Eucalyptus

Eucalyptus
Eucalyptus tereticornis flowers, capsules, buds and foliage.jpeg
Buds, capsules, flowers and foliage of E. tereticornis
Scientific classification e
Kingdom: Plantae
Clade: Angiosperms
Clade: Eudicots
Clade: Rosids
Order: Myrtales
Family: Myrtaceae
Subfamily: Myrtoideae
Tribe: Eucalypteae
Genus: Eucalyptus
L'Hér.
Type species
Eucalyptus obliqua
L'Hér. 1789
Diversity
about 700 species
Distribution.eucalyptus.png
Natural range
Synonyms [1]

Aromadendron Andrews ex Steud.
Eucalypton St.-Lag.
Eudesmia R.Br.
Symphyomyrtus Schauer

Eucalyptus s/ [2] L'Héritier 1789 [3] is a diverse genus of flowering trees and shrubs (including a distinct group with a multiple-stem mallee growth habit) in the myrtle family, Myrtaceae. Members of the genus dominate the tree flora of Australia, and include Eucalyptus regnans, the tallest known flowering plant on Earth. [4] There are more than 700 species of eucalyptus and most are native to Australia; a very small number are found in adjacent areas of New Guinea and Indonesia. One species, Eucalyptus deglupta, ranges as far north as the Philippines. Of the 15 species found outside Australia, just nine are exclusively non-Australian. Species of eucalyptus are cultivated widely in the tropical and temperate world, including the Americas, Europe, Africa, the Mediterranean Basin, the Middle East, China, and the Indian subcontinent. However, the range over which many eucalypts can be planted in the temperate zone is constrained by their limited cold tolerance. [5] Australia is covered by 92,000,000 hectares (227,336,951 acres) of eucalypt forest, comprising three quarters of the area covered by native forest. [6]

Eucalyptus is one of three similar genera that are commonly referred to as " eucalypts", the others being Corymbia and Angophora. Many species, though by no means all, are known as gum trees because they exude copious kino from any break in the bark (e.g., scribbly gum). The generic name is derived from the Greek words ευ (eu) "well" and καλύπτω (kalýpto) "to cover", referring to the operculum on the calyx that initially conceals the flower. [7]

Some eucalyptus species have attracted attention from horticulturists, global development researchers, and environmentalists because of desirable traits such as being fast-growing sources of wood, producing oil that can be used for cleaning and as a natural insecticide, or an ability to be used to drain swamps and thereby reduce the risk of malaria. Eucalyptus oil finds many uses like in fuels, fragrances, insect repellance and antimicrobial activity. Eucalyptus trees show allelopathic effects; they release compounds which inhibit other plant species from growing nearby. Outside their natural ranges, eucalypts are both lauded for their beneficial economic impact on poor populations [8] [9]:22 and criticised for being "water-guzzling" aliens, [10] leading to controversy over their total impact. [11]

On warm days, eucalyptus forests are sometimes shrouded in a smog-like mist of vaporised volatile organic compounds ( terpenoids); the Australian Blue Mountains take their name from the haze. [12]

Description

Eucalyptus regnans, a forest tree, showing crown dimension, Tasmania
Eucalyptus camaldulensis, immature woodland trees, showing collective crown habit, Murray River, Tocumwal, New South Wales
Eucalyptus cretata, juvenile, showing low branching 'mallee' form, Melbourne, Victoria
Eucalyptus angustissima, showing shrub form, Melbourne
Eucalyptus platypus, showing ‘marlock’ form, Melbourne

Size and habit

A mature eucalyptus may take the form of a low shrub or a very large tree. The species can be divided into three main habits and four size categories.

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 multistemmed from ground level, usually less than 10 m (33 ft) 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.

Two other tree forms are notable in Western Australia and described using the native names "mallet" and "marlock". The " mallet" is a small to medium-sized tree that does not produce lignotubers and has a relatively long trunk, a steeply branching habit and often a conspicuously dense terminal crown. This is the normal habit 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.

The term marlock has been variously used; in Forest Trees of Australia, it is defined as a small tree without lignotubers, but with a shorter, lower-branching trunk than a mallet. They usually grow in more or less pure stands. Clearly recognisable examples are stands of E. platypus, E. vesiculosa, and the unrelated E. stoatei.

The term "morrell" is somewhat obscure in origin 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 morrell) and E. melanoxylon (black morrell).

Tree sizes follow the convention of:

  • Small: to 10 m (33 ft) in height
  • Medium-sized: 10–30 m (33–98 ft)
  • Tall: 30–60 m (98–197 ft)
  • Very tall: over 60 m (200 ft)

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. Although mature eucalyptus trees may be towering and fully leafed, their shade is characteristically patchy because the leaves usually hang downwards.

