Eucalyptus

Read about Eucalyptus in the Standard Cyclopedia of Horticulture

Eucalyptus (Greek, eu, well; kalypto, to cover as with a lid: the petals and usually also the calyx-limb fused and covering the flower before anthesis, then falling off in the form of a lid, or cover). Myrtaceae. Gum-tree. Plate XXXIX. Mostly trees, frequently of immense size, a few of the alpine and sub-alpine species shrubby, much grown in California and the Southwest for their ornamental value, as windbreaks and avenue trees, for fuel, and especially for their timber. Leaves simple, entire; in the seedlings and on young shoots of many species horizontal, opposite, sessile, and cordate; in the adult mostly vertical, alternate, petiolate (rarely opposite and sessile), and varying from roundish to lanceolate-acuminate and falcate; always rigid, penniveined, glabrous except rarely on the young shoots, sometimes covered with a glaucous wax: fls. white, rarely yellowish or some shade of red, in umbels of 3 to many, rarely solitary, the umbels solitary and axillary for paniculate or corymbose; calyx-tube obconical, campanulate, ovoid. or oblong, adnate to the ovary at the base; petals and calyx-lobes connate, forming a lid, or cap, which separates from the calyx-tube by a circumscissle dehiscence; lid sometimes plainly double, the outer cap then derived from the calyx-limb, the inner cap from the petals; stamens numerous; anthers small; style undivided: fr. a caps, partially or wholly inclosed in the adherent calyx-tube, opening at the top by 3-6 valves; seeds numerous, small, mostly angular.—About 300 species, all native of Austral, and the Malayan region. Related to Angophora and to Syncarpia, but distinguished by the absence of distinct petals. The genus Eucalyptus was monographed in part by Baron von Mueller in his Eucalyptographia (cited here as F. v. M. Eucal.), in which 100 species are illustrated (1879-84). The genus is now receiving exhaustive treatment by J. H. Maiden in his "Critical Revision of the Genus Eucalyptus," appearing in parts, with numerous plates. This author also furnishes the best information regarding the uses and timber of the various species, in his "Native Useful Plants of Australia." Bentham described 135 species in his "Flora Australiensis," vol. 3 (1866). The Australasian Association for the Advancement of Science published a very useful key by J. G. Luehmann in 1898. The most exhaustive American work on the genus is United States Forestry Bulletin No. 35, "Eucalypts Cultivated in the United States," by A. J. McClatchie. University of California Agricultural Experiment Station Bulletin No. 196, by Norman D. Ingham, is a practical guide for planters, with descriptions of the more important species. The United States Forest Service, the California Station, and the California State Board of Forestry have all issued smaller bulletins on this subject. Inflated claims have been made for eucalyptus culture, and authentic publications should be secured if one contemplates planting them extensively. Eucalyptus is a group adapted to semi-tropical and warm temperate regions. But few species are really hardy. E. globulus has been very widely distributed over the globe through the persevering efforts of the late Baron von Mueller; it is frequently planted in the malarial regions of warm climates, as at the Campagna at Rome, with very beneficial effect. (Sanitarians will be interested in "Eucalyptus in Algeria and Tunisia, from an Hygienic and Climatological Point of View, by Edward Pepper, Proc. Amer. Phil. Soc. 35:39-56.) In England, the same species is grown extensively for subtropical gardening, on account of its distinctive glaucous hue and symmetrical growth, but in that climate it needs the protection of glass in winter. This is by far the most important genus of timber trees introduced into California. The ordinary blue- gum, E. globulus, has been grown in large numbers and is still the favorite for general planting. Its hard and durable wood is replacing oak and hickory to some extent for insulator pins, wheel-wrights' work, flooring, tool-handles, and furniture. Although pale in color, it takes a good polish, possesses a beautiful grain, and is readily stained. Furniture made from blue-gum wood and properly stained has every appearance of mahogany. The chief drawback to the use of eucalyptus for lumber is the tendency of its logs to end-check while curing, thus involving considerable waste. As a windbreak and fuel tree it is unsurpassed, since it is of rapid, erect growth and the timber is easily split. Its foliage has been distilled in large quantities for the oil it contains, practically all of the eucalyptus oil now sold in the United States coining from home-grown trees. In addition to the blue-gum, E. rostrata and especially E. tereticornis are grown for railroad ties, piling, interior finish and furniture. E. resinifera is a hardy eucalypt yielding a good timber not so liable to check as that of some others; it has been but little grown in America thus far. E. corynocalyx is a good drought- resistant species for districts with mild winters, and its wood is of the best. E. crebra will grow under a greater range of conditions than perhaps any other and is especially suited to the hot and dry interior valleys. Other drought-resistant eucalypts are E. microtheca and E. polyanthemos, while the most resistant to frost are E. crebra, E. rostrata, E.tereticornis, E. globulus, E. viminalis, E. rudis, E. robusta, and E. resinifera. The species most cultivated as ornamentals are E. ficifolia, E. leucoxylon., E. sideroxylon var. rosea, E. Risdonii, E. erythronema and E. polyanthemos. Persistently repeated accounts of heights ranging from 325 to 500 feet for certain eucalypts are erroneous, as indicated under E. amygdalina var. regnans. Although the eucalypti are not exclusively, and some species not even prominently horticultural, yet because of the great general interest attached to them and because of their varied uses, it is thought best to discuss them rather fully in this Cyclopedia. Culture of eucalyptus in California. The following directions for the propagation of Eucalyptus are adapted very largely from Bulletin No. 196 of the California Experiment Station, entitled "Eucalyptus in California, by Norman D. Ingham (1908). The necessary conveniences for the propagation of XXXIX. the seedlings are: seed-boxes or flats, a good soil, seed true to name, plenty of convenient water, and in most localities shade for the young