Their botany, essential oils and uses
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- Figure 9.
- Figure 15.
Figure 10. Melaleuca endemism. The greatest endemism occurs in the south-central coastal region of Western Australia with some moderately strong areas of endemism in the north-western part of the south-west. There are some lesser areas of endemism in eastern Australia.
0 740 1,480 2,220
2,960 Kilometres Species richness High : 72
Low : 1
N 0 740 1,480 2,220
2,960 Kilometres N Endemism High : 9.92035
Low : 0.00518135 29 2. I
ntr oduction to the genus Melaleuc a Fenton et al. 1977), particularly in South-East Asia and USA, can be ascribed to M. cajuputi and M. quinquen- ervia and not M. leucadendra. Most current interest in the species for plantation establishment is in the Mekong Delta of Vietnam, where M. leucadendra outperforms the indigenous M. cajuputi subsp. cumingiana on season- ally inundated and potentially acid-sulfate sites which are very difficult for tree establishment (Hoang Chuong et al. 1996). Melaleuca alternifolia is planted for the production of essential oil in Australia—3,000 ha producing 450–500 tonnes (t) of essential oil/year—but the total area planted and the total production worldwide is potentially twice this from plantings outside Australia in several countries, including China. Broombush (M. uncinata complex) plantings in Australia for brushwood fencing and related products exceed 1,000 ha. There are extensive, but largely undocumented, plant- ings of melaleucas as ornamentals, street and public park trees, shelterbelts on farms and for land reclamation in Australia and elsewhere. Tolerance of difficult conditions As well as being tolerant of periodic (Figure 12) or even continuous waterlogging, many of the wetland melaleucas will also survive and grow in moderately to highly saline soils (e.g. M. armillaris, M. bracteata, M. cuticularis, M. decussata, M. ericifolia, M. lanceolata, M. lateriflora, M. leucadendra, M. linariifolia, M. quinquen- ervia, M. squarrosa, M styphelioides and the M. uncinata
south-western Western Australia (WA); (C) shrubby M. sophisma under an overstorey of mallet in south- western WA; and (D) trees of M. cuticularis on the edge of a wet, possibly saline area in south-western WA
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ntr oduction to the genus Melaleuc a complex). A few melaleucas are tolerant of extremely saline conditions (e.g. M. halmaturorum and M. thyoides). Many of these same species are also tolerant of alkaline soils, drought and frost (Marcar et al. 1995; Marcar and Crawford 2004). Melaleucas appear to employ a diverse range of physiological strategies to adapt to difficult growing conditions. For example, Naidu et al. (2000) found that species with the capacity to accumulate one or, prefer- ably, more of the methyl prolines in their leaves were better adapted to saline and/or sodic soils than species that accumulated only L-proline. This was the case with M. cuticularis: Carter et al. (2006) found that the ability of this species to tolerate saline-waterlogged conditions was related to production of methyl proline, as well as regulation of foliar sodium, chloride and potassium concentrations. Ionic stress and the differential ability of seedlings of M. leucadendra provenances to adjust for a declining potassium concentration in leaf sap under com- bined salt and aluminium stress was thought to be the main cause of variation in growth of 16 M. leucadendra provenances in a glasshouse trial (Nguyen et al. 2009). Mensforth and Walker (1996) found that the root dynam- ics of M. halmaturorum in response to fluctuating saline groundwater contributed to the survival of this species in saline swamps. Melaleuca halmaturorum accessed water from deep in the profile in late summer when salt had accumulated in the surface soils and used rainfall and shallower groundwater after winter rains had replenished the profile. The ability of this species to take up water from saline substrates through maintenance of low leaf water potentials was also a contributing factor (Mensforth and Walker 1996). Some wetland melaleucas, like the tropical M. leuca- dendra group, develop aerial adventitious roots on their stems and within the papery bark to the height of the maximum water level during flooding (Figure 13). These are dense in aerenchyma cells which have large intracel- lular air spaces that improve internal root aeration and gas exchange during inundation. The fine adventitious roots on the stems of M. quinquenervia in a seasonally inundated forest in northern Queensland, for example, were considered an important part of the reason that tran- spiration in this species was unaffected by inundation of up to 24 weeks (McJannet 2008). In M. cuticularis, they appear to contribute to this species’ enhanced tolerance to combined salinity and waterlogging (Carter et al. 2006). Tanaka et al. (2011) reported that seedlings of M. cajuputi in the tropical peat swamps of southern Thailand were able not only to survive complete submergence for 8 weeks but also to photosynthesise and grow during this period. This was due to the strong development in the leaves and stems of submerged seedlings of schizogenously formed aerenchyma which improved uptake of gases from the water.
