Casuarina equisetifolia ssp. incana

coastal casuarina


Casuarina equisetifolia ssp. incana

(Benth.) L.A.S.Johnson 1982

pronounced: kaz-yoo-ah-REE-nuh eck-wee-set-ih-FOH-lee-up subspecies in-KAH-nuh

(Casuarinaceae — the she-oak family)


common names: casuarina, coastal she-oak, horse-tail she-oak

native 4Both the family and genus names are from the Malay word kasuäri, the cassowary, so named because of the tree’s similarity to that bird’s plumage. The word equisetifolia comes from three Latin words, æquus, equal, sæta, a bristle, and folium, a leaf. Incana (from incanus) is Latin for grey or hoary.

The she-oak is native to Australasia, south-east Asia, and islands of the western Pacific. It also grows well in the coastal areas of India and the Caribbean. It is a fast-growing evergreen up to 10 metres high.

To my mind, the line of casuarinas on our beaches is one of the most attractive features of the island. There is something magical in looking out to sea with the drooping foliage of these trees framing the scene. The best stand of casuarinas is at Florence Bay, especially at the northern end, where they stretch back quite a distance from the shoreline. Unfortunately the trees of this species have only a relatively short life, and are very susceptible to cyclones. The Picnic Bay foreshore trees had virtually disappeared, apart from a few saplings, when a replanting operation was undertaken a few years ago. The seedlings planted were all descended from the original Picnic Bay trees, and flourished. Alas, many of the new plantings were destroyed in cyclone Yasi. Similar replantings have also taken place at Florence Bay. The roots of the trees play an important part in stabilizing the sand just above the high tide line.

Our species is monoecious, although most species in the family are dioecious. The flowers are produced in small catkin-like inflorescences, the male flowers in simple spikes, and the female on short pedicels. The female flowers have no sepals or petals, and consist of a single pistil with a scarlet end receptive to pollen. The male flowers at certain times of the year produce large quantities of wind-blown pollen. When this occurs, parts of the trees change to a rusty red colour. The branches carrying the male flowers eventually drop off. The she-oaks do not produce nectar, but bees do collect the pollen.

The trees are notable for their long, segmented branchlets (cladodes) that function as leaves. They look a bit like pine needles, although the she-oaks are actually flowering plants. The leaves arereduced to tiny scales (leaf-teeth) that encircle eachjoint, thus reducing the surface they would otherwisepresent to the sun’s drying rays. Fallen branchlets of this salt-tolerant tree form a dense, soft mat on the ground beneath, hindering the development of undergrowth.

The fruit is a spiky, woody, oval structure superficially resembling a conifer cone, but is actually a woody fruit made up of numerous carpels each containing a single seed with a small wing.

A surprisingly large number of caterpillars use this tree as a food plant, including:
       • Aenetus splendens,
       • the yellow-spotted Epicoma Epicoma contristis,
       • the Grey Anthelid Munychryia senicula,
       • Porela galactodes,
       • Catoryctis subparallela,
       • the Ash-grey Geometrid Corula geometroides,
       • the Cluster Caterpillar Spodoptera litura, and
       • the She-Oak Moth Pernattia pusilla.

The wood of this tree is used for shingles and fencing, and makes excellent, hot-burning firewood.

As with legumes, she-oak roots possess nitrogen-fixing nodules; this fact, together with their highly drought-adapted foliage, enable them to thrive in very poor soils and semi-arid areas, though they are much less bushfire-tolerant than eucalypts.


Photographs taken in Picnic Bay 2005-2010
Page last updated 3rd November 2018