<P> 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 . </P> <P> 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 . </P> <P> 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 . </P> <P> 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 . </P>

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