The lightwood tree (Acacia implexa) is an Australian native evergreen tree commonly used for timber. The tree is also known by some interesting folk names, such as hickory wattle, fish wattle, broad-leaf wattle, sally wattle, and scrub wattle, as well as bastard myall, which is a folk name applied to several Australian trees in the Acacia family. It is a close relative of Acacia mangium and is sometimes confused with it as their woods are similar.
The lightwood tree has a greyish brown bark and evergreen oval, sickle-shaped leaves (which are not true leaves but actually flattened stems known as phyllodes) that sometimes appear purple based on soil condition. The growth cycle brings flowers, leaves and finally seed pods. The showy flowers arrive in summer, cream-colored to pale yellow, formed in a burst of round spiky flower heads that are strongly fragrant. The flowers are followed by a twisted cylindrical seed pod that has an unusual texture and appearance, a bit like a large pea pod, that starts out green and slowly turns reddish brown.
The tree has a long history of being used for many practical purposes by the Aboriginal people of Australia, including for string, rope, medicine, and flour made from the seeds. It's also used to make "fish poison" (a substance traditionally used by the Aboriginal people to make fish easier to catch). The leaves may also be used to make yellow or brown dye. The tree was first formally noticed by visiting English botanists in 1842, but as a well-known native tree it was in significant use well before that.
Although the lightwood tree is familiar and well-loved in Australia for its showy blossoms and easy care, it can be quite invasive in non-native environments. It is vigorous, long-lived and fast-growing, which adds to its undesirability in areas where it has invaded. It is currently considered an invasive alien species in South Africa, where it was originally planted as a planation crop. Now the tree invades farmlands and other open areas and spreads rapidly there, with little to be done other than cutting them down as fast as they pop up.
|Botanical Name||Acacia implexa|
|Common Name||Hickory wattle, fish wattle|
|Mature Size||20-50 ft. tall|
|Sun Exposure||Full sun|
|Soil Type||Sandy, clay|
|Soil pH||Neutral to acidic (5.0 to 7.0)|
|Flower Color||Cream to pale yellow|
|Hardiness Zones||6 to 9, USA|
|Native Areas||Eastern Australia|
|Toxicity||Toxic to livestock|
How to Grow Lightwood Trees
Lightwood trees are mainly found on the eastern coast of Australia, and have become known as an invasive species in non-native regions. Once established as an invasive tree, the lightwood tree can be very hard to control its spread. This is true of various other Australian native plants. For example, tea tree (Melaleuca quinquenervia) was planted throughout south Florida by entrepreneurs thinking it could grow quickly and provide easy profits from its important essential oil used in health and beauty products. But it soon spread so quickly and voraciously throughout the Everglades (a delicate ecosystem) that young trees had to be burned to eradicate them.
The lightwood tree should not be introduced to a North American environment. One reason trees from other parts of the world prove to be invasive in North America is that they're no longer affected by their natural predators (insects, wildlife) who might keep their growth in check in various ways. The only known way to control the spread of lightwood trees is by uprooting them, a method that may not be practical in many areas, especially given the tree's ability to spread suckers on hard-to-access terrain like steep banks.
Lightwood grows in a variety of soil conditions, and is very tolerant of poor soil that is full of sand or clay. This soil tolerance makes it very hardy and useful for bank and erosion stabilization, and it forms suckers readily when the roots are injured.
This tree loves bright sun and grows easily wherever there is ample light for it to proliferate. But even in a sunny spot, first you'll want to consider whether you have room for this tree: its mature height is between 20 and 50 feet tall.
Adequate water is important for the lightwood tree, but it doesn't do well if it is overwatered. Regular watering during times of drought is particularly important to prevent the formation of toxic compounds in the seedpods when the plant is dehydrated; these compounds may poison livestock who might consume the seedpods while they graze on its leaves.
Temperature and Humidity
The lightwood tree is tolerant of both heat and drought, and also fairly frost tolerant for an Australian native tree. It's also quite tolerant of air pollution such as car exhaust so it makes a good choice for planting along roadsides or near parking lots, and also makes a good urban or street tree because of its easy adaptation to many conditions.
Is the Lightwood Tree Toxic?
The seedpods of the lightwood tree can be toxic to livestock. In times of drought, the leaves of different acacia trees, including Acacia implexa, may form an overabundance of Hydrogen cyanide which is toxic to herbivores who eat the foliage including the seedpods. Watering the trees during drought may help lessen this risk and care should be taken to prevent their drying out in areas where livestock have access to them. To be on the safe side, removing acacia trees from livestock grazing areas is the best bet.