Leaf Oils of the Australian Species of Hedycarya (Monimiaceae), The

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

Abstract

The steam distilled leaf oils of Hedycarya angustifolia and H. loxocarya have been investigated by GC and GC/MS. All samples of H. angustifolia examined gave oils in which the major compounds were elemol and α-, β- and γ-eudesmol. Within these samples, however, there were variations. In this species there were observed three chemical varieties: (a) one with no monoterpenes, (b) one with significant quantities of camphene present and (c) samples in which significant amounts of the sesquiterpene hydrocarbon ishwarane were present in the oil. Hedycarya loxocarya gave a leaf oil similar to that given by variety (a) of H. angustifolia, in that the principal components were elemol and α-, β- and γ-eudesmol and virtually no monoterpenes. Solvent extraction of leaf material of both species showed that elemol was the principal component and if the extraction was carried out in the presence of base no eudesmols were detected.

Keyword Index

Hedycarya angustifolia, Hedycarya loxocarya, Monimiaceae, essential oil composition, elemol, α-eudesmol, β-eudesmol, γ-eudesmol, camphene, ishwarane.

Introduction

The family Monimiaceae is grouped in the Laurales and is thought to be most closely related to the families Lauraceae and Hernandiaceae (1,2). Species of Monimiaceae are distributed in the tropics and subtropics of the southern hemisphere and are mainly trees or shrubs, with some lianes (3,4). Although there is reliable fossil pollen of the Monimiaceae only to the Oligocène (4), the family is thought to be of more ancient lineage and amongst the oldest known flowering plants (2).

Six genera and more than 25 species of Monimiaceae are found in eastern Australia (5). Genera with species native to Australia that were formerlyincludedin Monimiaceae subfamily Atherospermatoideae (3,4), such as Atherosperma LabilL, Daphnandra Benth., Doryphora Endl. and Dryadodaphne S.Moore are now included in the separate family Atherospermataceae (2,5).

The genus Hedycarya J.R.Forst. et G.Forst. currently comprises 11 species found in eastern Australia (two ssp.), New Zealand (one sp.) and New Caledonia (eight spp.) (6). Species of Hedycarya are invariably dioecious shrubs or small trees and are characterized by the upper part of the female flower not falling away as a calyptra, the male and female flower receptacles being similar and more or less flat with an entire rim or very small tepals. Hedycarya is currently included in the monimiaceous subfamily Mollinedioideae Thorne, tribe Hedycaryeae Pax, together with the genera Decarydendron Danguy, Ephippiandra Decne., Kibaropsis Veillard, Leviera Becc., Tambourissa Souner and Xymalos Baill. (3,4). The flowers of Hedycarya angustifolia are also notable for having a second whorl of the androecium (7).

In this paper we examine the leaf oils of the two endemic Australian species of Hedycarya as part of our ongoing analysis of the aromatic-leaved Australian rainforest flora, particularly those from families of ancient lineage such as the Monimiaceae (8,9).

Hedycarya angustifolia A.Cunn. (Fire-Stick Hedycarya or Native Mulberry) has an extensive range from King Island in the Bass Strait south of Victoria, up to the Conondale Ranges in southeastern Queensland (10,11). It is a shrub or small tree, generally up to 7 m high, but much taller plants (up to 20 m) have been recorded on rare occasions (10). The leaves are well known to be aromatic, viz. "tiny oil dots release a pleasant aromatic smell when the leaf is crushed" (11). Plants are found in wet sclerophyll forest dominated by eucalypts or in simple microphyll vineforest and moss-fern thickets (subtropical and temperate rainforests). In the recent past, the twigs of this plant were used as "twirling sticks" for fire-making by certain Australian aborigines (11) and for spear-ends (10).

Hedycarya loxocarya (Benth. ) W.D.Francis (Yellow Beech) is restricted to the "Wet Tropics" of northeastern Queensland with a northern limit at Shiptons Flat and a southern limit at Paluma (Queensland Herbarium (BRI) records). It is a small to medium sized tree up to 25 m high with "numerous small oil dots visible with lens" (12). Plants are found as understorey elements in wet sclerophyll forest dominated by eucalypts and casuarinas, or more commonly in complex notophyll vineforests (evergreen rainforests) on soils derived from metamorphic or granite rocks at altitudes from below 100 m up to 1100 m.

To the best of our knowledge, neither species ofHedycarya was used by indigenous Australians or the early settlers as bush medicine. However, the leaves of a New Zealand species, H. arborea J.R.Forst. et G.Forst. were used by the Maoris in vapor baths; the leaves of H. salomonensis have also been used medicinally (13). Alkaloids (14), (-)-5-exo-hydroxyborneol (15) and elemol (16) have been isolated from H. angustifolia. However, the latter has been shown to be an artefact arising from a thermally induced Cope rearrangement of hedycaryol (17). The current paper presents the first detailed analyses by GC/MS of the leaf oils of the Australian species of Hedycarya.