Changes

*''Eucalyptus citriodora'' Hook. (1848), *''E. Eucalyptus melissiodora'' Lindley (1848), *''EEucalyptus variegata'' F. v. Mueller (1859),*''Eucalyptus maculata'' Hook. var. ''citriodora'' (Hook.) Bailey (1900).

''C. citriodora'' has been extensively planted as an ornamental tree in many regions of the world, including the Mediterranean area, and has been planted for commercial purposes in South America, especially Brazil (6 million trees), southern China, India, Sri Lanka, Congo (Zaire), Kenya and most countries in southern Africa and in Fiji. In South-East Asia it is mainly planted in Peninsular Malaysia. In Thailand it was introduced in 1949, but commercial plantations no longer exist.

The timber of ''C. citriodora'' is used for general and heavy construction such as frame and bridge construction, flooring, cladding, tool handles and case manufacturing. The wood of young trees has been successfully used for certain grades of pulp and paper, but wood from old trees is generally not suitable because of its high extractive content and high density. However, the tree is planted as one of the better eucalypts for low regions in tropical and subtropical regions for pulp production. Young trees or coppice stems produce straight poles or posts which can be pressure impregnated with preservatives for many industrial purposes. In Brazil large plantations have been established for charcoal production. It is also used for reforestation.

Commercial essential oils of ''C. citriodora'' are colourless to pale yellow with a strong, very fresh rosy-citronella scent and a sweet balsamic-floral dry-out. They consist principally of citronellal and other monoterpenes including citronellol, neral, isopulegols and smaller amounts of 1,8-cineole, linalool, geraniol,α-terpineol, @c-cadinene andβand β-caryophyllene. Oils are assessed on their odour characteristics and the portion of citronellal in the total aldehyde content. Producers of hydroxycitronellal prefer the higher citronellal levels.

The wood of ''C. citriodora'' has a white or cream sapwood up to 60 mm wide and is very susceptible to ''Lyctus'' borer attack; the heartwood is pale grey-brown to dark brown. The sapwood is permeable but the heartwood extremely resistant to preservative treatment. The grain is straight or interlocked and occasionally wavy, the texture open and coarse. The timber is hard, strong and tough. Air-dry density of wood from natural stands is about 1000 kg/m³(12% moisture) with basic density of 800 kg/m³. It saws easily, planes well, but is rather difficult to nail and prone to checking and collapsing during drying. The timber is susceptible to marine borer and termite attack. Chemical pulp of reasonable quality can be obtained from wood of young (9-years-old) trees. See also the table on wood properties.

Both citronellal and the derived hydroxycitronellal are produced from two other sources, citronella oil from the citronella grasses ( ''Cymbopogon nardus'' (L.) Rendle and ''C. winterianus'' Jowitt) of Sri Lanka and Indonesia, and turpentine. Price and the slight odour differences caused by accompanying minor constituents determine customer preference. Natural citronellal has a marketing advantage over synthetic, turpentine-derived citronellal, especially in flavour applications.

*Medium to large, often straight stemmed tree, 25-40(-50) m tall, of handsome appearance, with pale grey, cream or pink powdery bark, smooth throughout, decorticating in flakes, and somewhat sparse foliage. Twigs slender, slightly flattened, light green, tinged with brown. *Leaves petiolate, strongly lemon-scented when crushed; seedling leaves opposite for a few pairs then alternate, peltate, ovate, 6.5-17 cm × 2.3-7.5 cm, pale green, slightly discolorous, setose; juvenile leaves alternate, ovate to broad-lanceolate, up to 14-21 cm × 4.5-8 cm, in some plants setose, pale green and peltate for many pairs, in others becoming glabrous and glossy green soon after the seedling stage; stems, petioles and leaves setose with bristle glands up to 0.5 cm long in both the seedling and juvenile stages; intermediate leaves petiolate (up to 2.2 cm), disjunct, broad-lanceolate, 13-30 cm × 2-5 cm, apex acute to obtuse; adult leaves on flattened petioles 13-22 mm long, disjunct, lanceolate to narrow-lanceolate, 7-22 cm × 0.5-2.2 cm, concolorous, very glossy, green, venation very densely reticulate with numerous large island oil glands, lateral veins just visible, at 3535°-5050°, intramarginal vein distinct, up to 1 mm from margin, stomata on both surfaces. *Inflorescence an umbelliform condensed and reduced dichasium (usually called a conflorescence), combined into clustered terminal or sometimes axillary, corymbose panicles; peduncle terete, 3-8 mm long; umbels 3-flowered; pedicel 1-6 mm long; buds pedicellate, clavate, up to 10 mm × 6 mm, scar absent; operculum hemispherical, 3-4 mm long, 4-5 mm wide, apiculate; flowers creamy-white; hypanthium hemispherical, 5-6 mm × 4-5 mm; stamens numerous, prominent, 6 mm long, spreading 12 mm across, all fertile with subulate filaments and oblong, dorsifixed anthers dehiscing by parallel slits; pistil inferior with 3-celled ovary. *Fruit a capsule, truncate-ovoid to urceolate, 8-15 mm × 7-11 mm, brown, often warty, 3-locular; disk about 2 mm wide. *Seed dorsiventrally compressed, 2-3 mm × 1.5-2.5 mm, glossy red-brown, with a median dorsal keel. *Seedling with epigeal germination.