Many melaleucas are highly fire-tolerant during all but the early seedling stages before a thick protective layer of bark has formed. Fire-ravaged individuals regenerate through stimulation of epicormic buds under the thick bark to sprout vigorously after fire in a process called coppicing (Figure 14). Populations may expand through fire-induced release of seed from serotinous capsules on the trees and stimulation of germination of seed in soil seedbanks. Some melaleuca species have the ability to root sucker, and through root extension and interconnectivity form
Vietnam: (A) a young planting as the inundation recedes; and (B) a dense plantation nearing rotation age A B 2. I ntr
oduction to the genus Melaleuc a 31 dense clumps of single clones. This is a common adaptive characteristic of wetland plants subject to very difficult conditions for survival, growth and sexual recruitment (see review in Robinson et al. 2012). Using DNA markers, Robinson et al. (2012) showed that the large, dome-shape stands of M. ericifolia in Dowd Morass, Gippsland Lakes, Victoria, were individual clones that did not intermin- gle (phalanx growth habit) with adjacent clones. They speculate that this is also the case with other stands of this species in southern Australia. Melaleuca viridiflora also forms root suckers. Crowley et al. (2009) showed that population density of this species increased dramatically in grasslands and grassy woodlands in northern Queens- land in the absence of fire by recruitment of suckers to the sapling layer. Figure 13. Aerial adventitious roots on the stems of: (A) Melaleuca quinquenervia growing naturally in a seasonal swamp beside the Bensbach River, Western Province, Papua New Guinea; and (B) M. leucadendra planted in the Mekong Delta, Vietnam
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oduction to the genus Melaleuc a 32
33 Ethnobotanical Some Melaleuca species were used extensively by the Aboriginal peoples of Australia for a wide variety of cultural uses (refer to Williams 2011 for a description of 17 species used by Aboriginal communities). The papery bark of several, mainly tropical, melaleucas (e.g. M. argentea, M. dealbata, M. cajuputi, M. leucadendra and M. viridiflora) had many domestic uses, including water-repellent roofing material, raft-making, in food preparation, bandages, blankets, baby slings, body wraps in burial ceremonies and for dresses denoting marriage, to name but a few (Levitt 1981; Wrigley and Fagg 1993; Yunupingu et al. 1995; Blake et al. 1998; Puruntatameri et al. 2001; Wiynjorrotj et al. 2005; Williams 2011; Wiersema and León 2013). The leaves of species such as M. acacioides, M. argentea and M. leuca- dendra were used as flavouring in cooking and M. argentea leaves were burnt to repel mosquitoes. The trunks of some species (e.g. M. cajuputi, M. leucadendra and M. viridi- flora) were used for construction of canoes and shields. ‘Bee bread’ (produced from pollen) and honey were foods collected from native bee hives prevalent in Melaleuca swamp forests of M. acacioides, M. lasiandra, M. leuca- dendra, M. minutifolia, M. nervosa and M. viridiflora in northern Australia (Williams 2011). Williams (2011) also notes reports of early explorers (e.g. Leichhardt in 1847 and Mitchell in 1848) in northern Australia of the col- lection by Aboriginal peoples of melaleuca honey and melaleuca flowers (e.g. from M. saligna). The latter were soaked in water to produce a sweet-tasting drink. Melaleucas were an important source of dry-season water for the nomadic Aboriginal peoples (and early European explorers), particularly in the wet/dry tropics of northern Australia. Bulges in the trunks of individual trees of such species as M. argentea, M. cajuputi, M. deal- bata, M. nervosa and M. viridiflora when undercut could yield about a litre of brackish but nevertheless potable water (Yunupingu et al. 1995; Puruntatameri et al. 2001; Wiynjorrotj et al. 2005; Williams 2011). Melaleucas played an important role in traditional Abor iginal medicines. The leaves and inner bark of M. argentea and others like M. cajuputi and M. leucaden- dra were used medicinally (coughs and colds, aches and pains, cuts and sores, ringworm, vomiting and diarrhoea and other malaises), either directly following crushing or burning (smoking medicine) and inhaling the odours or as
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ses a liniment or drink after soaking the leaves or inner bark in water and heating (Blake 1968; Levitt 1981; Aboriginal Communities of the Northern Territory 1993; Wrigley and Fagg 1993; Yunupingu et al. 1995; Puruntatameri et al. 2001; Wiynjorrotj et al. 2005; Lassak and McCarthy 2011; Williams 2011). The bark of some melaleucas was used as a poultice on wounds and for splinting broken bones, where the juice of the bark was said to penetrate the skin and aid in healing (Williams 2011). The milky extract of squashed ‘bee brood’ (bee pupae and larvae) collected from native beehives prevalent in melaleuca swamp forests was used as a topical antiseptic for sores, tinea and eye complaints (Williams 2011). Ornamental, landcare, honey, bark and wood Ornamental and amenity–horticultural use Melaleuca species, especially the bottlebrushes, have long been popular garden subjects in Australia. The first Austral- ian melaleucas to be cultivated, however, were grown in Europe, presumably from seed taken to England in 1771 by Joseph Banks. Melaleuca armillaris, M. decora, M. erici- folia, M. hypericifolia, M. nodosa, M. styphelioides and M. thymifolia were in cultivation by 1793 (Elliot and Jones 1993; Wrigley and Fagg 