An Investigation of the Leaf Oils of the Western Australian Broombush Complex (Melaleuca uncinata sens. lat.) (Myrtaceae)

Abstract

The leaf oils of the 11 recorded Western Australian species of the broombush complex of the genus Melaleuca have been examined by a combination of GC and GC/MS. Melaleuca atroviridis produced a monoterpenic leaf oil with α-pinene (11.0%) and 1,8-cineole (73.2%) being the principal components. Melaleuca concreta showed the presence of three chemotypes, one of which was rich in terpinen-4-ol (35.4%), while a second was rich in 1,8-cineole (58–81%). A third chemotype contained signifcant amounts of α-pinene (16.7%), 1,8-cineole (28.4%) and globulol (11.3%). Melaleuca exuvia produced a monoterpenic oil, which appeared to exist in two chemotypes, which contained α-pinene (13–23%), 1,8-cineole (56–67%), terpinen-4-ol (0.1–2%) and α-terpineol (3–7%) in one form and α-pinene (5–7%), 1,8-cineole (28–38%), terpinen-4-ol (11–17%) and α-terpineol (3–4%) in the second form. Melaleuca hamata produced a leaf oil that was dominated by monoterpenes. There appeared to be two chemotypes present, one in which terpinen-4-ol (41.6%) was the major component and a second chemotype in which 1,8-cineole (40.0%) and linalool (33.9%) were the principal components. Melaleuca interioris (from one population) contained a mixture of mono- and sesquiterpenes, in which sesquiterpenes predominated. Melaleuca osullivanii gave a leaf oil in which sesquiterpenes predominated, the principal component being spathulenol (10–18%). Melaleuca scalena produced a leaf oil dominated by monoterpenes, with α-pinene (25–31%) and 1,8-cineole (43–55%) being the principal components. Melaleuca stereophloia was dominated by monoterpenes of which the principal component was 1,8-cineole (78–83%). Melaleuca uncinata sens. strict. existed in a variety of forms one of which had major amounts of 1,8-cineole (44–56%), while a second contained major amounts of terpinen-4-ol (21–31%), γ-terpinene (10–14%) and α-terpinene (6–8%). Melaleuca vinnula appeared to exist in two chemotypes, one of which was rich in α-pinene (65.3%), while the second chemotype was rich in 1,8-cineole (60.6%). Melaleuca zeteticorum produced a leaf oil that was overwhelmingly monoterpene in character, the principal component being 1,8-cineole (63–68%).