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Through Species, Australia and Inflorescence
Description
A. melanoxylon is able to grow to a height of around 20 m (66 ft) and has a bole that is approximately 150 cm (59 in) in diameter. It has deeply fissured, dark-grey to black coloured bark that appears quite scaly on older trees. It has angular and ribbed branches. The bark on older trunks is dark greyish-black in colour, deeply fissured and somewhat scaly. Younger branches are glabrous, ribbed and angular to flattened near the greenish coloured tips. The stems of younger plants are occasionally hairy. Like most species of Acacia, adult plants have phyllodes rather than true leaves. The glabrous, glossy, leathery, dark green to greyish-green phyllodes have a length of 4 to 16 cm (1.6 to 6.3 in) and a width of 6 to 30 mm (0.24 to 1.18 in) with a variable shape. They most often have a narrowly elliptic to lanceolate shape and are straight to slightly curved and often taper near the base and have three to five prominent longitudinal veins.
In its native habitat it blooms between July and December producing inflorescences that appear in groups of two to eight on an axillary raceme. The spherical flower heads have a diameter of 5 to 10 mm (0.20 to 0.39 in) and contain 30 to 50 densely packed pale yellow to nearly white flowers. Following flowering, smooth, firmly papery and glabrous seed pods form. The curved, twisted or coiled pods have a biconvex shape with a length of 4 to 12 cm (1.6 to 4.7 in) and a width of 5 to 8 mm (0.20 to 0.31 in) and contain longitudinally arranged seeds.
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Taxonomy
The species was first formally described by the botanist Robert Brown in 1813 as a part of the William Aiton work Hortus Kewensis. It was reclassified as Racosperma melanoxylon by Leslie Pedley in 1986 then returned to genus Acacia in 2006. Several other synonyms are known including Acacia arcuata, Mimosa melanoxylon and Acacia melanoxylon var. obtusifolia.
Distribution
In its native range, A. melanoxylon is found down the east coast of Australia from Queensland in the north, into New South Wales, through Victoria and west along the south coast of South Australia. It is also found along the east coast of Tasmania. It has become naturalised in Western Australia. In New South Wales it is widespread from coastal areas and into the Great Dividing Range but is not found further inland. It is commonly found at higher altitudes in the Nandewar Range, Liverpool Range and around Orange in the west. It is mostly found as a part of wet sclerophyll forest communities or near cooler rainforest communities. The range of the tree extends from the Atherton Tableland in northern Queensland and follows the coast to around the Mount Lofty Range in South Australia and can grow in a wide range of podsols, especially in sandy loams.
Timber
A. melanoxylon is valued for its decorative timber which may be used in cabinets, musical instruments and in boatbuilding.
Appearance
Sapwood may range in colour from straw to grey-white with clear demarcation from the heartwood. The heartwood is golden to dark brown with chocolate growth rings. The timber is generally straight grained but may be wavy or interlocked. Quartersawn surfaces may produce an attractive fiddleback figure. The wood is lustrous and possesses a fine to medium texture.
The name of the wood may refer to dark stains on the hands of woodworkers, caused by the high levels of tannin in the timber.
Properties
A. melanoxylon timber - commonly known as "blackwood" - has a density of approximately 660 kg/m3 and is strong in compression, resistant to impact and is moderately stiff. It is moderately blunting to work with tools and bends well. It may be nailed or screwed with ease, but gluing may produce variable results. The wood is easily stained and produces a high-quality finish.
Australian blackwood seasons easily with some possible cupping when boards are inadequately restrained. The timber produces little movement once seasoned.
The timber is susceptible to attacks by furniture beetles, termites and powder-post beetles (sapwood) due to its physical resistance to effective preservative treatments.
The timber provides very high chatoyance, with an average value above 26 PZC.
Invasive species
The species has been introduced to many countries for forestry plantings and as an ornamental tree. It now is present in Africa, Asia, Europe, Indian Ocean, the Pacific Ocean, South America and the United States. It is a declared noxious weed species in South Africa and is a pest in Portugal's Azores Islands. It was also recently listed by the California Invasive Plant Council (Cal-IPC) as an invasive weed that may cause limited impact (Knapp 2003). Its use as a street tree is being phased out in some locales because of the damage it often causes to pavements and underground plumbing. In some regions of Tasmania, blackwood is now considered a pest.
Uses
Indigenous Australians use many parts of A. melanoxylon for a variety of purposes. Seeds are harvested and consumed as a common bush tucker food, and leaves can be used as a soap or fishing poison. The bark is either harvested to make string or prepared as a traditional analgesic, while wood is often used to make clap sticks, spear-throwers and shields.
The live plant is also employed as a fire barrier in rural settings when grown amongst other fire-resistant species.
Blackwood timber is commercially milled for wood paneling, furniture, joinery and cabinetry, tool handles, boat-building, inlaid boxes and wooden kegs. It is often qualitatively compared to walnut hardwood, and its physical properties are well-suited for shaping with steam. The bark contains a tannin content of about 20%, and is often engineered to produce decorative wood veneer. Plain and figured Australian blackwood is used for musical instruments; in particular, guitars, drums, Hawaiian ukuleles, violin bows and organ pipes. More recently, blackwood has seen an increasing value as a substitute for koa wood.