Leaf Essential Oils of the Queensland Species of Phebalium (Rutaceae: Boronieae)

Journal of Essential Oil Research: JEOR, Jul/Aug 2006 by Brophy, Joseph, Goldsack, Robert, Forster, Paul

Abstract

The leaf oils of the eight Queensland specific and subspecific taxa of Phebalium have been examined. Phebalium distans produced a variable oil, with α-pinene (0.8-42%) being the most abundant prominent monoterpene and bicyclogermacrene (12-22%) as the most significant sesquiterpene. In P. glandulosum subsp. glandulosum by far the major component is dihydrotagetone (75-95%). β-Caryophyllene (9-20%) and bicyclogermacrene (7-23%) were the major components of P. longifolium. In P, nottii the principal monoterpene detected was α-pinene (25-42%), while the principal sesquiterpenes detected were guaiol (t-28%) and bulnesol (nil to 34%). The two monoterpene hydrocarbons, α-phellandrene (12-25%) and β-phellandrene (14-15%), togetherwith bicyclogermacrene (2-12%), elemol/hedycaryol (12-36%) were major components in the leaf oil of P. squamulosum subsp. squamulosum, while in P. squamulosum subsp. gracile, geijerene (4-8%) was present together with α-pinene (44-50%) and guaiol (9-11%). The leaf oil of P. whitei contained α-pinene (22-42%), limonene (1-12%) and bicyclogermacrene (11-20%) as major components. In P. woombye the main components were α-pinene (10-21%), β-phellandrene (12-20%), bicyclogermacrene (11-20%) and germacrene D (5-10%).

Key Word Index

Phebalium disions, Phebalium glandulosum subsp. glandulosum, Phebalium longifolium, Phebalium nottii, Phebalium squamulosum subsp. squamulosum, Phebalium squamulosum subsp. gracile, Phebalium whitei, Phebalium woombye, Rutaceae, essential oil composition, α-pinene, α-phellandrene, β-phellandrene, elemol, hedycaryol, bicyclogermacrene, β-caryophyllene, limonene, guaiol, bulnesol, dihydrotagetone.

Introduction

The genus Phebalium Vent. (Rutaceae) currently contains approximately 26 species, all endemic to Australia (1,2). Many species that were formerly included in Phebalium are now classified in the genera Leionema (F.Muell.) Paul G. Wilson, Nematolepis Turcz. and Philotheca Rudge with Phebalium thought to be most closely allied to the genus Microcybe Turcz. (1). The so-called Phebalium group of genera in the Boronieae contains Chorilaena Endl., Leionema, Microcybe Turcz., Nematolepis, Phebalium and Rhadinothamnus Paul G. Wilson (1).

Species of Phebalium are found in two main centres of distribution, eastern mainland Australia and Tasmania, and southwest Western Australia. The different species range from being mainly small woody shrubs or subshrubs to one species (P. distorts P.I.Forst.) that forms a small tree (2). A number of species have colourful flowers (e.g. P. nottii, P. whitei) and there is limited use in horticulture for a number of species as ornamentals or for cut flowers (3). All species have foliage that is aromatic when crushed and some species (e.g. P. glandulosum) have distinctive glandular foliage that is beset with raised tuberculate glands.

As a consequence of the large number of changes in the nomenclature oiPhebalium s.l., the chemical literature needs to be interpreted in conjunction with the taxonomic works of Wason(1,4)and(2).

A large number of extractives have been isolated from Phebalium s.l., including coumarins (5-8) andaprotolimonoid (9). In addition, mono- and sesquiterpenoids have been reported for a number of species: myrtenyl acetate (10), spathulenol, ( )-4-β, 10-α-dihydroxvaromadendrane and ledol (11) from P. megaphyllum (Ewart) Paul G. Wilson (syn. P. tuberculosum (F. Muell.) Benth. subsp. megaphyllum (Ewart) Paul G. Wilson), isomurralonginol isovalerate (12), spathulenol and ( )-4-β, 10-α - dihydroxyaromadendrane (11) from P.filifolium, ( ) 2,6-dimethyloct-7- en-4-one (dihydrotagetone) from P. glandulosum subsp. gllandulosum (13), squamulosone, a sesquiterpene ketone, from P. squamulosum (subsp. not specified) (14), and d-pinene, myrcene, α- and β-eudesmol and elemol/hedycaryol from P. stjuamulosum subsp. ozothamnoides (syn. P. ozothamnoides) (15).

In the current paperwe present analyses of the leaf essential oils of the eight taxa of Phehalium that occur in the state of Queensland. A ninth taxon, P. glandulosum subsp. eglandulosum has been recorded from a single locality at Passchendale near Stanthorpe (16) but was last seen in 1977 when the population consisted of a single plant (W.McDonald, pers. comm. July 2003). Efforts to relocate this plant in Queensland have been unsuccessful and it is not included in the current analyses. Brief descriptive notes are provided here on the eight taxa known to be extant in Queensland.

Phehalium distans P.I.Forst. This newly described species (2) is endemic to southeastern Queensland where it has a restricted distribution from Mt Walla in the north (25° 38'S) to Mt Berryman, near Laidley in the south (27° 43'S). It is unique in the genus Phehalium for the tree habit to 8 m tall, although it also occurs as a shrub. Plants grow in the midstorey and canopy of semi-evergreen vine thickets on red soils derived from basalt.

Phehaliumglandulosum Hook. (Desert Phebalium). Four subspecies are currently recognized (1). Only Phehalium glandulosum subsp. glandulosum is common in Queensland. P. glandulosum subsp. eglandulosum Paul G. Wilson has been recorded twice from Queensland but is now thought to be extinct; otherwise this subspecies is found in northern New South Wales. The other subspecies of this species, P. glandulosum subsp. anpustifolium Paul G. Wilson and P. ftlandulosum subsp. nitidum, are both endemic to central New South Wales (1). Phehalium glandulosum subsp. glandulosum is one of the most widespread taxa of Phehalium with a northern limit at Fredericks Peak near Townsville in Queensland (19° 23'S) to the Snowy River in Victoria in the south (37° 16'S). This subspecies grows in heathland or open woodland in rocky situations on a variety of substrates (basalt, latente, rhyolite, sandstone, trachyte). It forms a small shrub to 1.5 m high and has yellow flowers.