Sandpaper Wattle, Acacia denticulosa

Among the hundreds of species of Acacia, Acacia denticulosa, Sandpaper Wattle, is one of the most striking. The species was first collected near Mt Churchman by Jesse Young, a member of Ernest Giles’ expedition across the Great Victoria Desert in 1875. Young (1852–1909) was the astronomer and principal plant collector (assisted by William Tietkens). With the consent of Thomas Elder, sponsor of the expedition, he passed his specimens to Ferdinand Mueller, Government Botanist of Victoria (remember, there was no botanist in WA then). The collection totalled about 400 species, of which some 63 were new. Mueller named many of these, including this species, published in 1876. The name refers to the toothed margins of the phyllodes but perhaps the more unusual feature of these is the very rough surface from which the common name is derived. This is due to short, conical outgrowths with gland-like tips that are scattered over the lamina and edges of the phyllodes. The phyllodes and young branchlets (also rough at this stage) are slightly sticky.

In the wild the plant is a shrub up to 4 m tall (bottom left) but in the garden it grows to 6 m and can spread to 8 m wide (bottom left). It has an open, rather ungainly habit. Its bark is almost smooth, pale greyish brown, or brown when wet (bottom right). In full flower the tree appears covered with large, golden, woolly caterpillars (centre left).

I bought my plant as a small seedling in April 2008. It grew quickly and by August 2010 was already 3 metres tall.  Since 2010 it has flowered well, starting in July and continuing to the end of August. One reason for its colourful show is that it usually has several spikes per axil. They have a faint ‘wattle’ scent. The fruit is relatively inconspicuous, being a narrow, undulating pod up to 7.5 cm long and 3–4 mm wide, holding small, dark brown shiny seeds (centre right).

The species has no close relatives. The plant has no lignotuber, hence is killed by fire and regenerates from seed. Given adequate space it does not require pruning.  Should this be necessary it should be done progressively as the plant grows, never cutting below the foliage.

Sandpaper Wattle is rare in the wild, known mainly from granite outcrops from near Mt Churchman south-east to Nungarin, with a record near Wongan Hills. It is a Declared Rare Flora (Threatened). Like another rare species from granite rocks, Eucalyptus caesia, it is proving amenable to cultivation.  A plant in the garden of the previous WA Herbarium grew to a large size.

-Alex George

Sandpaper 1 Sandpaper 2 Sandpaper 3 Sandpaper 4

Photos by Alex show the habit, bark, flowers and young pods.



Brooker, Lesley (2015), Explorers Routes Revisited: Giles 1875 Expedition, Hesperian Press, Carlisle.

Maslin, B.R. & Cowan, R.S. (2001), Acacia denticulosa F.Muell. in A.E.Orchard & A.J.G.Wilson (eds), Flora of Australia 11A: 238, 368, 370, 481, ABRS, Canberra, & CSIRO Publishing, Melbourne.

On Banksias, Dryandras, and Hairy Fish

Classification has always been about putting similar things in the same box. It is how one defines “similar” that changes. The earliest classifications were presumably pragmatic: things you could eat in one box, things you couldn’t eat in another, things you could use for medicines in yet another. In modern classification the idea of evolution determines what is thought to be similar. Hence, one criterion is that all the organisms in the one box should have evolved from a recent common ancestor. No problem there: both Banksias and Dryandras can be assumed to have a recent common ancestor. It is the second criterion that is tricky: all the descendants of a recent common ancestor should be in the same box. Dryandras can be assumed to have evolved from within the Banksias and therefore this criterion requires that they both be in the same genus.

Let us see what happens if we apply these criteria to humans. The mnemonic for remembering the higher classifications is: King Philip Came Over For Good Soup. (Kingdom, Phylum, Class, Order, Family, Genus, Species.) We are in the Kingdom Animalia, Phylum Chordata, Sub-Phylum Vertebrata, and Class Mammalia. Other Classes at the same level are: jawless fish (lampreys and the like); cartilaginous fish (sharks and rays); bony fish; amphibians; reptiles; and birds. Reptiles includes lizards and snakes, crocodiles, turtles and dinosaurs.

The first problem is that birds certainly evolved from dinosaurs. The reptile class therefore does not include all the descendants from the one ancestor; birds must go into the dinosaur box. The next problem is that mammals must have evolved from primitive reptiles, so by the same logic, mammals must also go into reptiles. Those of you who think that Dryandras should be sunk into Banksias must therefore think of themselves as hairy lizards.

But wait, there is more. Where did reptiles evolve from? Surely from bony fish. So reptiles and fish should not be at the same level: reptiles, together with birds and mammals, all must go into the fish class. You are not hairy lizards after all: you are hairy, air-breathing fish.

Or we could decide that it was rather silly and abandon the second criterion.

Jim Barrow