plants. The seeds of most species may be gathered at all times of the year, although the greater amount mature during the summer and fall. The seed-cases should be gathered from the trees when the valves begin to open and placed on sheets of canvas in the direct rays of the sun, which will open the valves, allowing the seed and chaff to fall out. The number of fertile seed to the pound is very high; the average number of transplanted plants raised to the pound is 12,000. Eucalyptus seed will germinate and grow in nearly any soil but the best results are secured when the seeds are sown in a light loam, while a medium loam mixed with about one-quarter well-rotted horse- manure should be used in the transplanting flats. The time to sow the seed varies somewhat with the locality, but as a general rule the seed should be sown in May or June and the seedlings from these sowings will be large enough to be set out in the field the following spring, if they receive proper care while young. The seed is usually sown broadcast in the seed-flats and the young plants transplanted once before being set in the field. Some persons take the trouble to sow one seed in a place and space them in the flats; by this method transplanting is unnecessary. Others sow the seeds in hills and practise thinning, instead of transplanting before setting out in the field. This last method is used in the warmer districts with good success, because of the great trouble experienced in transplanting during the hot summer months. Whichever method is used, fill the flats to a depth of 3 or 4 inches with the prepared soil, pressing it down firmly in the boxes, then sow the seeds and cover them to a depth of about ⅛ inch with the same soil, sand, or sawdust, pressing this covering firmly over them. The seed- flats should be kept damp through the heat of the day, until the young plants break the ground, then care must be taken not to use too much water and that there is a good circulation of air over the flats, or damping- off is liable to occur. This disease can be prevented by using practically no water on cloudy days and only in the mornings on clear days. If the seeds are sown broadcast in the flats, when the young plants have reached a height of 2 to 3 inches, they can be transplanted to other flats of prepared soil and spaced from 1¼ to 2 inches apart. The beet results in transplanting are secured if the plants are hardened-off for a few days beforehand by checking the water supply, allowing them to become quite dry. The soil into which the young plants arc tranplanted should be kept damp, and the plants should be protected from the direct rays of the sun for a few days. The lath-house or the screens are necessary to supply shade for the young plants and will also protect the seeds in flats from the ravages of birds and the young plants from the frosts during winter months, before the time for setting in the field. The time to set the plants in the field varies with the climatic conditions or localities and whether the plants are to receive irrigation or not. In localities in which frosts are common through the winter months, it is advisable to set the trees put as early in the spring as possible without endangering them to a late frost and still have them receive the benefit of the late rains, so that they will have a full season's growth to withstand the frosts of the following winter. If the trees are to be irrigated, they may be set out later in the season without danger of loss from want of moisture. To insure a good stand, the plants should not be under 6 or over 20 inches in height when set in the field; to a certain extent, the smaller the plants when set out, the better the results afterward, although the size varies somewhat with the species and the locality. In many species the roots are as long if not longer than the plant's own height above ground. This is a family of plants that will not stand a large amount of mutilation to the root-system; consequently better results are secured from setting out small plants. If the soil is heavy rich loam, the trees may be planted as close as 6 by 6 feet apart unless irrigation is to be practised. In the latter case, 4 by 8 feet would be the right distance, thus leaving an 8-foot space for plowing out the irrigating-ditches each year. If it is a lighter soil on which the planting is to be made, 8 by 8 feet is the proper distance, or 6 by 10 feet, if irrigation is to be practised. The close planting has a tendency to sacrifice the diameter growth in favor of the height, also making more erect trees and forming a perfect canopy with their crowns that will shade the soil, nearly preventing evaporation, as well as any vegetable growth on the forest floor. Close planting matures a greater number of perfect trees, and is especially recommended when straight poles are desired. The plants should be blocked out in the flats before being brought into the field, by drawing a sharp knife between the rows. If care is taken to set out the young plants with this small amount of soil around the rootlets, the shock caused in transplanting is reduced to a minimum. Each planter should carry a trowel, to make the holes that are to receive the young plants at the intersection of the marked -lines. These holes should be of such a depth that the plants can be set from ½ to 1 inch lower in the soil than they originally were in the flats. Each plant should have the soil pressed firmly about it and receive a small amount of water, unless the soil is moist from recent rains. In order to provide a mulch, thus checking evaporation and also to kill the weeds, cultivation should be conducted in the new plantation as long as possible without danger of injuring the young trees by driving a horse between them. The plantings generally may be cultivated for the first season and part of the second before the limbs of the trees spread out and interlap so that it is impossible to drive between the rows. It is an acknowledged fact that the only way to secure a good stand, and give the trees a start, is to cultivate and take care of the plantings from the time of setting out. However, a number of groves have been set out on land that is too hilly or rocky to cultivate and the trees have made fair growths. Thinning of the young trees is an important practice, as it is not good management to set out just the number of trees that one expects to mature. A planting upon any good soil may with advantage be set out 6 by 6 feet apart (1,210 trees to the