1993). Seed and/or transplants of the bottlebrush species M. citrina and M. linearis also were taken to Europe in the late 1700s and these species rapidly became popular conservatory plants. Melaleuca citrina was in fact named and described (as Metrosideros citrina) in 1794 from material cultivated in England and M. linearis was described in 1796 from material cultivated in Germany. Many species (including cultivars derived from selec- tion or from interspecific hybrids) are hardy in cultivation in Australia (Elliot and Jones 1982, as Callistemon; Elliot and Jones 1993; Wrigley and Fagg 1993, also as Callis- temon; Holliday 2004; Stewart 2012, also as Callistemon). Some tolerate moderate levels of frost and others grow well in poorly drained soils. Because there are species of diverse habit, flower form and colour, and substrate preference in most of the major climatic zones within Australia, it is possible to select a species for a specific purpose, e.g. for a hedge, windbreak, specimen shrub or tree. Several species have particularly attractive papery bark and are worth cultivating for this feature. Several of the larger shrub and tree species are ideal for amenity plantings as street trees, screens for industrial sites, highway verges and so on. Many of the tree species are ideal for use in parks and large-scale landscape applications. The trees that have colourful, nectariferous flowers (Figure 15) usually attract nectar-feeding birds if these occur in the region. There are surprisingly few melaleuca cultivars available in the horticultural industry in Australia and most, if not all, of these are selections of species. The bottlebrushes are an exception. Barriers to successful hybridisation between certain species apparently do not exist and, when grown in a common garden, bird- or insect-mediated hybridisation has resulted in the occurrence of hybrid plants. In many cases, selections have been named and propagated com- mercially. The following species (as Callistemon) have been recorded as being a parent, or putatively a parent, of named cultivars: M. citrina, M. comboynensis, M. glauca, M. pachy- phylla, M. phoenicea, M. polandii (doubtfully this species and more likely to have been M. hemisticta or M. pyrami- dalis), M. recurva, M. salicina, M. subulata and M. viminalis (Elliot and Jones 1982; Wrigley and Fagg 1993). Much more
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35 work needs to be done as far as bottlebrush breeding is concerned. There is considerable opportunity for breeders to select growth and colour forms of species and cross them with an aim of obtaining a particular combination of char- acters. The two broad climatic zones that should be targeted for such hybridising endeavours are the tropical–subtropi- cal and subtemperate zones in Australia and elsewhere. As to other species groups within the genus, it seems there have been no hybridisation programs. The field is open for such programs to be initiated. The pom-pom- flowered M. scabra group is an obvious candidate as there is much variation within this group that could be bred into novel, improved garden plants. Although many of the spe- cies of the M. scabra group occur on leached, sandy soils, some of them occur on clay soils and these species may confer some degree of soil adaptability to hybrids. Mela- leuca nesophila, an M. scabra group species of restricted range and habitat in the high rainfall, coastal part of south- western Western Australia, is remarkably hardy and grows well on heavier soils in the dry Western Slopes region of New South Wales. Using species such as M. carrii, M. fabri, M. hamata, M. nematophylla, M. nesophila, M. oldfieldii, M. sapientes and M. systena—and there are many oth- ers—it may be possible to develop hybrids of merit for Mediterranean and dry-temperate climates. Another group with potential as garden plants is the M. fulgens group, and a hybridisation program involv- ing such species as M. coccinea, M. elliptica, M. eximia, M. fulgens, M. lateritia and M. macronychia may result in a series of red- to orange-red-flowered, bushy plants to rival the bottlebrushes, as the species of the M. fulgens group also have bottlebrush inflorescences. Naturally occurring hybridisation in Melaleuca has been reported from a wide range of species (Craven 2006, p. 470) and it seems barriers to hybridisation within a species group or species complex are not absolute; in fact, where two or more species of the same group occur in biotic sympatry, hybridisation may be frequent. An interesting application is the use of melaleucas as bonsai (known as penjing in China and cay canh in Viet- nam). Bark texture, small leaves and flowering propensity are some of the criteria by which species are rated. Over 60 species, varieties and cultivars of Melaleuca have been recorded by the Australian Plants as Bonsai Study Group as being grown in bonsai within Australia (Roger Hnatiuk, pers. comm.). Early use of melaleucas tended to mimic the styling of classic Japanese trees but in recent years bonsai artists are exploring the beauty of branches and crowns of old mature trees of the species found growing in nature. Bonsai, inspired by such forms, are beginning to be seen in public displays (Figure 16). Notes on species of particular, or potential, value for ornamental and amenity–horticultural use are provided in the ‘Species accounts’ (Chapter 7). The main impediment to their wider use within Australia and elsewhere is the difficulty in obtaining planting material of superior colour and growth forms of the species, or forms from particular soil types.
