The essential oil composition and chemotaxonomical appraisal of South African Pelargoniums (Geraniaceae)

Abstract

A plethora of information is available on the essential oil composition of commercially grown Pelargonimus namely P. capitatum, P. graveolens and P. radens and their hybrids, while only a few chemical investigations have been carried out on the other aromatic Pelargonium species indigenous to South Africa. The hydrodistilled leaf oils of 13 South African Pelargonium species of the genus Pelargonium (family Geraniaceae) were analyzed by means of GC and GC/MS and a total of 315 compounds were identified. The oil data was chemotaxonomically informative confirming taxonomic relationships i.e. between P. graveolens and P. radens, P papilionaceum and P. vitifolium and between P panduriforme and P quercifolium. The oil compositions of P citronellum, P papilionaceum and P vitifolium were different with respect to those of the other analyzed species in this study. Geranic acid was the most abundant oil constituent (36.0%) in P citronellum (provenance NBG), which was the only species in which neral (17.4%) and geranial (27.2%) were detected. Citronellic acid dominated in the oils of P. papilionaceum (provenance NBG) and P vitifolium (provenance SBG), occurring in amounts of 96.2% and 74.7%, respectively. The major monoterpene identified in P. radens (provenance NBG) and in the samples of P graveolens (provenances SBG and (WSBG) was isomenthone (84.5%, 65.8% and 83.3%, respectively). The P. tomentosum oil samples produced an essential oil rich in menthone (36.1-41.1%) and isomenthone (49.3-56.6%). The latter monoterpenic ketone,vas responsible for the chemical affinity demonstrated among P. graveolens, P. radens and P tomentosum. p-Cymene was the principle component (37.6-45.4%) in both samples of P panduriforme. It was also the major compound (54.9%) in P. quercifolium (provenance WSBG) followed by lesser amounts of viridiflorol (13.0%) and spathulenol (5.9%). Pelargonium quercifolium (provenance SBG) and P capitatum (provenance WSBG) were characterized by a high viridiflorol content (24.0-36.6%). Pelargonium glutinosum (provenance SBG) was closely associated with the latter species; its oil was typified by oxygenated sesquiterpenes namely caryophyllene oxide (6.3%), spathulenol (6.9%) and viridiflorol (8.9%). Citronellyl formate (31.1%), citronellol (9.9%) and furopelargone B (6.1%) were most abundant in P capitatum (provenance Strand). Pelargonium hispidum oil (provenance SBG) was characterized by decanoic acid (47.0%) and 2-decenoic acid (31.3%). Pelargonium scabrum produced an oil rich in 14-hydroxy-beta-caryophyllene (27.9%). Pelargonium scabrum was associated with P. betulinum (provenance NBG) which was characterized by the oxygenated sesquiterpene T-cadinol (18.9%).