acre), and at the end of the first year a rigid thinning should be started, removing with a grub-hoe all weak, inferior, or injured trees. This thinning should be conducted until only the strong and healthy trees, or a certain number, remain to the acre. By this method some trees will stand at the original distance that they were planted, while others will stand at multiples of that distance. The extra cost of close planting will never be noticed when the largest possible stand of healthy trees is guaranteed, which is practically the case under this method. If thinning is carried out by a set plan, removing every other one or two trees, many strong and healthy trees will be sacrificed. All limbs that have a tendency to deform the trees should be removed each year. After the third or fourth year, the trees will have grown to such a height that to remove the limbs may prove impractical in most cases. At this period (the fourth or fifth year) there enters a new problem: the removal of the poorer trees for wood and stakes to allow the remainder a larger area of soil to draw upon and a greater space above ground to extend their branches. At this time the trees on an acre can be reduced to a certain number, leaving these to grow for telephone poles, ties, and lumber, or the entire grove may be cut for stakes and wood. Second-growth eucalyptus.—In three to six weeks after the trees have been felled, the sprouts will start out from the stumps. These sprouts are produced in abundance and if properly thinned will soon replace the cut forest, thus providing a second growth of fuel or timber in much less time than was required with the original grove. These remarks apply probably to all species of eucalyptus, certainly to all sorts experimented with in California up to the present time. Taxonomy of the cultivated eucalypti. All of the keys used for the identification of species are more or less artificial. No satisfactory natural classification has yet been devised. While the following key is designed to aid in the making of determinations rather than to express relationships, species known to be closely related are placed near each other in the text so far as this can be conveniently done. For the ready determination of species in this critical genus, it is necessary to have adult leaves, buds, flowers, and mature fruit; immature fruits are often very misleading. Allowance should always be made for extreme forms, since only normal specimens are here described. This applies particularly to size of leaves. Unless otherwise stated, the leaf description is drawn from foliage on mature stems. The juvenile foliage, i.e., on young seedlings and on suckers, is usually very different, the leaves often broader, blunt, sessile, and of a different color. E. annulata, Benth. Shrub or small tree with characters of E. cornuta, except as follows: Lvs. narrow-lanceolate, acuminate: lid 6-8 lines long, usually incurved: fr. depressed-globose, 4-5 lines thick, the convex rim protruding as a thick rim.—E. Bosistoana, F. v. M. Next to E. pilularis in the key but perhaps related to E. melliodora. Lvs. narrow-lanceolate, copiously dotted, of equal color on both sides; veins very divergent: fls. few and pedicelled in the umbels: peduncles somewhat compressed; lid fully as long as tube, narrow-hemispheric: fr. small, with narrow rim; valves inclosed. Maiden, Crit. Rev. Eucal. 49 (figs. 1-1).—E. californica, used by Abbot Kinney in his book entitled "Eucalyptus," has not been recognized by botanists: also listed as E. occidentalis var. Californica, Kinney.—E. cinirea, F. v. M. Related to E. viminalis. Bark persistent, fibrous: Lvs. opposite. sessile, cordate, more or less white-mealy: fls. 3-7, pedicellate: fr. 3 lines thick, with protruding valves.—E. dealbata, A. Cunn. Small tree, near E. viminalis: Lvs. glaucous, often broad and obtuse: fls. 3-6, small: fr.-rim flat; valves protruding even before they open. Cult. in Cuba.—E. Deanei, Maiden, very close to E. saligna: distinguished chiefly by its broad sucker Lvs.—E. Foeld Bay (?), Naudin, is a horticultural form either of E. rostrata or of E. tereticornis: branchlets pendulous.—E. jugalis, Naudin, is a cult. form not yet identified. —E. Maidenii, F.v.M. Appearance and bark of E. goniocalyx but peculiar warty buds and caps of E. globulus: branchlets quadrangular.—E. McClatchie, Kinney, is a horticultural name for the large-fld. form of E. Gunnii var. acervula.—E. miniata, A. Cunn. Placed after E. ficifolia in the key: fls. sessile in simple umbels, brilliant orange-color: fr. truncate-ovate, nearly 2 in. long. F.v.M. Eucal. 6:4.—E. Mortoniana, Kinney. is a horticultural species probably referable to E. Maideni. Maiden, Crit. Rev. Eucal. 79 (figs. 13-14); 80 (figs. 1-12).—E. patens. Benth. Next to E. pilularis in the key: peduncles only slightly flattened, bearing 3-7 fls.: lid hemispherical, short-pointed, about half as long as tube: fr. truncate-ovate, 5 lines wide; rim narrow; caps. sunk. F.v.M. Eucal. 9:5.—E. phaceafolia, listed by Richter in Calif. Exp. Sta. Bull. No. 217, p. 1011, is probably a misprint for E. ficifolia.—E. pinnata, a garden name. J. U. Maiden suggests that Californian specimens under this name may be E. coccifera (Crit. Rev. Eucal., p. 143).—E. rubida, Deane & Maiden. Characters of E. viminalis. but bark always smooth and white, often with reddish patches, and the sucker lvs. broad.—E. uncinata, Turcz. Near E. decipiens in the key and, like it, a shrub: bark deciduous, smooth: Lvs. very light green, narrow, copiously dark- dotted; veins fine, widely divergent: filaments kinked; anthers opening by terminal pores: fr. 2-3 lines across; valves little if at all exserted. F.v.M. Eucal. 4:10. Maiden, Crit. Rev. Eucal. 62. —E. urnigera. Hook. f. Shapely tree with drooping branchlets and glaucous bluish foliage: bark smooth, pale brown: Lvs. 2-4 in. long, obtuse: fls. mostly 3 in each umbel; peduncles often recurved: fr. nearly globose but somewhat urn-shaped, 4-5 lines wide: caps. much sunk and valves inclosed. Maiden Crit. Rev. Eucal. 80 (Figs. 13-15). Other names offered in foreign catalogues are: E. capitellata, E. consideneana, E. delegatensis, E. divas, E. gonipho-cornuta, B loxophleba, E. paludosa, E. Smithii. Harvey Monroe Hall. The above text is from the Standard Cyclopedia of Horticulture. It may be out of date, but still contains valuable and interesting information which can be incorporated into the remainder of the article. Click on "Collapse" in the header to hide this text.