western Western Australia; and (B) M. bracteata, usually a medium-size tree up to 22 m tall from inland and coastal northern Australia
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36 Land rehabilitation Melaleuca comprises many species of trees and shrubs that are hardy and adaptable to a wide range of habitats and soils. They regularly occupy sites that are very challeng- ing for tree survival and growth (Figure 17), as discussed in other sections of this volume. Their diversity in form, adaptability and utility sees them listed prominently among candidate species for planting for land reclama- tion, with natural resource benefits including mitigation of salinity, waterlogging, and water and wind erosion. Biodiversity improvements, carbon sequestration and potential to increase farm income (e.g. through produc- tion of brushwood fencing, essential oils and bioenergy) are among other commonly stated benefits of planting melaleucas on degraded lands. Highly topical at present is the increasing problem of saline landscapes in Australia and elsewhere. There are over 4 million ha of secondary or human-induced saline soils in Australia, in addition to 29 million ha of naturally Figure 17. Salt-tolerant melaleucas: (A) Melaleuca halmaturorum on a saline site in southern Australia; and (B) M. atroviridis surviving on the margin of an area severely affected by secondary salinity in south-western Western Australia
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ses occurring salt-affected lands (Marcar and Crawford 2004). The removal of native vegetation and development of annual agricultural systems in southern Australia, leading to ris- ing watertables carrying soil-borne salt to the surface, are major contributors to salinisation of landscapes. Restoration of deep-rooted perennial vegetation can make a significant contribution to correcting this problem but it needs to be on a large scale to control salinity (Pannell and Ewing 2004). A range of Melaleuca species is suitably adapted to grow on saline sites (e.g. Figure 17), ranging from moderately (4–8 dS/m ECe) to extremely saline (>16 dS/m ECe) (Mar- car et al. 1995; Department of Agriculture and Food Western Australia 2004; Marcar and Crawford 2004). Melaleuca halmaturorum is an example of a temperate Melaleuca tree/shrub adapted to extremely saline condi- tions, while M. leucadendra is among the tropical tree-form melaleucas adapted to highly saline conditions. Both spe- cies are tolerant of waterlogging. Unfortunately, few of the presently recognised salt-tolerant melaleucas offer scope to growers for direct financial benefits, thus large-scale planting is not attractive. Melaleuca uncinata, one of the source species for brushwood (see below), and its relative M. atroviridis, are two exceptions. Melaleuca bracteata might have potential in the future if an industry were to develop around the production of betaines from its foliage. Brushwood fencing and related products Ornamental brushwood fencing comprising the grey stems, twigs and dry foliage of the M. uncinata complex of species (broombushes), hand-packed on wires in situ or, in more recent times, prefabricated in panels, has been in use in Australia for more than 80 years (McKelvie et al. 1994) (Figure 18). It represents an important market for melaleucas, despite its small size compared with alterna- tive fencing materials (e.g. 1% of the fencing market in Western Australia). Other uses of brushwood include manufacture of garden furniture, gazebos, pergolas, gates, hanging baskets and decorative bird feeders (Robinson and Emmott, no date). McKelvie et al. (1994) indicated that about 600,000 bundles of brushwood (each c. 25 kg, consisting of stems with foliage of 1.4–1.8 m in length and 7–15 mm in diameter) were used in Australia each year, with predicted annual market growth of 5.5%. Melaleuca uncinata is the most common broombush used for brushwood fencing. It is widespread in southern Australia, mainly south of the Tropic of Capricorn. Mela- leuca uncinata is a hardy, bushy shrub to 7 m in height with multiple long, thin, woody erect stems topped with foliage (broom-like). It is adapted to a wide diversity of habitats and soils, mainly in semi-arid and arid Australia (see range given in its species description). Other broombushes in the M. uncinata complex having potential for brushwood fenc- ing are the Western Australian endemics M. atroviridis, M. concreta, M. hamata and M. osullivanii (Robinson and Emmott, no date). Melaleuca acuminata and M. hamulosa are also worth trialling as alternative species as they have similar physical characteristics to the traditionally used M. uncinata (Peter White, pers. comm. 2012). Until recent times, all harvesting of brushwood has been in native stands and producers are licensed by the various state governments. Overall, 50–70% of plants are harvested manually of which 90% can be expected to cop- pice in a typical bush operation based on a broombush population of about 3,000 plants/ha. This yields between 3–6 t product/ ha. The interval between harvests is 10–14 years (Wrigley and Fagg 1993). Concerns about adverse environmental effects have seen the gradual withdrawal of public lands from resources available for harvesting and concerns have arisen about the sustainability of brushwood supply from native stands. The likely direct economic ben- efits, complemented by