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Acacia melanoxylon

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Acacia melanoxylon is a significant tree species native to south-eastern Australia. It is widely known by many names, including Australian blackwood, hickory, and Tasmanian blackwood. This tree belongs to the Plurinerves section of the Acacia genus. It is one of the most widespread tree species in eastern Australia. Because it grows in so many different environments, the tree can vary quite a bit. These variations often appear in the size and shape of its parts.

BlackwoodAcaciaPhyllode2
BlackwoodAcaciaPhyllode2

The structure of the tree is very distinct. It features a bole, or main trunk, that reaches a specific diameter. The bark on older trees is dark grey to black. This bark is deeply fissured and often looks scaly. The branches are angular and have ribs. On younger plants, the stems may occasionally be hairy. However, younger branches are usually glabrous, which means they are smooth and hairless. These branches are ribbed and can appear angular or flattened near the greenish tips.

A fascinating feature of this tree is that it has phyllodes instead of true leaves. A phyllode is a modified leaf stalk that functions like a leaf. These phyllodes are glossy, leathery, and dark green or greyish-green. They are usually between 50 and 150 millimeters long and 5 to 25 millimeters wide. Most phyllodes have a narrowly elliptic or lanceolate shape. They are often straight or slightly curved and taper near the base. You can also identify them by their three to five prominent longitudinal veins.

BlackwoodAcaciaPhyllode2
BlackwoodAcaciaPhyllode2

The life cycle of the tree includes a specific blooming period. Between July and December, the tree produces inflorescences. These are groups of flowers that grow on an axillary raceme. The flowers form spherical heads with a diameter of about 10 to 15 millimeters. Each head contains 30 to 50 densely packed flowers that are pale yellow or nearly white. After the flowers fade, the tree develops seed pods. These pods are smooth, papery, and glabrous. They are often curved, twisted, or coiled in a biconvex shape. These pods contain seeds arranged longitudinally.

Scientists have a long history of classifying this species. The botanist Robert Brown first formally described the tree in 1813. He included his findings in a work called Hortus Kewensis. In 1986, Leslie Pedley reclassified the tree as Racosperma melanoxylon. However, the scientific community returned it to the genus Acacia in 2006. This tree is found across a massive range in Australia. It stretches from Queensland in the north down to South Australia. It is also common along the east coast of Tasmania. In New South Wales, it grows from coastal areas into the Great Dividing Range.

The timber of Acacia melanoxylon is highly valued for its beauty and strength. The heartwood is golden to dark brown with chocolate growth rings. The sapwood is lighter, ranging from straw to grey-white. The wood is straight-grained, though it can sometimes be wavy or interlocked. It has a density of approximately 660 kg/m3. This makes it strong in compression and resistant to impact. It is also moderately stiff and bends well. Woodworkers often notice that the wood is lustrous with a fine to medium texture. It even has high chatoyance, which is a visual effect where the wood seems to shimmer.

BlackwoodAcaciaPhyllode2
BlackwoodAcaciaPhyllode2

Humans have used this tree for many different purposes throughout history. Indigenous Australians have used many parts of the plant for survival. They harvest the seeds as a common bush tucker food. The leaves can be used as a soap or as a fishing poison. The bark can be used to make string or prepared as an analgesic to relieve pain. The wood is used to make traditional items like clap sticks, spear-throwers, and shields. Today, the timber is used commercially for fine cabinetry and musical instruments. It is a popular choice for making guitars, drums, and violin bows. Because it can be shaped with steam, it is also used in boatbuilding.

While the tree is useful, it can also cause problems in new environments. Acacia melanoxylon has been introduced to many places like Africa, Asia, Europe, and the United States. In some areas, it is considered an invasive species. For example, it is a declared noxious weed in South Africa and a pest in the Azores Islands. In some parts of Tasmania, it is even considered a pest. In some cities, officials are phasing out its use as a street tree. This is because the roots can cause damage to pavements and underground plumbing.

BlackwoodAcaciaPhyllode2
BlackwoodAcaciaPhyllode2
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