Editing Eucalyptus (section)

==Description==
===Size and habit===
Eucalypts vary in size and [[Habit (biology)|habit]] from shrubs to tall trees. Trees usually have a single main stem or [[Trunk (botany)|trunk]] but many eucalypts are mallees that are multistemmed from ground level and rarely taller than {{convert|10|m|ft|0|abbr=off}}. There is no clear distinction between a mallee and a shrub but in eucalypts, a shrub is a mature plant less than {{convert|1|m|ftin|0|abbr=on}} tall and growing in an extreme environment. ''[[Eucalyptus vernicosa]]'' in the [[Tasmania]]n highlands, ''[[Eucalyptus yalatensis|E. yalatensis]]'' on the [[Nullarbor Plain|Nullarbor]] and ''[[Eucalyptus surgens|E. surgens]]'' growing on coastal cliffs in [[Western Australia]] are examples of eucalypt shrubs.<ref name="CANBR">{{cite web |title=Learn about eucalypts |url=http://keyserver.lucidcentral.org:8080/euclid/data/02050e02-0108-490e-8900-0e0601070d00/media/Html/learn.htm |publisher=Euclid: Centre for Australian National Biodiversity Research |access-date=14 March 2019}}</ref>

The terms "[[Mallet (habit)|mallet]]" and "[[marlock]]" are only applied to [[Western Australia]]n eucalypts. A mallet is a tree with a single thin trunk with a steeply branching habit but lacks both a [[lignotuber]] and [[Epicormic shoot|epicormic buds]]. ''[[Eucalyptus 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. ''[[Eucalyptus platypus]]'' is an example of a marlock.<ref name="CANBR" /><ref name="Boland">{{cite book |last1=Boland |first1=Douglas J. |last2=Brooker |first2=M. Ian |last3=McDonald |first3=Maurice W. |last4=Chippendale |first4=George M. |title=Forest Trees of Australia |url=https://archive.org/details/foresttreesaustr00bola |url-access=limited |date=2006 |isbn=0643069690 |page=[https://archive.org/details/foresttreesaustr00bola/page/n363 331]|publisher=Csiro }}</ref><ref name="ANBG">{{cite web |title=Habit |url=http://www.anbg.gov.au/cpbr/cd-keys/Euclid/sample/html/habit.htm |publisher=Euclid: Australian National Botanic Gardens |access-date=29 May 2019 |archive-date=11 March 2007 |archive-url=https://web.archive.org/web/20070311014631/http://www.anbg.gov.au/cpbr/cd-keys/Euclid/sample/html/habit.htm |url-status=dead }}</ref>

''Eucalyptus'' trees, including mallets and marlocks, are single-stemmed and include ''[[Eucalyptus regnans]]'', the tallest known flowering plant on Earth.<ref name=tallest-tree>{{Cite web|url=https://www.bbc.com/earth/story/20141222-the-worlds-new-tallest-tree|title=Tasmania's giant ash trees may be world's tallest|first=Jane|last=Palmer|website=www.bbc.com|access-date=Sep 11, 2020}}</ref> The tallest reliably measured tree in Europe, ''Karri Knight'', can be found in [[Coimbra]], Portugal in Vale de Canas. It is a ''[[Eucalyptus diversicolor]]'' of 72.9 meters height and of 5.71 meters girth.<ref>Karri 'Karri Knight' in the Valle de Canas, Valle de Canas, Centro, Portugal, MonumentalTrees.com https://www.monumentaltrees.com/en/prt/centro/coimbra/4104_valledecanas/8314/ {{Webarchive|url=https://web.archive.org/web/20191227101558/https://www.monumentaltrees.com/en/prt/centro/coimbra/4104_valledecanas/8314/|date=27 December 2019}}</ref>

Tree sizes follow the convention of:
* Small: to {{convert|10|m|ft|abbr=on}} in height
* Medium-sized: {{convert|10|-|30|m|ft|abbr=on}}
* Tall: {{convert|30|-|60|m|ft|abbr=on}}
* Very tall: over {{convert|60|m|ft|abbr=on}}<ref>{{Cite web|url=https://homeguides.sfgate.com/eucalyptus-tree-information-38193.html|title=Eucalyptus Tree Information|website=Home Guides &#124; SF Gate|date=14 August 2012 |access-date=Sep 11, 2020}}</ref>
<gallery class="center">
Tasmania logging 08 Mighty tree.jpg|''[[Eucalyptus regnans]]'', a forest tree, showing crown dimension, [[Tasmania]]
TocumwalTownBeach.jpg|''[[Eucalyptus camaldulensis|E. camaldulensis]]'', immature woodland trees, showing collective crown habit, [[Murray River]], [[Tocumwal]], [[New South Wales]]
Eucalyptus cretata.jpg|''[[Eucalyptus cretata|E. cretata]]'', juvenile, showing low branching 'mallee' form, [[Melbourne]], [[Victoria, Australia|Victoria]]
Eucalyptus angustissima1.jpg|''[[Eucalyptus angustissima|E. angustissima]]'', showing shrub form, Melbourne
Eucalyptus platypus.jpg|''[[Eucalyptus platypus|E. platypus]]'', showing 'marlock' form, Melbourne
</gallery>

===Bark===
All eucalypts add a layer of [[Bark (botany)|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 ''[[Eucalyptus sheathiana|E. sheathiana]]'', ''[[Eucalyptus diversicolor|E. diversicolor]]'', ''[[Eucalyptus cosmophylla|E. cosmophylla]]'' and ''[[Eucalyptus cladocalyx|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 ''[[Eucalyptus macrorhyncha|E. macrorhyncha]]'' or peppermints such as ''[[Eucalyptus radiata|E. radiata]]'') or more tightly adherent (as in the "boxes" such as ''[[Eucalyptus leptophleba|E. leptophleba]]''). In some species (the "ironbarks" such as ''[[Eucalyptus crebra|E. crebra]]'' and ''[[Eucalyptus jensenii|E. jensenii]]'') the rough bark is infused with gum resin.<ref name="CANBR" />