the indirect benefits of establishing broombush on private lands for purposes such as shelter, salinity control, soil erosion control, biodiversity and diversification of farm income, have led to interest among some landholders in the drier regions of the southern states in developing commercial plantations of broombush. It is estimated that a total plantation area in the order of 2,000–2,500 ha would be required to fully meet demand on a sustainable basis (Cameron 2003; AVONGRO 2007). The total area planted is not known but about 900 ha had been planted in the Avon catchment area of Western Australia alone by 2007 (AVONGRO 2007). Various landcare agencies in Western Australia, South Australia and Victoria have published informative ‘fact sheets’ on growing broombush by either direct seeding or planting tube stock and readers interested in this topic are directed to these for detailed information (e.g. Bulman et al. 1998; Cameron 2003; Robinson and Emmott, no date). Until recently, broombush was regarded as being a single species, M. uncinata. It is now known that there are several species involved (Craven et al. 2004), a number of which are suitable for brushwood production as mentioned above. Honey Most melaleucas do not provide major honey crops. Clem- son (1985), however, pointed out that many species assist indirectly with honey production by providing nectar and pollen, especially nectar, in sufficient quantities to stimu- late brood-rearing and sometimes for use as stores. In this way, colonies are maintained and built up for subsequent major honey flows in other taxa. Those which are important honey producers include the broad-leaved melaleucas. Melaleuca quinquenervia is a major source of honey in Australia and Florida (Blake and Roff 1972; Robinson 1981; Clemson 1985; Geary 1988) and similarly M. cajuputi in northern Australia and Viet- nam (Brock 1988; Mulder 1992). Melaleuca leucadendra is also said to be an important source of honey in its area
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38 of natural occurrence (Roff 1966; Anderson 1993). The honeys from these species are variously described as light to dark amber in colour, with strong flavour and odour and of low density so they granulate readily. Their pollens are universally described as being a good source of protein utilised by bees in building up colonies. Bark
The bark of Melaleuca species is still used today in the con- struction of traditional houses in Papua New Guinea. It is used to line fernery baskets, for making bark paintings and the cork from the bark has been used in infants’ pillows and mattresses (Bootle 1983). The bark of M. cajuputi is used in parts of Malaysia as a luting material in boatbuild- ing (Lum 1994; Lim and Midon 2001). Wood
Fuelwood There is little reported on the fuelwood value of individual species in the genus Melaleuca. Apart from the state- ment in Maiden (1889) that M. linariifolia wood made Figure 18. Facets of the brushwood fencing industry: (A) the multistemmed habit of species in the broombush complex (this is Melaleuca stereophloia); (B) a native broombush (M. uncinata) population; (C) broombush bundles in the field ready for transport; (D) transporting the bundles to market; (E) constructing a brushwood fence in situ; and (F) a typical brushwood fence A C E B D F 39 3. U
ses a first-class fuel, most published reports of the fuelwood value of melaleucas refer to the larger-growing species in the tropical broad-leaved M. leucadendra group. The wood of M. quinquenervia, for example, is reported to be an excellent fuel and converts into good-quality charcoal. The reported calorific values for the wood and bark of this species are around 18,400 and 25,800 kJ/kg (4,400 and 6,160 kcal/kg), respectively (Wang et al. 1981), but there is great variability in these values between trees (Wang and Littell 1983). The uniquely high heat of combustion of M. quinquenervia bark (equivalent to some coals) is due to the presence of a great amount of fatty substances in the bark (Wang et al. 1982). Keating and Bolza (1982) rated M. cajuputi and M. leucadendra as good fuelwoods, although often difficult to split because of interlocking grain. Gough et al. (1989) reported that the light wood of M. leucadendra was quick to ignite, with sooty acrid smoke initially produced from the burning bark. Posts, poles, stakes and sticks The stems of the larger melaleucas like M. cajuputi, M. leu- cadendra, M. quinquenervia and many other species were regularly used in the round or roughly fashioned for use as posts, poles, piles, mine timbers and general construc- tion materials (e.g. rafters for huts, fencing rails) in the early days of settlement in Australia (Maiden 1889). Posts were said to be durable in contact with fresh or salt water (e.g. M. cajuputi, Blake 1968), although Cherrier (1981) reported that durability of untreated M. quinquenervia posts in the ground was high for 1 year but declined thereafter, and replacement was necessary after about 3 years. In present-day Vietnam, there is widespread use of the roundwood of the indigenous M. cajuputi and the introduced M. leucadendra for piles, poles and general construction materials (Figure 19). A specialised industry exists in Western Australia to supply sticks for use in the lobster-fishing and vegetable- growing industries (Peter White, pers. comm. 2012). Although other