Chemistry of the Australian Gymnosperms. Part 6. Leaf Oils of the Australian Species of Genus Podocarpus

Journal of Essential Oil Research: JEOR, Jul/Aug 2004 by Brophy, Joseph J, Goldsack, Robert J, Forster, Paul I, Rozefelds, Andrew C

Abstract

The leaf oils of the Australian members of the genus Podocarpus have been analyzed using GC and GC/MS. All species produced poor yields of oils (0.01-0.3%). The leaf oil of P. dispermus contained isopimara-9(11),15-diene (10.3%) and a C^sub 20^H^sub 32^ (B) compound (12.7%) as principal components. Bicyclogermacrene (57%) was the principal component of P. drouynianus. Podocarpus elatus gave an oil in which [alpha]-pinene, [beta]-caryophyllene and bicyclogermacrene were the principal components. Bicyclogermacrene (27-44%), germacrene D (4-11%) and spathulenol (3-11%) were the principal components of the oil from P. grayae. Podocarpus lawrencei was one of only two Australian Podocarpus species to produce an oil (0.1-0.6%), which contained significant amounts of diterpenes. The main components were [alpha]-pinene (14-18%), [beta]-caryophyllene (3-15%), spathulenol (0.8-19%), rimuene (0.2-30%), sandarocopimara-8(14), 15-diene (0.1-20%) and beyerene (7-9%). Podocarpus smithii produced a complex sesquiterpenic oil in which [alpha]-copaene (4-8%), [beta]-caryophyllene (5%) and [delta]-cadinene (9-11%) were the main components. Limonene (13-16%), bieyclogermacrene (15-18%) and viridiflorol (16-18%) were the main components of P. spinulosus oil.

Key Word Index

Podocarpus dispermus, Podocarpus drouynianus, Podocarpus elatus, Podocarpus grayae, Podocarpus lawrencei, Podocarpus smithii, Podocarpus spinulosus, Podocarpaceae, essential oil composition, [alpha]-pinene, limonene, sabinene, [beta]-caryophyllene, bicyclogermacrene, germacrene D, viridiflorol, spathulenol, isopimara-9(11),15-diene, rimuene, sandarocopimara-8(14),15-diene.

Introduction

The gymnospermous family, Podocarpaceae, is made up of 180 species that are unevenly distributed among about 18 genera (1). Of the latter, by far the largest is Podocarpus L. Her. ex Pers. containing some 106 species that are mainly distributed in the tropics and subtropics of the southern hemisphere (1,2). No comprehensive monograph exists forthe genus, with the account of de Laubenfels (2) being essentially synoptic in its coverage. Seven species, namely P. lawrencei Hook, f., P. smithii de Laub., P, grayae de Laub., P. dispermus C.T. White, P. spinulosus (Sm.) R.Br. ex Mirb., P. drouynianus F. Muell. and P. elatus R.Br. ex Endl. are endemic to Australia (1), although Hill (3) mentioned that the seventh species, f! elatus, occurs in New Guinea as well. Podocarpus spinulosus, P. lawrencei and P. drouynianus are shrubs whereas the remaining species grow into quite large trees. Podocarpussmithii,P. grayae,P. dispermus andf! elatus occurin moist tropical areas of eastern Australia, with the latter extending to the cooler parts of eastern New South Wales.

Podocarpus dispermus is endemic to the 'wet tropics' region of northeastern Queensland with a northern limit at Danbulla and southern limit at Gregory Falls near Innisfail. It forms a large canopy tree up to 30 m tall in wetter rainforests (complex notophyll or mesophyll vineforests) on diverse geological substrates (basalt, granite, metamorphics) at altitudes between 40 and 800 m.

Podocarpus drouynianus is found in the southwest of Western Australia where it occurs in the Jarrah forests as a component of heath shrubland (3) on sandy soils. The species is a small shrub up to 4 m tall.

Podocarpus elatus ('brown pine') is the most widespread species with a northern limit at Silver Plains Station in the Mcllwraith Range on Cape York Peninsula, Queensland and a southern limit south of Kiama in New South Wales. It grows as a small to large tree up to 30 m high in a variety of drier rainforest communities (araucarian microphyll or notophyll vineforests, littoral microphyll vineforest) from near sea level to around 920 m altitude on substrates derived from diverse geologies (basalt, granite, metamorphics).

Podocarpus grayae (sometimes incorrectly known as 'grayi) is a small to large tree up to 30 m tall. In eastern Australia it is widely distributed from the Torres Strait in the north, south to near Townsville, although the main area of distribution occurs from Iron Range south to just north of Cape Tribulation. There are also a couple of relict and highly disjunct populations in Arnhem Land in the Northern Territory. This species occurs in lowland rainforests (from near sea level to 700 m altitude) such as complex notophyll or mesophyll vineforests or semi-deciduous microphyll vineforest on diverse substrates such as alluvium or those derived from granite, sandstone or metamorphic geologies.

Podocarpus lawrencei ('mountain plum pine') is usually endemic to the subalpine and alpine region of southeastern Australia (Victoria, New South Wales, Australian Capital Territory) (3-5) but also occurs as a riparian shrub in eastern and northern Tasmania. The species typically grows as a small shrub up to 4 m tall on scree and steep slopes at altitudes between 1,440 and 2,100 m, but occasionally occurs at lower altitudes (about 400 m) on the Mersey and Douglas Rivers in Tasmania (6).