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|E. brachycalyx]]'', ''[[Eucalyptus ochrophloia|E. ochrophloia]]'', and ''[[Eucalyptus occidentalis|E. occidentalis]]''—or only in a thick, black accumulation at the base, as in ''[[Eucalyptus clelandii|E. clelandii]]''. In some species in this category, for example ''[[Eucalyptus youngiana|E. youngiana]]'' and ''[[Eucalyptus viminalis|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 ''[[Eucalyptus deglupta|E. deglupta]]''.<ref name=FieldGuide/>

''[[Eucalyptus globulus|E. globulus]]'' bark cells are able to photosynthesize in the absence of foliage, conferring an "increased capacity to re-fix internal CO<sub>2</sub> following partial defoliation".<ref>{{Cite journal|last=Eyles|display-authors=etal|first=A|date=2009|title=Role of corticular photosynthesis following defoliation in Eucalyptus globulus|journal=Plant, Cell & Environment|volume=32|issue=8|pages=1004–14|doi=10.1111/j.1365-3040.2009.01984.x|pmid=19344333|doi-access=free|bibcode=2009PCEnv..32.1004E }}</ref> 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.<ref>{{Cite journal|last=Saveyn|display-authors=etal|first=A.|date=Summer 2010|title=Woody tissue photosynthesis and its contribution to trunk growth and bud development in young plants|url=http://onlinelibrary.wiley.com/store/10.1111/j.1365-3040.2010.02197.x/asset/j.1365-3040.2010.02197.x.pdf;jsessionid=2DF8853EB94016F034D5922B3E11AB6A.f01t04?v=1&t=j335k1pl&s=2bcf5c5de958a434bce7596540f55ee86e269f4e|journal=Plant, Cell & Environment|volume=33|issue=11|pages=1949–58|via=Wiley|doi=10.1111/j.1365-3040.2010.02197.x|pmid=20561249|doi-access=free|bibcode=2010PCEnv..33.1949S }}</ref>

Different commonly recognised types of bark include:{{cn|date=June 2024}}
* [[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 (gum)|kino]] (a [[sap (plant)|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 [[cork (material)|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.

<gallery class="center">
Apple box bark.jpg|Bark detail of ''[[Eucalyptus angophoroides|E. angophoroides]]'', the apple-topped box
Eucalyptus deglupta-trees.jpg|Coloured bark of ''[[Eucalyptus deglupta|E. deglupta]]'' native to Southeast Asia
Eucalyptus bark.jpg|'Box' bark of ''[[Eucalyptus quadrangulata|E. quadrangulata]]'', the white-topped box
Eucalyptus sideroxylon - bark.jpg|Dark, fissured '[[ironbark]]' of ''[[Eucalyptus sideroxylon|E. sideroxylon]]''
</gallery>

===Leaves===
[[File:Eucalyptus leucoxylon1.jpg|upright|thumb|''[[Eucalyptus leucoxylon]]'' var. 'Rosea' showing flowers and buds with [[Operculum (botany)|operculum]] present]]
[[File:Eucalyptus tetragona - glaucous leaves close.jpg|thumb|''[[Eucalyptus tetragona|E. tetragona]]'', showing glaucous leaves and stems]]

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 [[Myrtaceae|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.{{Citation needed|reason=This section lacks citations|date=March 2019}}

The leaves on a mature ''Eucalyptus'' plant are commonly [[lanceolate]], [[Leaf#Characteristics of the petiole|petiolate]], apparently [[Alternate leaf|alternate]] and waxy or glossy green. In contrast, the leaves of seedlings are often [[Opposite leaf|opposite]], [[Leaf#Characteristics of the petiole|sessile]] and [[Leaf#Surface of the leaf|glaucous]]. But many exceptions to this pattern exist. Many species such as ''[[Eucalyptus melanophloia|E. melanophloia]]'' and ''E. setosa'' retain the juvenile leaf form even when the plant is reproductively mature. Some species, such as ''[[Eucalyptus macrocarpa|E. macrocarpa]]'', ''[[Eucalyptus rhodantha|E. rhodantha]]'', and ''[[Eucalyptus crucis|E. crucis]]'', are sought-after ornamentals due to this lifelong juvenile leaf form. A few species, such as ''[[Eucalyptus petraea|E. petraea]]'', ''[[Eucalyptus dundasii|E. dundasii]]'', and ''[[Eucalyptus lansdowneana|E. lansdowneana]]'', have shiny green leaves throughout their life cycle. ''[[Eucalyptus 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.{{Citation needed|reason=This section lacks citations|date=March 2019}}

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.<ref name=FieldGuide>Brooker & Kleinig (2001)</ref>

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 ''[[Eucalyptus oleosa|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.{{Citation needed|reason=This section lacks citations|date=March 2019}}

===Flowers and fruits===
[[File:Yellow Box blossoms and gumnuts.jpg|right|thumb|''[[Eucalyptus melliodora]]'', showing flowers and opercula]]
[[File:Eucalyptus camaldulensis seeds00.jpg|thumb|Seeds of ''[[Eucalyptus camaldulensis]]'']]

The most readily recognisable characteristics of ''Eucalyptus'' species are the distinctive flowers and fruit (capsules or "gumnuts"). Flowers have numerous fluffy [[stamen]]s which may be white, cream, yellow, pink, or red; in bud, the stamens are enclosed in a cap known as an [[Operculum (botany)|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&nbsp;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.{{Citation needed|reason=This section lacks citations|date=March 2019}}