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? Eucalyptus
Eucalyptus melliodora foliage and flowers
Plant Info
Scientific classification
Kingdom: Plantae Division: Magnoliophyta Class: Magnoliopsida Order: Myrtales Family: Myrtaceae Genus: Eucalyptus L'Hér.
Species
About 700; see the List of Eucalyptus species
natural range

Eucalyptus (From Greek, ευκάλυπτος = "Well covered") is a diverse genus of trees (and a few shrubs), the members of which dominate the tree flora of Australia. There are more than seven hundred species of Eucalyptus, mostly native to Australia, with a very small number found in adjacent parts of New Guinea and Indonesia and one as far north as the Philippine islands.

Members of the genus can be found in almost every region of the Australian continent, because they have adapted to all of its climatic conditions; in fact no other continent is so characterised by a single genus of tree as Australia is by its eucalyptus. Many, but far from all, are known as gum trees in reference to the habit of many species to exude copious sap from any break in the bark (e.g. Scribbly Gum).

Description

Eucalyptus regnans, a forest tree, showing crown dimension, Tasmania, Australia

Eucalyptus camaldulensis, immature, woodland trees, showing collective crown habit, Murray River, Tocumwal, New South Wales, Australia

Eucalyptus cretata, juvenile, showing low branching ‘mallee’ form, Melbourne, Victoria, Australia

Eucalyptus angustissima, showing shrub form, Melbourne, Victoria, Australia

Eucalyptus platypus, showing ‘Marlock’ form, Melbourne

Size and habit

A Eucalyptus may be mature as a low shrub or as a very large tree. There are three main habit and four size categories that species can be divided into.

As a generalisation "forest trees" are single-stemmed and have a crown forming a minor proportion of the whole tree height. "Woodland trees" are single-stemmed although they may branch at a short distance above ground level.

"Mallees" are multi-stemmed from ground level, usually less than 10 metres in height, often with the crown predominantly at the ends of the branchlets and individual plants may combine to form either an open or closed formation. Many mallee trees may be so low growing as to be considered a shrub.

Apart from the forest tree, woodland tree, mallee and shrub habits two further tree forms are notable in Western Australia. One of these is the "mallet", which is a small to medium-sized tree, usually of steep branching habit, sometimes fluted at the base of the trunk and often with a conspicuously dense, terminal crown. It is the habit usually of mature healthy specimens of Eucalyptus occidentalis, E. astringens, E. spathulata, E. gardneri, E. dielsii, E. forrestiana, E. salubris, E. clivicola and E. ornata. The smooth bark of mallets often has a satiny sheen and may be white, cream, grey, green or copper.

Another habit category used in Western Australia is the "marlock". This has been variously applied but Brooker & Hopper (2001) defined the term and restricted the use to describe the more or less pure stands of short, erect, thin-stemmed "trees" that do not produce lignotubers. These are easily seen and recognised in stands of E. platypus, E. vesiculosa and the unrealted E. stoatei. The marlock is distinguished from mallets which are taller and have a characteristic steep branching habit. The origin and use of the term "morrel" is somewhat obscure and appears to apply to trees of the western Australian wheatbelt and goldfields which have a long, straight trunk, completely rough barked. It is now used mainly for E. longicornis (Red Morell) and E. melanoxylon (Black Morrel).

Tree sizes follow the convention of:

• Small - to 10 metres in height
• Medium sized - 10 to 30 metres in height
• Tall - 30 to 60 metres in height
• Very Tall - over 60 metres in height

Leaves

Nearly all Eucalyptus are evergreen but some tropical species lose their leaves at the end of the dry season. As in other members of the Myrtle family, Eucalyptus leaves are covered with oil glands. The copious oils produced are an important feature of the genus.

