosmarinic acid, carnosic acid, carnosol, isocarnosol and oleanolic acid derivatives in all the methanol extracts analysed. This was also portrayed in the TLC-DPPH assay. The chemical variation was also expressed in the biological activity assays that were performed. S. stenophylla extracts exhibited high antibacterial activity against gram (+) bacteria and high anti-inflammatory activity in the essential oils. The AFLP results showed congruency with the chemical composition data as it supported the erratic chemical variations within the species complex. In view of all these results, we concluded that the three taxa are closely related with the existence of intermediates (hybrids) within the species complex.