''C. citriodora'' belongs to the spotted gums, part of the bloodwood group of eucalypts. Under the informal classification of Pryor and Johnson (1971), ''C. citriodora'' (as ''Eucalyptus'' ) was placed in the series ''Maculatae'' of the subgenus ''Corymbia'' of ''Eucalyptus'' , along with its close relatives ''E. maculata'' Hook. and ''E. henryi'' S.T. Blake. Hill and Johnson (1995) have placed the bloodwoods in a new genus ''Corymbia'' K.D. Hill & L.A.S. Johnson. Under this classification, which is adopted here, ''Eucalyptus citriodora'' becomes ''Corymbia citriodora'' of the series ''Maculatae'' and section ''Politaria'' . Four closely related species are recognized in this section: ''C. citriodora'' , ''C. maculata'' (Hook.) K.D. Hill & L.A.S. Johnson, ''C. henryi'' (S.T. Blake) K.D. Hill & L.A.S. Johnson and a new species ''C. variegata'' (F. v. Mueller) K.D. Hill & L.A.S. Johnson. The latter one was reinstated from synonymy, to cater for the populations in northern New South Wales and south-eastern Queensland that are morphologically intermediate between ''C. citriodora'' and ''C. maculata'' and whose leaves are not lemon-scented. In regions where the distributions of ''C. citriodora'' and ''C. variegata'' overlap intergrading populations occur with a gradient in the amount of citronellal in the leaves.

Seedlots of ''C. citriodora'' vary in germination rate but usually average 30-50%. Rapid and complete germination is achieved under moist, warm conditions (25-30°C is optimal in the laboratory) in the presence of light. In seed tests a leachate from the seed has been found to inhibit germination on filter paper. Direct seeding into carefully prepared ground has been successful in southern Africa, but is unreliable and not generally recommended, as favourable weather and freedom from weeds are critical to success. Containerized planting stock is preferred, because bare-rooted seedlings tend to show poor lateral root development and losses due to transplanting shock. The seeds are relatively large for a eucalypt and can be sown directly without pretreatment into containers filled with a sterilized freely draining mixture of loam and sand and covered with a light sprinkling of fine sand. ''C. citriodora'' , like other eucalypts, is highly susceptible to damping-off and other fungal pathogens in the nursery. Disease problems can be limited by good hygiene, reducing watering and shade, and allowing good ventilation. Seedlings are planted out in the field when they reach a height of about 25 cm, 10-12 weeks after sowing. This should coincide with the onset of the rainy season in tropical countries. ''C. citriodora'' can be multiplied vegetatively by micropropagation, but so far this technique has only been applied experimentally. Propagation by cuttings is very difficult.

Intensive site preparation by ploughing is beneficial; on compacted soils deep ripping may also be used. Spacing varies, depending on the purpose of the plantation. When grown solely for oil production with frequent coppicing, 3 m × 1.5 m (2222 plants/ha) is appropriate. For fuelwood, poles or charcoal production with harvesting cycles of 7 years, a spacing of 3 m × 2 m (1667 plants/ha) is common. Several planting arrangements have shown favourable economic returns in India: block plantings at 1 m × 1 m spacing in a farm forestry programme; planting along bunds at 1-2 m spacing in an agroforestry programme; and interplanting essential oil-yielding grasses ( ''Cymbopogon'' spp.) with ''C. citriodora'' at 2-3 m × 2 m spacing in a social forestry programme, to obtain essential oil as well as fuelwood and pole wood.

Plantations are not normally irrigated but good results have been achieved in trials in Pakistan, where irrigated ''C. citriodora'' intercropped with such crops as wheat, maize, berseem ( ''Trifolium alexandrinum'' L.) and sesame ( ''Sesamum orientale'' L.) grew to 16.4 m in height with a diameter at breast height of 17.7 cm at 7 years.

Within Australia ''C. citriodora'' has remained relatively free of diseases and pests. In Brazil, it has been damaged sometimes by a range of diseases including: damping-off and leaf spot caused by ''Cylindrocladium'' spp., a rust ( ''Puccinia psidii'' ), and a stem canker ( ''Cryphonectria cubensis'' ). Gummosis and cankers from infection by ''Endothia havanensis'' have also been noted. In China, gummosis induced by ''Cytospora'' sp. and ''Macrophoma'' sp. has caused severe damage. In India, it is susceptible to a range of diseases including: ''Cylindrocladium'' seedling blight, a rust ( ''Melampsora'' sp.), pink disease ( ''Corticium salmonicolor)'' , and ''Ganoderma'' root rot. The root rot fungus ''Pseudophaeolus baudonii'' attacked plantings of ''C. citriodora'' in Sege (Ghana), causing 50% mortality over 3 years. Most problems arise on sites with high rainfall and humidity. Prevention is the best cure, so appropriate nursery techniques should be applied and planting sites should be selected carefully.

''C. citriodora'' is very susceptible to termites. In India, ''Microcerotermes minor'' can cause 20-30% mortality and ''Odontotermes horni'' over 10%. Use of dangerous pesticides such as dieldrin, aldrin and chlordane for the protection of seedlings against termites has been phased out in most countries. Carbosulfan, a non-persistent carbamate insecticide, is being used as an effective replacement in several African countries. A range of defoliating insects and a stem borer ( ''Apate indistincta'' ) have been noted as causing occasional damage to plantations.

In the wild ''C. citriodora'' is locally abundant over a wide area and is not considered to be at risk. In addition, it is very widely planted and local landraces in many countries are another reserve of genetic material. Seed trees have seldom been tested for their oil characteristics in Australia, and seed exported from Australia for plantation establishment could be representative of one or more of the four chemical forms of ''C. citriodora'' . When propagating ''C. citriodora'' for oil production, care should be taken that the seed has been selected from provenances with oil characteristics that meet the requirements of the intended market. The Australian Tree Seed Centre of CSIRO Forestry and Forest Products in Canberra maintains a collection of seed of provenances of ''C. citriodora'' including some individual tree collections that have been tested for oil characteristics.