Eucalyptus tetragona, showing glaucous leaves & stems

The leaves on a mature Eucalyptus plant are commonly lanceolate, petiolate, apparently alternate and waxy or glossy green. In contrast the leaves of seedlings are frequently opposite, sessile and glaucous. However there are numerous exceptions to this pattern. Many species such as E. melanophloia and E. setosa retain the juvenile leaf form even when the plant is reproductively mature. Some species such as E. macrocarpa, E. rhodantha and E. crucis are sought after ornamentals due to this lifelong juvenile leaf form. A few species such as E. petraea, E. dundasii and E. lansdowneana have shiny green leaves throughout their life cycle. E. caesia exhibits the opposite pattern of leaf development to most Eucalyptus, with shiny green leaves in the seedling stage and dull, glaucous leaves in mature crowns. The contrast between juvenile and adult leaf phases is valuable in field identification.

Four leaf phases are recognised in the development of a Eucalyptus plant - the ‘seedling’, ‘juvenile’, ‘intermediate’ and ‘adult’ phases. However there is no definite transitional point between the phases. The intermediate phase, when the largest leaves are often formed, links the juvenile and adult phases. Most species do not flower until adult foliage starts to appear; E. cinerea and E. perriniana are notable exceptions.

In all except a few species the leaves form in pairs on opposite sides of a square stem, consecutive pairs being at right angles to each other (decussate). In some narrow-leaved species - for example E. oleosa - the seedling leaves after the second leaf pair are often clustered in a detectable spiral arrangement about a five sided stem. After the spiral phase, which may last from several to many nodes, the arrangement reverts to decussate by the absorption of some of the leaf bearing faces of the stem. In those species with opposite adult foliage the leaf pairs, which have been formed opposite at the stem apex, become separated at their bases by unequal elongation of the stem to produce the apparently alternate adult leaves.

Eucalyptus leucoxylon var. ‘Rosea’ showing flowers & buds with operculum present

Eucalyptus sideroxylon, showing fruit (capsules) & buds with operculum present.

Flowers

The most readily recognisable characteristics of Eucalyptus species are its distinctive flowers and fruit (capsule). Flowers have numerous fluffy stamens which may be white, cream, yellow, pink or red; in bud the stamens are enclosed in a cap known as an operculum which is composed of the fused sepals or petals or both. Thus flowers have no petals, decorating themselves instead with the many showy stamens. As the stamens expand the operculum is forced off, splitting away from the cup-like base of the flower; this is one of the features that that unites the genus. The name Eucalyptus, from the Greek words eu-, well, and kaluptos, cover, meaning "well-covered", describes the operculum. The woody fruits or capsules, known as gumnuts, are roughly cone-shaped and have valves at the end which open to release the seeds. Most species do not flower until adult foliage starts to appear; Eucalyptus cinerea and Eucalyptus perriniana are notable exceptions.

Eucalyptus sp in East Gippsland, Victoria, Australia, showing ‘ribbon’ bark form.

The dark, fissured ‘Ironbark’ bark of Eucalyptus sideroxylon

Bark

The appearance of Eucalyptus bark will vary with the age of the plant, the manner of bark shed, the length of the bark fibres, the degree of furrowing, the thickness, the hardness and the colour. All mature eucalypts put on an annual layer of bark, which contributes to the increasing diameter of the stems. In some species the outermost layer dies and is annually deciduous either in long strips (as in Eucalyptus sheathiana) or in variably sized flakes (Eucalyptus diversicolor, Eucalyptus cosmophylla or Eucalyptus cladocalyx). These are the gums or smooth-barked species. The gum bark may be dull, shiny or satiny (as in Eucalyptus ornata) or matt (Eucalyptus cosmophylla). In many species the dead bark is retained. Its outermost layer gradually fragments with weathering and sheds without altering the essentially rough barked nature of the trunks or stems - for example Eucalyptus marginata, Eucalyptus jacksonii, Eucalyptus obliqua and Eucalyptus porosa.

The extraordinary coloured bark of Eucalyptus deglupta native to South East Asia

Many species are ‘half-barks’ or ‘blackbutts’ in which the dead bark is retained in the lower half of the trunks or stems - for example, Eucalyptus brachycalyx, Eucalyptus ochrophloia and Eucalyptus occidentalis - or only in a thick, black accumulation at the base, as in Eucalyptus clelandii. Some species in this category - for example - Eucalyptus youngiana - the rough basal bark is very ribbony at the top, where it gives way to the smooth upper stems. The smooth upper bark of the half barks and that of the completely smooth-barked trees and mallees can produce remarkable colour and interest, for example Eucalyptus deglupta.

The box bark of Eucalyptus quadrangulata, or White Box

Bark characteristics

• Stringybark - consists of long-fibres and can be pulled off in long pieces. It is usually thick with a spongy texture.
• Ironbark - is hard, rough and deeply furrowed. It is impregnated with dried kino (a sap exuded by the tree) which gives a dark red or even black colour.
• Tessellated - bark is broken up into many distinct flakes. They are corkish and can flake off.
• Box - has short fibres. Some also show tessellation.
• Ribbon - this has the bark coming off in long thin pieces but still loosely attached in some places. They can be long ribbons, firmer strips or twisted curls.

