Leaf Oils of the Australian Species of Decaspermum (Myrtaceae), The

Journal of Essential Oil Research: JEOR, Nov/Dec 2005 by Brophy, Joseph J, Goldsack, Robert J, Forster, Paul I

Abstract

The leaf oils of the two Australian species of Decaspermum have been examined by GC and GC/MS. The leaf oil of D. struckoilicum contained α-pinene (37.5%) as its principal component in an oil that contained similar amounts of mono- and sesquiterpenes. The major sesquiterpenes identified in the oil were β-caryophyllene (2.4%), α-humulene (2.2%) and α- and β-eudesmol (8.2% and 8.1%, respectively). Decaspermum humile produced a leaf oil that contained either approximately equal amounts of mono- and sesquiterpenes or had a majority of the latter components. The principal monoterpenes were α-thujene (0.1-13%) and α-pinene (0.2-21 %). Other prominent monoterpenes identified were limonene (0.2-8%), myrcene (0.3-10%), β-phellandrene (0.1-5%), linalool (0.3-9%) and terpinen-4-ol (0.3-6%). 1,8-Cineole was usually absent from the oils. The main sesquiterpenes identified in the oils were β-caryophyllene (0.7-5%), aromadendrene (1-6%), viridiflorene (1-7%), δ-cadinene (0.4-14%), bicyclogermacrene (0.2-10%), globulol (1-9%) and in some collections 7-epi-α-selinene (trace-9%).

Keyword Index

Decaspermum humile, Decaspermum struckoilicum, Myrtaceae, essential oil composition, α-thujene, α-pinene, bicyclogermacrene, δ-cadinene.

Introduction

The genus Decaspermum J.R.Forst. et G.Forst. comprises about 30 species of shrubs or small trees that occur in Asia, Malesia, Melanesia and eastern Australia (1-3). Decaspermum is included in the Myrtinae and is allied to genera such as Archirhodomyrtus Burret, Austromyrtus (Nied.) Burret, Cassia N.Snow et Guymer, Lenwebbia N.Snow et Guymer, Lithomyrtus F. Muell., Lophomyrtus Burret, Myrtella F.Muell., Myrtastrum Burret, Neomyrtus Burret, Octamyrtus Diels, Pilidiostigma Burret, Rhodamnia Jack, Rhodomyrtus (DC.) Rchb. and Uromyrtus Burret (3), although a phylogeny for this alliance is yet to be presented.

Two species of Decaspermum occur in Australia (4). Decaspermum humile (G.Don) A.J.Scott (syn. D. parviflorum (Lam.) A.J.Scott) (Silky Myrtle) is widespread in eastern Australia from northeastern New South Wales to Cape York in Queensland and also occurs in Malesia. This species is a shrub up to 15 m tall and occurs in a variety of evergreen to semideciduous rainforest communities, e.g. microphyll vinethicket and microphyll and notophyll vineforests, on a variety of substrates. By comparison, the second species D. struckoilicum N.Snow et Guymer is a rare endemic restricted to a small area near Mt Morgan in central Queensland. Decaspermum struckoilicum is a shrub to 5 m high and occurs in semi-evergreen vinethicket on volcanic soils.

The leaf oils of both species have not been previously examined. There is a report, from Fiji, of the oil composition of D. vitiense [syn. D. fruticosum] which states that the oil contains "α-pinene as the major component alongwith β-pinene, cineole and terpineol" (5). We are, in addition, able to compare the results presented here to other genera in the Myrtinae group such as Archirhodomyrtus (6), Austromyrtus (7,8), Gossia (8-10), Lenwebbia (8,11), Pilidiostigma (12), Rhodamnia (13), Rhodomyrtus (14) and Uromyrtus (15).

Materials and Methods

Leaf material of D. humile was collected from the following locations in Queensland, usually from two individual plants with a bulk sample from a further three plants. D. stuckoilicum was from a bulk collection. AE PIF collection vouchers are deposited at the Queensland Herbarium (BRI).

Decaspermumhumile: PIF15673, near Orchid Grotto, Lamington N.P., 28°14'S, 153°08'E; PIF16837, Leo Creek Mine Area, 13δ44'S, 143°22'E; PIF15258, Kirrama Range, 18°12'S, 145°51'E; PIF15355, Captain Billy Landing turnoff, 11°41'S, 142°41'E; PIF15395, Garraway Creek, 12°43'S, 143°08'E; PIF15490, Bridle Creek L.A., S.F. 607, Dinden, 16°58'S, 145°35'E; PIF15512, Little Mossman L.A., S.F. 143,16°31'S, 145°22'E. Decaspermum struckoilicum: PIF20268, Struck Oil, 23°37'S, 150°27'E.

Isolation of oils: The leaf oils were isolated by hydrodistillation with cohobation as previously outlined in (16). Analyses of the oils were carried out by gas chromatography and combined gas chromatography/mass spectrometry. The oil yields quoted below are weight/weight, based on fresh material.

Identification of components: Analytical gas chromatography (GC) was carried out on a Shimadzu GC17 gas chromatograph. Either a SCOT column coated with FFAP or a WCOT DB-Wax (60 m x 0.5 mm, film thickness 1 µm) was used. In both cases the column was programmed from 50°-225°C at 3°C/min with helium at 3.5 mL/min as carrier gas. GC integrations were performed on an SMAD electronic integrator without the use of correction factors. GC/MS was performed on a VG Quattro mass spectrometer operating at 70 eVionization energy; the column used was DB-Wax (60 m x 0.32 mm, film thickness 0.25 µm) programmed from 35°-220°C at 3°C/min, with helium at 35 cm/s as carrier gas. Compounds were identified by their identical GC retention times to known compounds and by comparison of their mass spectra with either known compounds or published spectra (17-21).