Robert Powell: Tree Pictures, South-Western Australia
Common sheoak (Allocasuarina fraseriana)
Like the tree-banksias, common sheoak is a common component of the understoreys of Perth’s eucalypt forests and woodlands. But whereas the banksias are admired for their showy flower-spikes, common sheoak is little appreciated. This is a great pity, since common sheoak has a beautiful form.
Many sheoak species are among the toughest Australian trees, able to withstand unusually harsh conditions. Beach sheoak (Casuarina equisetifolia), for example, grows in very salty coastal environments, and desert oak (Allocasuarina decaisneana) in the deep sands of hot, dry Central Australia. Common sheoak, however, is not one of the tough species. It needs a moderate amount of moisture and does not occur very far north of Perth. Nor does it tolerate salt winds particularly well. Even if only mildly exposed to them it will often show an asymmetrical shape in response to the dying back or stunting of growth on its seaward side. This sculpturing by the salt lends the trees additional character.
The foliage of sheoaks comprises what are commonly known as ‘needles’: slender, flexible green branchlets that function as leaves. The true leaves are very reduced, appearing as tiny ‘scales’ in whorls round the branchlets.