Species and hybridism

There are over 700 species of Eucalyptus; refer to the List of Eucalyptus species for a comprehensive list of species. It is believed that all eucalypts are related either closely or remotely. Some have diverged from the mainstream of the genus to the extent that they are quite isolated genetically and are able to be recognised by only a few relatively invariant characteristics. Most, however, may be regarded as belonging to large or small groups of related species, which are often in geographical contact with each other and between which gene exchange still occurs. In these situations many species will appear to grade into one another and intermediate forms are common. In other words, some species are relatively fixed genetically, as expressed in their morphology, while others have not diverged completely from their nearest relatives.

Hybrid individuals have not always been recognised as such on first collection and some have been named as new species, such as E. chrysantha (E. preissiana × E. sepulcralis) and E. "rivalis" (E. marginata × E. megacarpa). Hybrid combinations are not particularly common in the field, but some other published species have been suggested to be hybrid combinations and are frequently seen in Australia. For example, E. erythrandra is believed to be E. angulosa × E. teraptera and due to its wide distribution is often referred to in texts.

Related genera

A small genus of similar trees, Angophora, has also been known since the 18th century. In 1995 new evidence, largely genetic, indicated that some prominent Eucalyptus species were actually more closely related to Angophora than to the other eucalypts; they were split off into the new genus Corymbia. Although separate, the three groups are allied and it remains acceptable to refer to the members of all three genera Angophora, Corymbia and Eucalyptus as "eucalypts". The coolibah trees, referred to in Waltzing Matilda, are Eucalyptus E. coolabah and E. microtheca.

Eucalyptus regnans exceeding 80 metres, in an area of extensive logging, Tasmania

Tall timber

Today, specimens of the Australian Mountain Ash, Eucalyptus regnans, are among the tallest trees in the world at up to 92 metres in height and the tallest of all flowering plants (Angiosperms); taller trees such as the Coast Redwood are all conifers (Gymnosperms). There is credible evidence however that at the time of European settlement of Australia some Mountain Ash were indeed the tallest plants in the world.

Tolerance

Most eucalypts are not tolerant of frost, or only tolerate light frosts down to -3°C to -5°C; the hardiest, are the so-called Snow Gums such as Eucalyptus pauciflora which is capable of withstanding cold and frost down to about -20°C. Two sub-species, E. pauciflora subsp. niphophila and E. pauciflora subsp. debeuzevillei in particular are even hardier and can tolerate even quite severe winters. Several other species, especially from the high plateau and mountains of central Tasmania such as Eucalyptus coccifera, Eucalyptus subcrenulata, and Eucalyptus gunnii, have produced extreme cold hardy forms and it is seed procured from these genetically hardy strains that are planted for ornament in colder parts of the world.

Animal relationships

Phascolarctos cinereus Koala eating eucalyptus leaves

An essential oil extracted from eucalyptus leaves contains compounds that are powerful natural disinfectants and which can be toxic in large quantities. Several marsupial herbivores, notably koalas and some possums, are relatively tolerant of it. The close correlation of these oils with other more potent toxins called formylated phloroglucinol compounds allows koalas and other marsupial species to make food choices based on the smell of the leaves. However, it is the formylated phloroglucinol compounds that are the most important factor in choice of leaves by koalas. Eucalyptus flowers produce a great abundance of nectar, providing food for many pollinators including insects, birds, bats and possums. Despite the fact that eucalyptus trees are well-defended from herbivores by their toxic essential oils they do have their share of insect pests, such as the Eucalyptus Longhorn Borer Beetle, Phoracantha semipunctuata, or the aphid-like psyllids known as "bell lerps," both of which have become established as pests throughout the world wherever eucalypts are cultivated.

Hazards

A fallen log is embedded in a Eucalyptus albens. This formation is the tree's response.

Some species of Eucalyptus have a habit of dropping entire branches off as they grow. Eucalyptus forests are littered with dead branches. The Australian Ghost Gum Eucalyptus papuana is also termed the "widow maker," due to the high number of pioneer tree-felling workers who were killed by falling branches. Many people have been killed as they camped underneath the trees. It is thought the trees shed very large branches to conserve water during periods of drought. This may be the real reason behind the drop bear story told to children - the idea is to keep them away from being under dangerous branches.

Fire

On warm days vapourised eucalyptus oil rises above the bush to create the characteristic distant blue haze of the Australian landscape. Eucalyptus oil is highly flammable (trees have been known to explode) and bush fires can travel easily through the oil-rich air of the tree crowns. The dead bark and fallen branches are also flammable. Eucalypts are well adapted for periodic fires, in fact most species are dependent on them for spread and regeneration. Template:Fact They do this via lignotubers, epicormic buds under the bark and from fire-germinated seeds sprouting in the ashes. Template:Fact

Eucalyptus forest in a state of regeneration

Eucalypts originated between 35 and 50 million years ago, not long after Australia-New Guinea separated from Gondwana, their rise coinciding with an increase in fossil charcoal deposits (suggesting that fire was a factor even then), but they remained a minor component of the Tertiary rainforest until about 20 million years ago when the gradual drying of the continent and depletion of soil nutrients led to the development of a more open forest type, predominantly Casuarina and Acacia species. With the arrival of the first humans about 50 thousand years ago fires became much more frequent and the fire-loving eucalypts soon came to account for roughly 70% of Australian forest.

