By Joseph J. Brophy, Robert J. Goldsack, Paul I. Forster, Lachlan M. Copeland, Wayne O’Sullivan, Andrew C. Rozefelds

Abstract: Abstract: The leaf oils of the 18 species and four subspecies of the genus Callitris endemic to Australia have been investigated by a combination of GC and GC/MS. All taxa produced oils in poor to moderate yields. Callitris baileyi produced a leaf oil in which α-pinene and limonene together, contributed the majority of the oil, while in Callitris canescens methyl citronellate also made significant contributions to the oil. In C. columellaris, limonene was the principal component, contributing up to 78% of the oil. Callitris drummondii gave a leaf oil which showed two chemical varieties. The samples from Western Australia contained large amounts of α-pinene (67–69%), while the sample from South Australia contained limonene (10.9%), bornyl acetate (24.2%) and geranyl acetate (14.9%) as significant components. In C. endlicheri the main components were limonene, α-pinene and bornyl acetate. Limonene and α-pinene were the principal components of the leaf oil of C. glaucophylla. Callitris gracilis ssp. gracilis gave an oil in which the principal components were α-pinene, myrcene and limonene, while in ssp. murrayensis α-pinene was the principal component. α-Pinene and limonene were the principal components of C. intratropica and C. macleayana. Callitris muelleri was found in two chemical forms, one monoterpenoid and one sesquiterpenoid, with either α-pinene or spathulenol being the principal component. In C. oblonga, which consists of three subspecies, α-pinene was the main component. In C. preissii the major components were α-pinene, myrcene, limonene and bornyl acetate. Callitris rhomboidea was distinguished from the vast majority of other Callitris species by containing significant amounts of neryl acetate, geranyl acetate and citronellyl acetate. Callitris roei contained significant amounts of sesquiterpenes in its leaf oil, with (E)-nerolidol being the principal component. In C. tuberculata α-pinene and limonene were the major components. α-Pinene, limonene and camphor were the major components in the leaf oil of C. verrucosa, while in Callitris sp. (Emerald Falls P.I. Forster +PIF26357) α-pinene and limonene were the principal components with significant amounts of α-fenchyl acetate. The leaf oil of the putative introgressed populations of C. columellaris – C. verrucosa had α-pinene (25–46%), myrcene (9–19%), limonene (14–24%), α-fenchyl acetate (8–13%) and bornyl acetate (4–13%) as the most significant components. The oil does provide similarities to the oils of both putative parent species in that it contains camphor (1–3%), which is characteristic of C. verrucosa and bornyl acetate (2–13%) characteristic of C. glaucophylla. Key Word Index: Callitris baileyi, C. canescens, C. columellaris, C. drummondii, C. endlicheri, C. glaucophylla, C. gracilis ssp. gracilis, C. gracilis ssp. murrayana, C. intratropica, C. macleayana, C. monticola, C. muelleri, C. oblonga, C. oblonga ssp. corangensis, C. oblonga ssp. parva, C. preissii, C. rhomboidea, C. roei, C. sp. (Emerald Falls P.I. Forster + PIF26357), C. tuberculata, C. verrucosa, Cupressaceae, essential oil composition, α-pinene, limonene, bornyl acetate, myrcene, methyl citronellate, geranyl acetate, α-fenchyl acetate, germacrene D, spathulenol, (E,E)-farnesol, neryl acetate, camphor, citronellyl acetate, (E)-nerolidol.

Introduction
The genus Callitris Vent. in the family Cupressaceae contains 20 species. Eighteen of these are found in Australia with the remaining two endemic to New Caledonia. Analyses of molecular data from the matK and rbcL sequences suggest that Callitris is most closely related to the genera Diselma (one species in Tasmania, Australia), Neocallitropsis (one species in New Caledonia), Actinostrobus (Western Australia, three species) and Widdringtonia (three species in Africa) (1). The family Cupressaceae in Australia contains five genera of which Callitris is the most speciose (2).

