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Eucalyptus
[edit] Leaves
The leaves on a mature eucalypt plant are usually completely different in shape, size, colour and other charateristics from those of a seedling, Four leaf phases are recognised in the development of a eucalypt plant - the ‘seedling’, ‘juvenile’, ‘intermediate’ 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 Eucalyptus 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. The first few to many pairs in most species may be sessile or petiolate. Later pairs which have been formed opposite as usual at the stem apex as in the mature plant, become seperated at their bases by unequal elongation of the stem. In the adult leaf phase the leaves of a pair are always petiolate and apparently alternate.
In Western Australia several species are well known because the whole crown is composed of glaucous, juvenile leaves even when the plant is reproductively mature. These are some of the striking ornamental trees, such as Eucalyptus macrocarpa, Eucalyptus rhodantha and Eucalyptus crucis.
Some species are notable for the great contrast between the juvenile and adult phases. Eucalyptus loxophleba is very easy to identify in the field due to its conspicuous, glaucous seedlings and contrasting shiny, dark green adults. Conversely, Eucalyptus caesia has bright shiny green leaved seedlings and dull, glaucous leaves in mature crowns.
A few species have shiny green leaves throughout their life cycle - including Eucalyptus petraea, Eucalyptus dundasii and Eucalyptus lansdowneana.
While there is great diversity in the form of leaves in the early phases, there is significant similarity in form in the adult phase and in most species the adult leaves are lanceolate, stalked, alternating and green.
There is no definite transitional point between the phases. The intermediate phase, when the largest leaves are often formed links the juvenile and adult ones.
[edit] Leaf Characteristics
petiolate - with a leaf stalksessile - without a leaf stalkorbicular - almost roundovate - broader below the middle, pointed at the end, length:breadth up to 3:1cordate - heart shaped, usually ovate and indented at the basebroad-lanceolate - lance-shaped, finally pointed, length:breadth up to 5:1elliptical - roughly in the form of an ellipse, tapering fairly evenly at both ends, which can be rounded or pointedlanceolate - lance-shaped, finally pointed, length:breadth up to 8:1narrow-lanceolate - elongated, finally pointed, length:breadth more than 8:1linear - very narrow, sides parallel for most of the length of the leaf, length:breadth approx 12 (or more):1falcate - curved like the blade of a sickleoblique - the two halves of the leaf blade meet at different points on the petiolehairy - with hairs on the leaves and stemsundulate - having a wavy surfaceglossy - the leaf surface is shinydull- the leaf surface is not shiny unless viewed very obliquelyconcolorous - the leaf is the same colour on both sidesdiscolorous - the upper and lower leaf surfaces are different in colourglaucous - having a coat of white wax
[edit] Eucalyptus sideroxylon
E.sideroxylon is one of the best known of the Ironbarks. There are two subspecies recognised; subsp. sideroxylon is the common form found over most of the range of the species except that it only has a very slight incursion into Victoria.
Subsp.tricarpa is found along the south coast of New South Wales, the north-east coast of Victoria and in central Victoria. The latter differs from subsp. sideroxylon in having fewer flowers in its inflorescence, larger buds and fruit and broader juvenile foliage.
Flowers are normally well displayed and are usually white. However, pink and red flowering forms are fairly common with both recognised varieties and are popular in cultivation.[1]
Leaf: Alternate (juvenile foliage may be opposite), simple, evergreen, leathery, ovate to narrowly lanceolate, 4-8 inches long, often curved and drooping, long pointed, entire margins, aromatic, dull green above, bluish bloom beneath, young foliage more blue.
Flower: Round, 2 inches across, with very long red to pink (sometimes white) stamens, no petals, making it look like a round bottle brush, clustered in leaf axils in winter and early spring.
Fruit: An urn-shaped capsule 3/8 inch long, in clusters.
Twig: Slender and red with a white bloom, smooth.
Bark: Deeply ridged and furrowed, hard, dark red to black, does not shed.
Form: A medium to large tree to 100 feet, usually slender and may have drooping branches. Cite error: Invalid <ref> tag; refs with no name must have content
Red Ironbark is a highly valuable tree because of its adaptation to many sites, strong wood and ability to grow well in smog. This tree has been cultivated as well outside of Australia, in countries that include the US, Brazil and many Mediterranean areas. It originates in Queensland, grows through NSW and into the north-eastern areas of Victoria. The only indigenous Ironbark in Melbourne is the closely-related E. tricarpa.
‘Rosea’ Red Ironbark is a seed selection that is red flowering. In all other attributes, it is identical to the species, but typically will grow slightly smaller—to 20m, rather than the possibility of a 30m tall tree. The growth is normally upright on juvenile trees, but trees begin spreading with age and can become 15m wide. The bark of this tree gives it its common name; Red Ironbarks have deeply fissured plate-like bark that is a rusty red beneath and black on the surface. This bark contrasts well with the foliage, which is dark green to grey-blue.
‘Rosea’ Red Ironbark will grow successfully on many sites, including those alkaline areas. For best growth, a well-drained site in full sun should be selected. Establishment is rapid with good quality planting stock, and Red Ironbark should be fully established after 2 years. Trees will grow up to 1200mm per year given ideal conditions.
Bifurcation, or co-dominant leaders, can be problematic with Ironbarks. It is essential that this tree be purchased as a single-leader specimen with good formative canopy development.
Patterns of Variation in Eucalyptus sideroxylon A. Cunn. Ex. Woolls. I. Variation in Adult Morphology
HW Bramwells and T Whiffin
Abstract
Eucalyptus sideroxylon, a woodland tree occumng in an arc from central and southern Victoria to south-eastem Queensland, is currently divided into subsp. slderoxylon to the north, and subsp. tricarpa to the south. Thirty populations were sampled throughout the range of the species and studied for adult leaf and fruit characters. There were found to be very marked and highly significant morphological differences between the two subspecies, more especially in the fruit characters. Within subsp. sideroxylon there was a general distinction between the inland populations and the more coastal populations, while within subsp. trlcarpa there was similarly a general differentiation of the coastal populations from the northern and north-central Victorian populations. The extent and general pattern of these various differences are documented as a prelude to further studies. [1]
[edit] Corymbia
Following work published in 1995 by the Australian botanists K.D. Hill and L.A.J. Johnson ( Telopea 6(2-3):185-504), the Australian Tree Seed Centre now recognises the bloodwood and ghost gum groups of eucalypts as a distinct genus. The new scientific name for this genus is Corymbia. Thus some commonly known bloodwoods such as Eucalyptus maculata (Spotted Gum) and E. citriodora (Lemon Scented Gum) now have a new generic name and will be known as Corymbia maculata and C. citriodora respectively.
[edit] List of Corymbia Species
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