Eucalypts regenerate quickly after fire. After the Canberra bushfires of 2003, hectares of imported species were killed, but in a matter of weeks the gum trees were putting out suckers and looking generally healthy. Template:Fact

The two valuable timber trees, Alpine Ash E. delegatensis and Mountain Ash E. regnans, are killed by fire and only regenerate from seed. The same 2003 bushfire that had little impact on forests around Canberra resulted in thousands of hectares of dead ash forests. However, a small amount of ash survived and put out new suckers as well. There has been some debate as to whether to leave the stands, or attempt to harvest the mostly undamaged timber, which is increasingly recognised as a damaging practice.

Cultivation and uses

Eucalyptus niphophila in Namadgi National Park

Eucalyptus have many uses which have made them economically important trees. Perhaps the Karri and the Yellow box varieties are the best known. Due to their fast growth the foremost benefit of these trees is the wood. They provide many desirable characteristics for use as ornament, timber, firewood and pulpwood. Fast growth also makes eucalypts suitable as windbreaks. Eucalypts draw a tremendous amount of water from the soil through the process of transpiration. They have been planted (or re-planted) in some places to lower the water table and reduce soil salination. Eucalypts have also been used as a way of reducing malaria by draining the soil in Algeria, Sicily and also in Europe and California. Drainage removes swamps which provide a habitat for mosquito larvae, but such drainage can also destroy ecologically productive areas.

Eucalyptus oil is readily steam distilled from the leaves and can be used for cleaning, deodorising, and in very small quantities in food supplements; especially sweets, cough drops and decongestants. Eucalyptus oil has insect repellent properties (Jahn 1991 a, b; 1992), and is an active ingredient in some commercial mosquito repellents (Fradin & Day 2002).

The nectar of some eucalyptus produces high quality monofloral honey. The ghost gum's leaves were used by Aborigines to catch fish. Soaking the leaves in water releases a mild tranquilliser which stuns fish temporarily. Eucalyptus is also used to make the digeridoo, a musical wind instrument made popular by the Aborigines of Australia.

All parts of the eucalyptus may be used to make plant dyes that are substantive on protein fibres (silk and wool) simply by processing the plant part with waterTemplate:Fact. Colours to be achieved range from yellow and orange through green, tan, chocolate and deep rust red. The material remaining after processing can be safely used as mulchTemplate:Fact.

History

Sir Joseph Banks

Although Eucalypts must have been seen by the very early European explorers and collectors, no botanical collections of them are known to have been made until 1770 when Joseph Banks and Daniel Solander arrived at Botany Bay with Captain James Cook. There they collected specimens of E. gummifera and later, near the Endeavour River in northern Queensland, they collected E. platyphylla; neither of these species was named as such at the time.

In 1777, on Cook's third expedition, David Nelson collected a eucalypt on Bruny Island in southern Tasmania. This specimen was taken to the British Museum in London, and it was named Eucalyptus obliqua by the French botanist L'Héritier, who was working in London at the time. He coined the generic name from the Greek roots eu and calyptos, meaning "well" and "covered" in reference to the operculum of the flower bud. This organ protects the developing flower parts as the flower develops and is shed by the pressure of the emerging stamens at flowering.

The name obliqua was derived from the Latin obliquus, meaning "oblique" which is the botanical term describing a leaf base where the two sides of the leaf blade are of unequal length and do not meet the petiole at the same place.

In naming E. obliqua, L'Héritier caused to be perpetuated, most likely by accident, a feature common to all eucalypts - the operculum. In his choice of a specific name, he recognised not only the characteristic feature of E. obliqua, but one common to many other species as well. E. obliqua was published in 1788-89 and coincides with the date of the first official European settlement of Australia.

Ferdinand von Mueller

Between 1788-89 and the turn of the nineteenth century several more species of Eucalyptus were named and published. Most of these were by the English botanist James Edward Smith and most were, as might be expected, trees of the Sydney region. These include the economically valuable E. pilularis, E. saligna and E. tereticornis.

The nineteenth century saw the endeavours of several of the great botanists in Australian history, particularly Ferdinand von Mueller, whose work on eucalypts contributed greatly to the first comprehensive account of the genus in George Bentham's Flora Australiensis in 1867 - which today remains the only complete Australian flora. The account in Bentham is the most important early systematic treatment of the genus. Bentham divided the genus into five series whose distinctions were based on characteristics of the stamens, particularly the anthers (Mueller, 1879-84), elborated further by Joseph Henry Maiden (1903-33), and taken even further by William Faris Blakely (1934). By this time the anther system had become too complex to be workable and more recent systematic work has concentrated on the characteristics of buds, fruits, leaves and bark.

The first endemic Western Australian Eucalyptus to be collected and subsequently named was the yate (E. cornuta) by the French botanist La Billardiére, who collected in what is now the Esperance area in 1792.

Plantation and ecological problems

Eucalyptus was first introduced to the rest of the world by Sir Joseph Banks, botanist, on the Cook expedition in 1770. They have subsequently been introduced to many parts of the world, notably California, Brazil, Ecuador, Colombia, Ethiopia, Morocco, Portugal, South Africa, Israel, Galicia and Chile. In Spain they have been planted in pulpwood plantations, replacing native oak woodland. Eucalyptus are the basis for several industries, such as sawmilling, pulp, charcoal and others. Several species have become invasive and are causing major problems for local ecosystems.