Eucalyptus tetragona, showing glaucous leaves and 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 often opposite, sessile and glaucous, but many exceptions to this pattern exist. 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, no definite transitional point occurs between the phases. The intermediate phase, when the largest leaves are often formed, links the juvenile and adult phases. [13]

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 and buds with operculum present
Eucalyptus melliodora, showing flowers and opercula

Flowers

The most readily recognisable characteristics of eucalyptus species are the distinctive flowers and fruit (capsules or "gumnuts"). 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, but instead decorate themselves 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 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 are roughly cone-shaped and have valves at the end which open to release the seeds, which are waxy, rod-shaped, about 1 mm in length, and yellow-brown in colour. Most species do not flower until adult foliage starts to appear; E. cinerea and E. perriniana are notable exceptions.

The dark, fissured ' ironbark' of E. sideroxylon

Bark

Bark detail of E. angophoroides, the apple box
The extraordinary coloured bark of E. deglupta native to Southeast Asia
The 'box' bark of E. quadrangulata, the white box

The appearance of eucalyptus bark varies 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 E. sheathiana) or in variably sized flakes ( E. diversicolor, E. cosmophylla, or E. cladocalyx). These are the gums or smooth-barked species. The gum bark may be dull, shiny, or satiny (as in E. ornata) or matte ( E. 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 E. marginata, E. jacksonii, E. obliqua, and E. porosa.

E. globulus bark cells are able to photosynthesize in the absence of foliage, conferring an "increased capacity to re-fix internal CO2 following partial defoliation". [14] This allows the tree to grow in less-than-ideal climates, in addition to providing a better chance of recovery from damage sustained to its leaves in an event such as a fire. [15]

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, E. brachycalyx, E. ochrophloia, and E. occidentalis — or only in a thick, black accumulation at the base, as in E. clelandii. In some species in this category, for example E. youngiana and E. viminalis, 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 E. deglupta. [13]

Different commonly recognised types of bark include:

  • 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 — has the bark coming off in long, thin pieces, but is still loosely attached in some places. They can be long ribbons, firmer strips, or twisted curls.
Other Languages
Afrikaans: Eucalyptus
አማርኛ: ባህር ዛፍ
Аҧсшәа: Аевкалипт
العربية: أوكالبتوس
Avañe'ẽ: Eukalíto
azərbaycanca: Evkalipt
беларуская: Эўкаліпт
беларуская (тарашкевіца)‎: Эўкаліпт
български: Евкалипт
bosanski: Eukaliptus
català: Eucaliptus
Cebuano: Eucalyptus
čeština: Blahovičník
Cymraeg: Ewcalyptws
dansk: Eukalyptus
Deutsch: Eukalypten
Diné bizaad: Akʼah sisíʼí tsin
eesti: Eukalüpt
Ελληνικά: Ευκάλυπτος
español: Eucalyptus
Esperanto: Eŭkalipto
euskara: Eukalipto
فارسی: اکالیپتوس
français: Eucalyptus
Gaeilge: Eoclaip
Gaelg: Eucalyptus
galego: Eucalipto
ગુજરાતી: નીલગિરી
Հայերեն: Նվենի
hornjoserbsce: Eukalyptowc
hrvatski: Eukaliptus
Bahasa Indonesia: Eukaliptus
italiano: Eucalyptus
עברית: אקליפטוס
ಕನ್ನಡ: ನೀಲಗಿರಿ
ქართული: ევკალიპტი
қазақша: Эвкалипт
Kiswahili: Mkalatusi
Kurdî: Okalîptûs
Кыргызча: Эвкалипт
кырык мары: Эвкалипт
Latina: Eucalyptus
latviešu: Eikalipti
lietuvių: Eukaliptas
magyar: Eukaliptusz
မြန်မာဘာသာ: ယူကလစ်တပ်ပင်
Nederlands: Eucalyptus
日本語: ユーカリ
occitan: Eucalyptus
پنجابی: یوکلپٹس
polski: Eukaliptus
português: Eucalyptus
română: Eucalipt
Runa Simi: Kalistu
русский: Эвкалипт
sardu: Eucalyptus
Scots: Eucalyptus
Simple English: Eucalyptus
slovenčina: Eukalyptus
slovenščina: Evkalipt
српски / srpski: Еукалиптус
srpskohrvatski / српскохрватски: Eukaliptus
Tagalog: Eukaliptus
తెలుగు: యూకలిప్టస్
lea faka-Tonga: Pulukamu
Türkçe: Okaliptüs
українська: Евкаліпт
اردو: یوکلپٹس
Tiếng Việt: Bạch đàn
Winaray: Eucalyptus
粵語: 尤加利
中文: 桉树