myrtaceous species may be used, such as Kunzea sp., sticks derived from natural stands of M. viminea are preferred due to their greater durability. It is believed that lobsters enter pots made from natural materials more readily than they do pots made from synthetic substances. In recent years, about 1.2 million M. viminea sticks/year have been used in making lobster pots. Additionally, large numbers of M. viminea stakes are used each year in the vegetable-grow- ing areas of the Gascoyne region for supporting climbing beans. Presently, these markets are supplied from natural stands but it may be that, in the future, the supply of sticks and stakes could be augmented from plantation sources. Sawn wood The wood of the broad-leaved paperbarks M. cajuputi, M. leucadendra, M. quinquenervia and M. viridiflora has yellowish sapwood, merging gradually into pinkish-brown/ red/grey heartwood. It has a high silica content (0.2–1.0%) which blunts saws and planes. It is hard, heavy and of moderate strength, with wood from native trees giving a green density of c. 1,070 kg/m3 and an air-dry density of c. 750–800 kg/m3 (Keating and Bolza 1982; Bootle 1983). Florida-grown wood of M. quinquenervia has a basic specific gravity of 0.49, a density of 1,070 kg/m3 (green), 640 kg/m3 (air-dry) and 620 kg/m3 (oven-dry) (Huffman 1981). Collapse is slight, with shrinkage about 3.5% radial and 7% tangential (Bootle 1983). Sawn timber tends to check and warp but, if carefully seasoned, it is suitable for general construction and flooring. Boards are difficult to plane and mortice due to interlocking grain but glue well and are good for joinery. Boat knees can be cut from branches using their natural shape.
and loading poles onto a barge for transport to market; and (B) stacks of melaleuca poles at a roadside market A B 40 3. U
ses Woodchips Vietnam is the main producer of Melaleuca woodchips for use in fibreboard production. In 2010, 100,000 t (bone- dry) of Melaleuca woodchips were exported from Vietnam to China, presumably for this purpose. Presently, there are well-advanced plans to establish a medium-density fibre- board (MDF) plant in the Mekong Delta of Vietnam to utilise the Melaleuca resource directly (Stephen Midgley, pers. comm. 2012). The ‘kraft’ pulping potentials of 2-year-old paperbark wood from Vietnamese plantations were reported by Chen and Su (1998, as M. leucadendron). The low pulp yield and high chemical consumption were unfavourable pulping characteristics but the strength index was adequate and bleachability excellent. The authors indicated that older trees might have better pulp qualities. Extractives Organic chemicals produced and stored naturally in plant tissues are numerous and chemically complex. By definition, extractives are the organic chemicals that can be removed from plant tissues by the action of water, including steam, other inert solvents such as alcohol and by mechanically crushing the source materials. The types of extractive from selected Melaleuca species that are of economic importance or have commercial potential fall into two classes: non-volatile (e.g. betaines) extractives and volatile (foliar essential oils). Non-volatile extractives The foliage of a range of Melaleuca species produces com- mercial levels (>2% fresh weight) of betaine (Naidu and Cameron 1999). Betaines are non-volatile, water-soluble compounds and comprise three methylated prolines: N-methylproline, trans-4-hydroxy-N-methylproline and trans-4-hydroxy-N,N-dimethylproline. They are osmo- protectants against stress (e.g. unfavourable temperatures, drought, soil salinity) in tolerant plants and on application (foliar and seed treatment) to stress-susceptible plants can create acquired tolerance. Naidu (2003) believes that the use of betaines to increase stress tolerance in Australian agricultural crops would stabilise and even increase the national income from agriculture. Glycine betaine, a by-product of the sugar-beet indus- try, is currently sourced from Finland and a worldwide shortage is predicted for this solute. Australian melaleucas are a good alternative source of osmoprotectants. Naidu (2003) found that M. bracteata, which accumulates a pro- line analogue, trans-4-hydroxy-N-methyl proline, had the greatest potential of the melaleucas tested for commercial development, because of its adaptability, vigorous growth and high yields. Despite this potential, there have been no recent reports of further development of this opportunity. Research has also shown Melaleuca bark and leaves to be a rich source of phenolic extractives (tannins) (Huffman 1981; Hussein et al. 2007) but no commercial exploitation of phenolics from melaleucas for uses such as wood adhe- sives, leather tanning and as antimicrobial agents has been reported. Novel flavonoids have been identified in the leaf waxes, seeds and honey of several Melaleuca species (e.g. Courtney et al. 1983; Wollenweber et al. 2000; El-Toumy et al. 2001; Yao et al. 2004; Yoshimura et al. 2008). Similarly, various trit- erpenes, some previously undescribed, have been extracted from the leaves, bark, wood and seed of various melaleucas (e.g. Ahmad et al. 1997; Lee and Chang 1999; Vieira et al. 2004; Bar et al. 2008). Habila et al. (2010), for example, have reported the extraction of a triterpene, betulinic acid, from the wood of M. bracteata. They tested this compound, which they state is known