Acacia decurrens
SYDNEY GREEN WATTLE
Acacia irrorata
CINNAMON GREENWATTLE
Family: MIMOSACEAE
I have walked past these plants in Duggan and Hancock Parks (Toowoomba) many times, and simply failed to notice that they are not the ordinary local greenwattle, Acacia irrorata, which is a very similar plant.
I wasn’t certain whether to be disappointed or delighted. Really, they are an environmental weed. However they are also a part of Toowoomba’s history - a reminder of a lost industry.
Native to the area around Sydney, their value as a source of tanbark was recognised early in our colonial history, and bark-strippers began plundering the naturally-growing plants. To ensure an ongoing supply, Sydney greenwattle plantations were established up and down Eastern Australia, to produce bark for tanning leather. They were also introduced to southern Africa and California. They have naturalised, and are spreading in many of these habitats, where they are now an environmental weed. Around Toowoomba, however, they are not aggressive colonisers, so are not an weed of any serious importance.
Whether they produced better bark for tanning than our local green wattles is doubtful. As we so often see, a certain plant becomes popular,often because it is simply better known, because its natural habitat is near a major cit. Then it planted in other areas regardless of whether there is a better local plant available. The people establishing the Toowoomba plantations would have found the seed of the Sydney greenwattle easy to obtain, and might not have even investigated the qualities of the bark of the local species, let alone wanted to pay staff to collect its seed. Here, they would have been used in our once-thriving and prosperous tanneries.
Our local Acacia irrorata is a plant with a wider natural range extending from Gympie to Gippsland. Down south, they call it “blueskin”. I have no idea why. Perhaps a southern reader will enlighten me? It is also called Cinnamon Greenwattle, because of the cinnamon scent of its leaves - a scent which is absent in A. decurrens.
As new seedlings, both species look remarkable similar. However, distinguishing the two is quite easy, even from a distance, once they have reached a metre or more tall. Acacia decurrens has a shiny, bright green look about it, while Acacia irrorata has softer-looking, non-shiny, dull green leaves. There is also a slight difference in the colour of the flowers, with A. decurrens having more strongly yellow flowers, while those of A. irrorata are a more creamy yellow.
Acacia decurrens has a noticeable gland on the leaf-stem (petiole). Both of them have glands further along, between the leaflets, but A. irrorata has no gland on the petiole.
The fresh yellow growth tips also differ. Those of A. A. decurrens are usually hairless, while A. irrorata has growth tips that are softly hairy to the touch.
The tiny leaflets of A. irrorata are no longer than 5mm long. In A. decurrens they are always longer then 5mm, and can be as much as 15mm.
Which One to Grow?
Local people choosing to grow a plant species for environmental reasons should choose Acacia irrorata because it occurs naturally in the Toowoomba district. It has always been very common locally. (It is the plant that Greenwattle Street is named for.) It is a fast-growing plant with a life-span of not much more than 15 years, which makes it an excellent choice for beginning the task of restoring a wildlife habitat where the land has been cleared of trees. It is also a great plant for creating a fast windbreak, where several rows of trees are to be planted. One row could be of this species, which will be up and doing the job while the more long-lived species are getting their act together.
It attracts a very wide variety of insects, so brings in birds and other insect-eating wildlife species.
Photo: Acacia irrorata
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