The Australian species of Callitris occur throughout the continent, including the island state of Tasmania. Although the majority of species occur on the eastern seaboard, several species occur in the Northern Territory, Western Australia and South Australia (3,4). All Callitris species form trees, usually small in stature (2–15 m high), but in some cases (e.g. C. macleayana) up to 30 m high. Unlike other Australian conifers, species of Callitris have been successful in colonizing the arid interior of the continent and many species exhibit xeromorphic morphology in the foliage. Most species of this genus have small (approximately 2–3 mm long) leaves that are tightly appressed to the branchlets. Many species form monospecific (or almost so) stands of trees and impart a unique appearance to the landscapes in which they occur. A comprehensive review of Callitris biology has been provided by Bowman and Harris (5), and the brief species descriptions that follow are drawn mainly from Hill (4) with information on distribution from there and the HERBRECS database at the Queensland Herbarium (BRI).

Callitris baileyi C.T.White is a tree growing up to 18 m in height. It is a rare species known from sporadic occurrences in shallow, often clayey soils in rocky areas in the ranges of southern Queensland from a northern limit at Yarraman, south to the tablelands of northeastern New South Wales (4).

Callitris canescens (Parl.) S.T. Blake is a small tree or shrub, growing to 6 m in height. It has been found from Kellerberrin to Southern Cross and south to Ravensthorpe, southwestern Western Australia and in the Eyre and York Peninsulas of South Australia (4).

Callitris columellaris F. Muell. is a tall erect tree, growing to 30 m in height. It is locally abundant in coastal areas of southeastern Queensland from Deepwater south to Angourie in northeastern New South Wales (4).

Callitris drummondii (Parl.) F. Muell. is a shrub to small tree, growing up to 10 m in height. It is a rare species occurring sporadically from Albany to Israelite Bay in southwestern Western Australia (4).

Callitris endlicheri (Parl.) F.M. Bailey (black cypress) is a tree growing up to 20 m in height. It is a widespread species occurring from Hinchinbrook Island in tropical Queensland, through the western slopes of New South Wales into eastern Victoria near the Ovens River (4).

Callitris glaucophylla J. Thompson et L.A.S. Johnson (white cypress or white pine) is a tall tree, growing up to 20 m in height. It is widespread and abundant across inland mainland Australia south of Mt. Garnet in Queensland usually on sandy soils where it may form monospecific stands (4). Populations of introgressed ‘hybrid swarms’ of this species and C. verrucosa occur on the southern Darling Downs in Queensland and adjacent parts of northern New South Wales. C. glaucophylla is extensively harvested and managed for timber production with the wood highly valued for its resistance to termite damage. Resin from this species has been used as a substitute for sandarac resin in the production of varnishes (6).

Callitris gracilis R.T. Baker is a tall tree growing up to 20 m in height. There are two subspecies, C. gracilis ssp. gracilis which occurs in southeastern South Australia, mainly in subcoastal regions, and C. gracilis ssp. murrayensis (J. Garden) K.D. Hill, which is abundant along the alluvial flats of the Murray River in New South Wales, Victoria and South Australia and extending west to the Flinders and Mt Lofty Ranges and the central Eyre Peninsular. In this latter region it intergrades with ssp. gracilis (4).

Callitris intratropica R.T.Baker et H.G. Sm. is a tall tree, growing up to 30 m in height. It is locally abundant in northern tropical Western Australia, Northern Territory and Queensland and grows in diverse habitats ranging from ‘dry’ rainforests (vineforest) to open woodlands (4). It has been grown in managed plantations on Melville Island in the Northern Territory with the wood prized for building.

Callitris macleayana (F. Muell.) F. Muell. (stringybark pine) is a tall tree that grows up to 30 m in height. It is highly disjunct in distribution with populations in the ‘Wet Tropics’ of northeastern Queensland and a number of populations south from Mt. Tamborine in southeastern Queensland to Clarencetown, New South Wales. It grows in subcoastal rainforest and rainforest margins (4).

Callitris monticola J. Garden (steelhead) is a shrub growing up to 2.5 m in height. It is a rare species, known from a few sites in mountainous areas on the north coast and northern tablelands of New South Wales and the Border Ranges of southeastern Queensland (4).

Callitris muelleri (Parl.) F. Muell. is a shrub or small tree, growing up to 6 m in height. It is known from the central coast of New South Wales, from Glen Davis to Gosford, south to near Nowra and with a single record from Eden (4).

