Acacias: Part 1: An Introduction to Acacias
(Editor's Note: This article was originally published on March 6, 2008. Your comments are welcome, but please be aware that authors of previously published articles may not be able to promptly respond to new questions or comments.)
Acacias are a major feature of the Australian flora, but they are not restricted to Australia. There are over 1500 species in the genus Acacia, world-wide, of which about 950 are Australian, over 130 in Africa, 100 in Madagascar, 270 in the Americas and 55 in the Asia/Pacific region.1
The Acacias have such an important place in the Australian flora that one species, the Golden Wattle - Acacia pycnantha (pictured on the right) was chosen as the floral emblem of Australia and has featured on some Australian stamps.
| Acacia dealbata|
Acacias are mostly spectacular in flower and are often covered with flowers providing dense patches of some shade of yellow to cream, with a few exceptions. Flowers can be so dense as to almost conceal the foliage as in this Silver Wattle - Acacia dealbata in my garden.
| Acacia mearnsii|
Acacias are legumes, closely related to the many pea flowers and shrubs and also to the cassias. The flowers of the Acacias and its closest allies are very different from peas and cassias, in that the petals are greatly reduced and the flower is dominated by the conspicuous stamens. The flowers are compacted into usually dense heads (often globular) and the petals are almost completely concealed except in the bud stage. This close-up of the flowers of the Black Wattle – Acacia mearnsii show both buds and flowers. Black Wattle flower heads contain 20 to 40 flowers per dense flower-head, so that the short stem in the picture will contain nearly 200 flowers.
| Acacia dealbata|
But although the individual flowers are tiny, the seed pods are quite large, up to 15 cm long for the Black Wattle and a tree can be weighed down by the weight of the pods, even if only 1 flower in each head is fertilised. Here is a picture of seed pods on a Silver Wattle. Each pod may hold up to about 12 seeds and the seeds have a hard dark coating. This coating prevents the seed from drying out and it is so effective that seeds can
| Acacia dealbata|
I have seen this longevity of the seeds for myself. Recently we wanted to grow some Blackwood – Acacia melanoxylon for a revegetation project and it had been a very poor year for Blackwood seed. A local farmer produced a packet of Blackwood seed that he had collected in the 1950’s. We treated some with boiling water as usual and most of the 50 year old seeds germinated.
You may have noticed that several of the Acacias referred to are called Wattles. In Australia, all Acacias are collectively known as wattles. This comes from the practice of early settlers in Australia of building houses using the ‘wattle and daub’ technique. The word 'wattle' is of Anglo-Saxon origin and refers to flexible lengths of branches woven between stakes for t
| Female Ganggang Cockatoo|
Apparently the branches of Acacias were found the most suitable for this construction and the name wattle has been used for the Acacias ever since.
Despite the hard outer coating, there are still birds in Australia that feed on Acacia seeds.
The Gang-Gang Cockatoo visits our garden each year to feed on the Cootamundra Wattle – Acacia baileyana seeds and they also feed frequently on the seeds of the Black Wattle as seen here. But despite their powerful beak, they seem to choose to feed on the seed before they are fully ripe and before the hard outer casing has formed.
| Common Bronzewing|
The Common Bronzewing Pigeon also feeds on Black Wattle seeds, but it feeds on the ground, so the seed it finds are all ripe hard seed shed by the trees.
| Acacia victoriae|
Many species were important plants for the aboriginal people of Australia:
| Acacia dealbata Acacia mearnsii |
Silver Wattle, MART Black Wattle, KORONG = gum
Silver Wattle is common in mountain forests. Black wattle is widespread at low elevations. Both species were used in the same ways. The seeds were either ground to make flour for damper or steamed and eaten whole. The seedpod was split with a stone knife, the seeds beaten out, winnowed on bark and ground with grinding stones. Gum was eaten, sometimes mixed with mannas, or made into a sweet drink and left to ferment. The bark was used as a medicine, by making a decoction, used to slow major bodily processes and used as a remedy and treatment for diarrhoea, haemorrhage, heavy menstrual flow, as well as many other uses. The wood was used to make handles for implements and the inner bark was made into string.2
Blackwood was a favourite timber for the Ganai for boomerangs, shields and coolamons. The roots and bent branches were favoured for boomerangs. Bark was used to make fishing lines and for making a decoction for treating rheumatism. Bark and twigs were used as a poison for fish.2
The timber of Blackwood has become an important timber in modern Australia as it is very decorative and is often used in making quality furniture. The background of this marquetry document box, which I made, is an example of the use of Blackwood timber.
1. Flora of Australia Volume 11A, Mimosaceae, Acacia part 1, Melbourne: ABRS/CSIRO Publishing (2001).
2. De Souza-Daw, R., Harris, K. and Paton, D. Plants of Significance to the Ganai Community. Woollum Bellum KODE School (2000)