for its anti-HIV and cytotoxic activity against malignant versus non-malignant cancer cell lines, and against a number of pathogenic organisms from the genera Trichophyton, Candida and Microsporum. They found that it had ‘great potential’ as an antifungal drug. Foliar essential oils An essential oil is the (usually) hydrophobic liquid contain- ing the volatile compounds that are found in the oil glands or trichomes of a plant. These glands are usually associ- ated with the leaves, although bark, wood or roots of plants may also contain essential oil. The oil is usually obtained by steam distillation, although the expressed oil (as in the case of citrus peel) can also be used. Essential oils are usu- ally associated with species in the families Myrtaceae and Rutaceae, although they do occur in some other families. Commercially important oils Relatively few Melaleuca species have essential oils of com- mercial interest. One of the first species to be exploited commercially for its foliar oil was M. cajuputi subsp. caju- puti in the Maluku archipelago of Indonesia, probably in the first part of the eighteenth century. It was one of the first products imported to Europe from South-East Asia by the Dutch (Gildemeister and Hoffman 1961, cited in Lowry 1973), because of its reputation as a panacea in the treatment of all kinds of diseases. Cajuput oil is produced currently in South-East Asian countries including Indo- nesia, Cambodia and Vietnam and annual production potentially exceeds 600 t (Doran 1999a, b). This oil is rich in 1,8-cineole (typically 40–60% of total oil) (Doran 1999a, b; Pujiarti et al. 2011), as is medicinal Eucalyptus oil but at slightly higher proportions (70% or more). Cajuput oil acts as a mild antiseptic and is especially useful for treat- ing respiratory ailments, but also finds use in a wide range of personal-care (e.g. ointments and liniments) and 3. U ses
41 household products (Doran 1999a, b; Lassak and McCa- rthy 2011). Niaouli oil from the 1,8-cineole-rich form of M. quinquenervia (40–80% 1,8-cineole) was, until recently, produced in Madagascar from plantations yielding 1.5–2.0 t of oil/year. This oil was used for similar purposes to cajuput oil (Ramanoelina et al. 2008; Lassak and McCarthy 2011). Production of niaouli oil in New Caledonia from natural stands of M. quinquenervia (Trilles et al. 1999, 2006) has now also ceased after many years of exploitation, although there is new interest in producing this oil type in Vietnam (Le Dinh Kha, pers. comm. 2012). The basis for the commercial interest in, and develop- ment of, the Australian tea tree oil industry—utilising mainly plantations of M. alternifolia established in north- ern New South Wales and northern Queensland and plantings made outside Australia—can be traced back to the 1920s. It was then that the medicinal properties of the oil were first studied and reported (Penfold and Grant 1925). The terpinen-4-ol-rich oil produced from M. alternifolia was found to be a powerful antimicro- bial agent. It has demonstrated its ability to serve as an antiseptic, antifungal, antiviral, antibacterial and anti- inflammatory agent in multiple studies and is relatively safe for topical applications (Southwell and Lowe 1999; RIRDC 2007; Lassak and McCarthy 2011). It is incorporated into many personal-care and household products and is seeing increasing use in products designed for agricultural and animal-husbandry purposes (Figure 20). Annual produc- tion in Australia of Australian tea tree oil is estimated to be in the order of 400–500 t, worth approximately A$15–20 million at the farm gate. The three abovementioned species/chemotypes provide the bulk of the commercial production of essential oils from the genus at present. In addition, there is sporadic interest in the following oils. Linalool-rich oil is sourced from specific provenances of M. ericifolia. Linalool, with its fruity notes, is of value to the flavour and fragrance industries and, although it can be produced synthetically, there remains a market in aroma- therapy where natural linalool is preferred (Coppen 1995).
priate chemotype of M. quinquenervia. This compound, presently sourced from a diminishing world supply of cabreuva oil (Erich Lassak, pers. comm. 2007), has an established market in perfumery where it is used as a base note in many delicate, flowery odour complexes (Bauer et al. 1997). Melaleuca quinquenervia was shown to yield and coppice well in plantations in northern Queensland (Doran et al. 2007) before the recent arrival of myrtle rust to Australia (see Chapter 5). E-methyl cinnamate has been derived from a northern Queensland form of M. viridiflora (Hellyer and Lassak 1968; Brophy and Doran 1996). Methyl cinnamate is a colourless, crystalline solid with a fruity, sweet-balsamic Figure 20. A sample of the many products that utilise Australian tea tree oil 3. U ses
42 odour and its uses include as a flavour enhancer and in perfumery (Bauer et al. 1997). A small market exists for the natural product, but it can be produced artificially at relatively little cost and there is strong competition from other natural sources. Platyphyllol, a b-triketone, is found in M. cajuputi. It has been identified as having ultraviolet-blocking attributes and insecticidal properties but it is not being produced commercially at this time (Yaacob et al. 1989; Brophy and Doran 1996; Doran 1999a, b).
