Joseph J Brophy*, Robert J Goldsack and Paul I Forster

Abstract: The leaf oils for species in the genus Bosistoa have been examined by GC and GC/MS. Bosistoa brassii produced a sesquiterpenoid leaf oil, the principal components of which were β−caryophyllene (2–12%), α−humulene (1–18%,) and bicyclogermacrene (trace – 24%). Bosistoa floydii produced a leaf oil (in poor yield) dominated by α−pinene (46–67%). The leaf oil of B. medicinalis contained significant amounts of α−pinene (13–57%). The principal sesquiterpene present in the oil was β−caryophyllene (1–9%). Bosistoa pentacocca, in both varieties, produced a leaf oil devoid of monoterpenes. The principal components in the leaf oil of this species were δ−cadinene (6-11%), α−copaene (2-7%), germacrene D (4–14%) and α−cadinol (2–8%). The leaf oils from B. transversa were variable, but the majority contained significant amounts of monoterpenes, with α−pinene (24–83%) being the principal component. The oil yields in all cases were poor (0.02–0.3%). Recommendations for taxon recognition in Bosistoa are made.

The genus Bosistoa F.Muell. ex Benth. is endemic to rainforest communities of eastern Australia and is classified in the Tribe Zanthoxyleae, subfamily Rutoideae of the Rutaceae. The genus was named for Joseph Bosisto (1827–1898), an English pharmacist, who discovered the antiseptic qualities of eucalyptus oil (1,2). A monograph of Bosistoa was published by Hartley in 1977 (3), who recognized seven species at that time, namely B. brassii T.G.Hartley, B. floydii T.G.Hartley, B. medicinalis (F.Muell.) T.G.Hartley, B. monostylis (F.M.Bailey) T.G.Hartley, B. pentacocca (F.Muell.) Baill, (with three varieties) and B. transversa J.F.Bailey et C.T.White. He later reduced the number of recognized species to only four, namely B. floydii, B. medicinalis , B. pentacocca and B. transversa (Hartley (4)). All species are small to medium sized trees, with opposite leaves that may be simple or variously compound. Hartley (3) placed the different species of Bosistoa in two groups based on the form of the bud scales and axillary buds. Bosistoa was considered most closely related to the monotypic Bouchardatia Baill., which is also endemic to eastern Australia (3). The genus probably also has close affinities to Acradenia Kippist, Dinosperma T.G.Hartley and Lunasia Blanco based on the shared character states of the endocarp being elastically discharged with the seed on fruit dehiscence, the seeds being pergamentaceous and lacking a sclerotesta, the endosperm lacking or greatly reduced and the straight embryo (4). These five genera were considered primitive and to have originated in Australia, with only Lunasia having radiated elsewhere (4). Populations of the different species of Bosistoa are relictual in their distribution and often highly disjunct in eastern Queensland and north-eastern New South Wales. In many cases they may be quite rarely encountered, although in general they are locally abundant where they do occur. At the time of Hartley’s (1977) revision, the genus was considered poorly collected, and some of the new species recognised at that time, e.g. B. brassii and B. selwynii were thought quite distinct on the available data. In the subsequent 20 years, many additional populations of Bosistoa have been found, and the subsequent collections have tended to produce morphological intermediates, hence the proposed reduction in taxa (4). A comparison of Hartley’s two systems is given in Table 1. For the purposes of this paper,the following taxa are recognized, viz. Bosistoa brassii (not recognized in Hartley (4)), B. floydii, B. medicinalis, B. pentacocca (with two varieties) and B. transversa. Bosistoa floydii T.G.Hartley is endemic to north-east New South Wales with a northern limit at the Upper Orara River and southern limit at Mistake Creek near Dorrigo. It is a small tree to 13 m tall and occurs in rocky situations along creeks in rainforest (complex notophyll vineforest), often on basalt. This is the most distinctive of all the species due to the imparipinnate foliage with 5–7-jugate leaves. Bosistoa brassii T.G.Hartley is endemic to north Queensland where it occurs in several disjunct centers of distribution. As originally defined by Hartley (3) it comprised two allopatric varieties, the type variety occurring on Cape York Peninsula (Iron Range, McIlwraith Range, Cape Melville) and the Wet Tropics; and the variety proserpinensis in the Mt Dryander and Conway Range area near Proserpine. Hartley (4) subsequently reduced B. brassii (including the varieties) to the synonymy of B. medicinalis. Populations named as B. brassii var. proserpinensis by Hartley (3) are referred here to B. medicinalis. Bosistoa medicinalis (F.Muell.) T.G.Hartley occurs in Queensland from the Proserpine area south to the Blackall Range. It is a small tree up to 15 m high and occurs in drier rainforests (araucarian microphyll to notophyll vineforests or complex notophyll vineforest), often in rocky situations along creeks on substrates derived from andesites, granites and granodiorites. Bosistoa pentacocca (F.Muell.) Baillon occurs in two varieties. B. pentacocca var. pentacocca is found from Ormeau in south-east Queensland south to the Big Scrub in north-east New South Wales. It is a small tree to 18 m tall and occurs in drier rainforests (complex to simple, microphyll to notophyll vineforests) on alluvium and colluvium derived from volcanic rock types. Bosistoa pentacocca var. connaricarpa is endemic to Queensland with three main centres of distribution, viz. Whitsundays – Conway Range – Eungella; Miriamvale district and near Mt Urah. It is also a small tree to around 18 m and occurs in similar rainforests, generally on andesites. Bosistoa transversa F.M.Bailey et C.T.White was considered by Hartley (3) to occur between Kin Kin in south-east Queensland and Mullimbimby in north-east New South Wales. With the later inclusion of B. selwynii T.G.Hartley into synonymy (4), the distribution of this species was extended north to west of Sarina. B. transversa is a small tree to 15 m tall and occurs in rainforest (semi-evergreen vinethicket, complex notophyll vineforest, araucarian microphyll vineforest) in rocky situations, often along creeks on substrates derived from andesites and basalts. There is no previously published work on essential oils from Bosistoa, however, Mueller (5), when naming Pagetia medicinalis (now Bosistoa medicinalis), noted that the oil from the leaves of this species had been used therapeutically. Triterpenes have been isolated from the leaves of B. pentacocca var. connaricarpa (under the illegitimate name B. sapindiformis F.Muell. ex Benth.) (6). A number of triterpenes and flavonoids have been isolated from the leaves of B. medicinalis by Parsons et al. (7) and a xanthine alkaloid and flavonoids from the leaves of B. floydii (8), while acridone alkaloids have been found in B. transversa leaves (9), and prenylated acetophenones were isolated from the leaves of B. transversa (as B. selwynii) (10). The triterpene, bosistoin, described by Croft et al. (11) was isolated from Acradenia euodiiformis (F.Muell.) T.G.Hartley, which was at that stage still included in Bosistoa as B. euodiiformis F.Muell. Phloroglucinol derivatives have also been isolated from the leaves of B. pentacocca (12). A review of the leaf chemistry has also been published (13). In the current paper, we describe the essential oils found in the leaves of Bosistoa with sampling undertaken throughout the genus. An attempt is made to see whether any differences in oil composition reflect either Hartley’s 1977 grouping of the species into two groups (3), or his subsequent reduction of the number of taxa recognized (4). As we have previously described the essential oil from the putatively allied genera Acradenia, Bouchardatia, Dinosperma and Lunasia (14–19), comparisons are also made to those taxa.