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Eucalyptus citriodora Hook.

Myrtaceae
Lemon-scented gum

Source: James A. Duke. 1983. Handbook of Energy Crops. unpublished.

  1. Uses
  2. Folk Medicine
  3. Chemistry
  4. Toxicity
  5. Description
  6. Germplasm
  7. Distribution
  8. Ecology
  9. Cultivation
  10. Harvesting
  11. Yields and Economics
  12. Energy
  13. Biotic Factors
  14. References

Uses

Leaves yield a lemon-scented oil rich in citronellal, and favored in perfumery. The wood is good for saw-timber, used for general construction, poles, railroad ties, and tool handles. Bark may contain up to 12% tannin. Kenyans favor the honey produced by this species.

Folk Medicine

Reported to be antiseptic and fumigant. Cubans place the leaves under the sheets of fever patients, and inhale the steam from boiled leaves for cold and various pulmonary problems. Cubans also poultice the leaves onto ulcers, wounds, and other skin ailments. Guatemalans decoct the leafy shoots for coughs (Morton, 1981). Orally administered leaf extracts in rabbits artifically diabetic, produced temporary hypoglycemia and reduced the blood sugar levels (Watt and Breyer-Brandwijk, 1962). Myrtillin, in the leaf extract, is said to induce a temporary hypoglycemia (Atal and Kapur, 1981).

Chemistry

Dayal reported betulinic and ursolic acids, eucalyptin and b-sitosterol in the leaves. Glabrous leaves may contain oil with 65.5% citronellal, 12.2% citronellol, and 3.6% isopulegol; hairy leaves contain more oil with 86.6–90.1% citronellal, 4.6–6.0% citronellol, and 0.7–0.8% isopulegol, 1-pinene, b-pinene, and isovaleric aldehyde are also recovered (Morton, 1981). Bark contains ca 9% tannin (Watt and Breyer-Brandwijk, 1962). The young leaf is reported to contain citric-, glutaric-, malic-, quinic-, shikimic- (carcinogenic), and succinic-acids (Watt and Breyer Brandwijk, 1962). Leaves and fruits test positive for flavonoids and sterols.

Toxicity

Citronellal found in Eucalyptus and Melissa is reported to be mutagenic (Lewis and Elvin-Lewis, 1977).

Description

Evergreen tree 24–40 m high with tall straight trunk 0.6–1.3 m in diameter, and thin, graceful crown of drooping foliage. Bark smooth, gray, peeling off in thin irregular scales or patches and becoming mottled, exposing whitish or faintly bluish inner layer with powdery surfaces appearing dimpled. Twigs slender, slightly flattened, light green, tinged with brown. Leaves alternate, narrowly lance-shaped, 10–20 cm long, 1–2.5 cm wide, apically acuminate, basally acute, entire, glabrous, thin, light green on both surfaces, with many fine parallel straight veins and with vein inside edge. Corymbs terminal and at leaf ba"s, to 6 cm long, branched. Flowers many, 3–5 on equal short stalks (umbels) from ovoid buds 8–12 mm long, 5–8 mm wide. Stamens many, threadlikes, white, 6 mm long, spreading ca 12 mm across, anthers with long gland. Pistil inferior 3-celled ovary and long, stout style. Capsules few, urn-shaped or ovoid, narrowed into short neck, 10–12 mm long, 8–10 mm wide, brown with scattered raised dots. Seeds few, irregularly ellipsoid, 4–5 mm long, shiny black (Little, 1983).

Germplasm

Reported from the Australian Center of Diversity, lemon-scented gum, or cvs thereof, is reported to tolerate clay, drought, gravel, laterites, light frosts, podzols, poor soil, and slopes, but is not very tolerant of waterlogging. The hybrid with E. torelliana is showing promise in Nigeria (NAS, 1980a). Gupta et al. (1981) obtained multiple shoots from 20-year old terminal bulbs in culture. Shoots were also obtained from seedling explants. They estimate they can produce 100,000 plants from one mature tree bud in one year.(2n = 20, 22, 28)

Distribution

Said to occur naturally only on the central and northern coasts of Queensland, Australia, but to fare well in much of Africa, Brazil, California, Hawaii, India, even Portugal.

Ecology

Said to grow where the rainfall, mostly summer, is 6 to 13 dm, with 5–7 month dry season, withstanding high temperatures (29–35°C mean monthly maximum) and light frosts. In tropical and subtropical arid to semiarid zones, in infertile clays, laterites, poor and gravelly soils and podzols, preferrably well drained.

Cultivation

In Zimbabwe, seeds are broadcast successfully on the ashes of recently burned tracts. More usually seedlings are transplanted from the nursery. Seed require no special treatment.. Though needing protection from frost and weeds when young, older saplings show more tolerance to both. According to Irvine (1961), seedlings transplant badly.

Harvesting

For oil extraction, trees are not allowed to mature to the timber stage. Instead, they are lopped for the foliage; sucker shoots produce copious foliage.

Yields and Economics

Tanzania plantations, harvested on an 8-year coppice, produced an annual 15 m3/ha. Back in 1925, the essential oil from this species commanded twice the price of that of E. globulus (MacMillan, 1946).

Energy

Firewood yields run 10–21 m3/ha/yr (Fenton et al., 1977). The hard heavy wood (sp. grav. 0.75–1.1) burns steadily and makes a good charcoal with an ash content of 1–2%. This is the chief charcoal species of the Brazililan steel industry.

Biotic Factors

Browne (1968) lists the following as affecting this species: (Bacteria) Agrobacterium tumefaciens. (Fungi) Armillaria mellea, Fusarium spp., Ganoderma colossum, G. lucidum, Phytophthora parasitica, Polyporus rubidus, Puccinia psidii, Sclerotinia fuckeliana, Trametes cubensis, Verticillium albo-atrum. (Coleoptera) Anomala cupripes, Dicasticus affinis, Elytrurus griseus, Entypotrachelus meyeri, Systates surdus, Xyleborus truncatus. (Hemiptera) Atelocera stictica, Eucalyptolyma maideni. (Isoptera) Ancistrotermes amphidon, Coptotermes truncatus, Microtermes spp., Pseudacanthotermes militaris. (Lepidoptera) Carea angulata, Colocleora divisaria, Neocleora nigrisparsalis, Nudaurelia krucki, Strepsicrates holotephras, Sylepta balteata, Thalassodes sp., Uzucha borealis. (Orthoptera) Schistocerca gregaria.

References

Complete list of references for Duke, Handbook of Energy Crops
Last update Tuesday, January 6, 1998 by aw