et al. 2003, 2005). A small production of this oil has com- menced from natural stands and plantations in Western Australia. The producer claims the oil has perfumery and therapeutic properties. An objective of work undertaken for this book was, if possible, to identify other species/chemotypes of melaleuca with commercial potential. The results of this work are summarised in the ‘Species accounts’ (Chapter 7) and in Appendix 1, which provides a quick reference to the oil type(s) present in individual species. Inter- and intra-specific variation Essential oils from a plant species are not necessarily chemically uniform. There can be, and usually is, variation in the compounds contained in the oil and their relative percentages. For this reason, chemists studying the essen- tial oils of plants try to examine samples of the oils from a number of plants, preferably from many different sites. Variation in the essential oils may be continuous over a geographical region, or it can be quite discrete. This latter occurrence leads to the finding of different chemotypes of the plant, i.e. plants which, though morphologically the same, produce different essential oils. It is possible, because of inadequate sampling, to find two different oil composi- tions within a species (i.e. two chemotypes) when, in fact, they just represent the extremes of a continuous variation. Examples of both types of variation as they apply to the main (M. quinquenervia, M. alternifolia and M. cajuputi) and one minor (M. ericifolia) commercial oil-producing species are discussed below. The possible presence within a species of these types of variation should be borne in mind when interpreting the results given in the fol- lowing sections. The essential oil of M. ericifolia has been studied for over 50 years. A 2004 study examined its essential oil content over its natural geographical range, which extends from coastal regions near Newcastle, New South Wales, in the north to Tasmania in the south (Brophy and Doran 2004). The study looked particularly at the amount of 1,8-cin- eole and linalool in the oils and the results are shown in Figure 21. Generally, the amount of 1,8-cineole increases from Newcastle southwards to Tasmania, and the amount of linalool decreases concomitantly. As the essential oil of M. ericifolia is important because of its linalool content, it is important to source the oil from plants in the north of its range. But there is a continuous variation in oil contents so, in this case, it is not correct to refer to a cineole chemotype or a linalool chemotype. Melaleuca quinquenervia, in contrast, is a species known to contain chemotypes. There are two distinct chemotypes of this species; chemotype I contains E-nerolidol as the major component (in amounts of up to 95%) of the oil, while chemotype II contains major amounts of either 1,8-cineole or viridiflorol (or both), as well as lesser amounts of other terpenes. There is no plant producing an oil containing significant amounts of all three oils (E-nerolidol, 1,8-cineole and viridiflorol). Viridiflorol production is catalysed by terpene synthase enzymes. The genes coding for these enzymes are present in the genome of all plants of the species, but are expressed only in the vir- idiflorol chemotype (Padovan et al. 2010). The Australian distribution of the two chemotypes has been mapped and is shown in Figure 22 (Ireland et al. 2002). The chemotype containing major amounts of 1,8-cineole is the basis of the niaouli oil industry. Melaleuca alternifolia exists in several chemical forms (chemotypes), although among them there are only three principal forms (Butcher et al. 1994; Homer et al. 2000). These three chemotypes contain terpinen-4-ol (up to 50%), the chemotype on which the tea tree oil industry is based, 1,8-cineole (up to 60%) and terpinolene (up to 50%). Pro- duction of the oils of these three chemotypes is controlled by three different enzymes (Keszei et al. 2010a, b). The 1,8-cineole chemotype is not used commercially, and the oil presents a similar oil profile to a eucalyptus or niaouli oil. This particular type of oil is very common in species of Melaleuca (see Appendix 1). The terpinolene chemotype found in M. alternifolia (Southwell et al. 1992) also occurs in M. trichostachya (Brophy 1999). Melaleuca cajuputi subsp. cajuputi, the basis of the cajuput oil industry in South-East Asia, contains up to approximately 60% of 1,8-cineole, together with lesser amounts (approximately 10%) of limonene, a-terpineol and viridiflorene, and spathulenol (up to 30% in some cases). There are, however, a few isolated cases of this spe- cies, from northern Western Australia, producing an oil containing large amounts of E-nerolidol and virtually no 1,8-cineole (J.J. Brophy et al., unpublished data). Species by oil type With 290 species in the genus Melaleuca, it is not sur- prising that their leaf oils have much variation, resulting in many different types of oils. In this short section, we will review this variation and show what a wide range of chemicals is contained in Melaleuca leaf oils. The full data from the analyses are provided on the internet, accessible at Kataloq: files files -> Информация по результатам плановой проверки, проведенной комитетом здравоохранения Курской области files -> Penitensiar sistemdə Vərəmə nəzarət üzrə TƏLİmat Yüklə 6,86 Mb. Dostları ilə paylaş:
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