Eucalyptus

Seeds of Eucalyptus camaldulensis
  E. tetragona, showing glaucous leaves and stems
Size and habitEdit
Eucalypts vary in size and habit from shrubs to tall trees. Trees usually have a single main stem or trunk but many eucalypts are mallees that are multistemmed from ground level and rarely taller than 10 metres (33 ft). There is no clear distinction between a mallee and a shrub but in eucalypts, a shrub is a mature plant less than 1 metre (3 ft) tall and growing in an extreme environment. E. vernicosa in the Tasmanian highlands, E. yalatensis on the Nullarbor and E. surgens growing on coastal cliffs in Western Australia are examples of eucalypt shrubs.The terms "mallet" and "marlock" are only applied to Western Australian eucalypts. A mallet is a tree with a single thin trunk with a steeply branching habit but lacks both a lignotuber and epicormic buds. E. astringens is an example of a mallet. A marlock is a shrub or small tree with a single, short trunk, that lacks a lignotuber and has spreading, densely leafy branches that often reach almost to the ground. E. platypus is an example of a marlock.Eucalyptus trees, including mallees and marlocks, are single-stemmed and include Eucalyptus regnans, the tallest known flowering plant on Earth.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)
 

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




 

E. camaldulensis, immature woodland trees, showing collective crown habit, Murray River, Tocumwal, New South Wales




 

E. cretata, juvenile, showing low branching 'mallee' form, Melbourne, Victoria




 

E. angustissima, showing shrub form, Melbourne




 

E. platypus, showing ‘marlock’ form, Melbourne



BarkEdit
All eucalypts add a layer of bark every year and the outermost layer dies. In about half of the species, the dead bark is shed exposing a new layer of fresh, living bark. The dead bark may be shed in large slabs, in ribbons or in small flakes. These species are known as "smooth barks" and include E. sheathiana, E. diversicolor, E. cosmophylla and E. cladocalyx. The remaining species retain the dead bark which dries out and accumulates. In some of these species, the fibres in the bark are loosely intertwined (in stringybarks such as E. macrorhyncha or peppermints such as E. radiata) or more tightly adherent (as in the "boxes" such as E. leptophleba). In some species (the "ironbarks" such as E. crebra and E. jensenii) the rough bark is infused with gum resin.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.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". 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.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.
 

Bark detail of E. angophoroides, the apple-topped box




 

The extraordinary coloured bark of E. deglupta native to Southeast Asia




 

The 'box' bark of E. quadrangulata, the white-topped box




 

The dark, fissured 'ironbark' of E. sideroxylon



LeavesEdit
  Eucalyptus leucoxylon var. 'Rosea' showing flowers and buds with operculum present
  Eucalyptus melliodora, showing flowers and opercula
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.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.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.
FlowersEdit
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 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.

3-6 hours of sun per day, with protection from intense mid-day sun

Eucalyptus

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