California

In the 1850s many Australians traveled to California to take part in the California Gold Rush. Much of California has a similar climate to parts of Australia and some people got the idea of introducing eucalypts. By the early 1900s thousands of acres of eucalypts were planted with the encouragement of the state government. It was hoped that they would provide a renewable source of timber for construction and furniture making. However, this did not happen, partly because the trees were cut when they were too young and partly because the Americans did not know how to process the cut trees to prevent the wood from twisting and splitting.

One way in which the eucalyptus, mainly the blue gum E. globulus, proved valuable in California was in providing windbreaks for highways, orange groves, and other farms in the mostly treeless central part of the state. They are also admired as shade and ornamental trees in many cities and gardens.

Eucalyptus forests in California have been criticized because they compete with native plants and do not support native animals. Fire is also a problem. The 1991 Oakland Hills firestorm which destroyed almost 3,000 homes and killed 25 people was partly fueled by large numbers of eucalypts in the area close to the houses.

In some parts of California eucalypt forests are being removed and native trees and plants restored. Individuals have also illegally destroyed some trees and are suspected of introducing insect pests from Australia which attack the trees.

Brazil

In 1910 Eucalyptus was introduced to Brazil for timber substitution and the vegetal coal industry. It has adpated very well to the local environmental conditionsTemplate:Fact and today there are around 5 million hectares planted. The wood produced by the tree is highly appreciated by the charcoal and pulp and paper industries. The short rotation allows a larger wood production and supply wood for several other activities, helping to preserve the native forests from logging. When well managed the plantations are sustainable and the soil can sustain endless replantations. Eucalyptus plantations are also used as wind breaks.

Ethiopia

This species was introduced to Ethiopia in either 1894 or 1895, either by Emperor Menelik II's French advisor Mondon-Vidailhet or the Englishman Captain O'Brian. Due to massive deforestation around his new capital city Addis Ababa caused by a growing appetite for fire wood, Emperor Menelik II endorsed its planting around that city; according to Richard R.K. Pankhurst, "The great advantage of the eucalypts was that they were fast growing, required little attention and when cut down grew up again from the roots; it could be harvested every ten years. The tree proved successful from the onset". Plantations of eucalypts spread from the capital to other growing urban centers such as Debre Marqos; Pankhurst reports that the most common species found in Addis Ababa in the mid-1960s was E. globulus, although he also found E. melliodora and E. rostrata in significant numbers. David Buxton, writing of central Ethiopia in the mid-1940s, observed that eucalyptus trees "have become an integral -- and a pleasing -- element in the Shoan landscape and has largely displaced the slow-growing native 'cedar' or juniper."

Popular opposition soon developed that in 1913 a proclamation was issued ordering a partial destruction of all standing trees, and their replacement with mulberry trees. "The proclamation," Pankhurst notes, "however remained a dead letter; there is no evidence of eucalypts being uprooted, still less of mulberry trees being planted." The eucalypt remains a defining feature of Addis Ababa.

Photo gallery

• Eucalyptus forest.jpg

  Eucalyptus forest in East Gippsland, Victoria. Mostly Eucalyptus albens (white box).

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  Eucalyptus forest in East Gippsland, Victoria. Mostly Eucalyptus albens (white box).

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  Eucalyptus forest in East Gippsland, Victoria. Mostly Eucalyptus albens (white box).

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  A eucalyptus tree with the sun shining through its branches.

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  Eucalyptus bridgesiana (Apple box) on Red Hill, Australian Capital Territory.

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  Eucalyptus gunnii planted in southern England. The lower part of the trunk is covered in ivy.

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  Eucalyptus cinerea x pulverulenta - National Botanical Gardens Canberra

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  Eucalyptus Pink Waxy Scale Insects

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  Eucalyptus grandis. Province of Buenos Aires, Argentina.

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  Eucalyptus plantation in Galicia in Northwest Spain

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  Eucalyptus rubida (Candlebark gum) in Burra, New South Wales.

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  This tree in Heathcote National Park has a serious problem.

References

• Brooker, M.I.H.; Kleinig, D.A. (2001). Field Guide to Eucalyptus. Melbourne: Bloomings. 
• Pankhurst, Richard (1968). Economic History of Ethiopia. Addis Ababa: Haile Selassie I University. 

External links

• EUCLID Sample, CSIRO
• The Eucalyptus Page
• EucaLink
• Currency Creek Arboretum - Eucalypt Research
• Eucalyptus globulus Diagnostic photos: tree, leaves, bark
• Handbook of Energy Crops Duke, James A. 1983.
• The Eucalyptus of Califonia: Seeds of Good or Seeds of Evil? Santos, Robert. 1997 Denair, CA : Alley-Cass Publications
• Impacts of Monoculture: The Case of Eucalyptus Plantations in Thailand a paper for the Monocultures: Environmental and Social Effects and Sustainable Alternatives Conference, June 2-6 1996, Songkhla, Thailand, prepared by Areerat Kittisiri, Rural Reconstruction and Friends Association (RRAFA), Bangkok, Thailand

Medicinal resources, eucalyptus essential oil

• http://www.botanical.com/botanical/mgmh/e/eucaly14.html
• http://www.henriettesherbal.com/eclectic/bpc1911/eucalyptus_oleu.html