Callitris oblonga (Rich. et A. Rich) is a small tree, growing up to 5 m in height. Three subspecies are recognised from the northern and southern tablelands of New South Wales and Tasmania. Callitris oblonga ssp. oblonga occurs in northeastern Tasmania, often along creeks and rivers. The subspecies corangensis K.D. Hill occurs at a single site along the Corang River, near Nerriga, New South Wales. Callitris oblonga ssp. parva K.D. Hill is also a rare subspecies, having a localised distribution around swamps and creeks in the northeast of the northern tablelands of New South Wales (4).

Callitris preissii Miq. is a shrub or tall tree, growing up to 20 m in height. It is endemic to southwest Western Australia in a small area around Perth and on Rottnest Island (4).

Callitris rhomboidea R. Br. ex Rich. (Port Jackson pine) is a small tree, growing up to 15 m in height. It has a sporadic and disjunct distribution from the Blackdown Tableland, Queensland to eastern Tasmania and southeastern South Australia (4).

Callitris roei (Endl.) F. Muell. is a shrub or small tree, growing up to 5 m in height. It has a scattered and disjunct distribution through southwestern Western Australia, from near Bolgart to the Stirling Range and east to Mt. Ragged (4).

Callitris sp. (Emerald Falls P.I. Forster +PIF26357) is of uncertain taxonomic status. It was recently recognised as being distinct by Pye et al. (2) and is restricted to a small area in the ‘Wet Tropics’ of northeastern Queensland in an area east of Mareeba. Its closest relative would appear to be C. intratropica (2).

Callitris tuberculata R. Br. ex R.T. Baker et H.G. Sm. is a shrub or small tree, growing up to 8 m in height. It is a widespread species of red desert sand hills, sand plains and coastal dunes and headlands through the Goldfields and eastern parts of the southern wheat belt districts of Western Australia and extending some distance into the Great Victoria Desert (4).

Callitris verrucosa (A. Cunn. ex Endl.) F. Muell. is a shrub or small tree, growing up to 8 m in height. It is a widespread species of the red desert sand hills from western New South Wales and northern Victoria west through southeastern South Australia to the sand hill country north of the Nullabor Plain (4). Relictual hybrid swarms (‘phantom’ hybrids) between this species and C. glaucophylla are sporadic in southern Queensland and northern New South Wales (4).

Callitris endlicheri, C. glaucophylla and to a lesser extent C. macleayana and C. columellaris have all been used for timber production (7–10). Their woods are resistant to termites and other insects, no doubt because of the presence of sesquiterpene acids and lactones in the resinous materials as well as guaiol and callitrol giving it a resistance to fungal decay. Maiden, the New South Wales Government botanist, reported in 1917 that “It is one of the most luxurious fire woods I know of; it burns well, and in burning emits a delicious fragrance very generally admired. My idea is that the small pieces produced in sawmills would sell at a remunerative price, as a superior kind of fuel for drawing rooms etc. if people could only obtain it. This may appear to be only a trifling matter, but I think that minor uses of our timbers (and above all, utilisation of waste) should be looked at.” (10)

Over the last hundred years or so, a substantial number of chemical investigations have been carried out on Callitris. However, when reading the older chronicles, it needs to be borne in mind that many changes in species’ circumscriptions and nomenclature have occurred with time. In many instances, it is not possible to check the identity of material used because voucher details are lacking. In the work presented here, we use the nomenclature of the Flora of Australia (4).

Undoubtedly, the classic work on the essential oils of Callitris is that of Baker and Smith dating from almost a century ago (11). These pioneers examined the oils obtained from both leaves and wood, and although they succeeded in isolating and identifying a number of mono- and sesquiterpenes, their work was hampered by poor oil yields. Their work will be discussed in conjunction with our findings. Other classes of compounds isolated from Callitris include fatty acids (12,13), flavonoids (14,15), biflavonoids (16–18), terpenes (18–27,) and podophyllin (28–30).

By any standards, Callitris timbers are hard and dense and are renowned for their resistance to the depredations of Australia’s termite fauna. Consequently, Callitris timbers have been investigated for compounds possessing anti-termite activity.

Callitris essential oils applications include insecticides (31), antimicrobial compounds (32) and fragrances (33). The vast majority of published work on the genus Callitris has been on the extractives of the wood. We are aware of seven publications dealing with oils obtained from the leaves (11, 34–39); however, this paper is the first to document the oils from all the known Australian species.