Casuarina cones

Casuarinas are quintessentially Australian to most Australians. Perhaps not to the same degree as eucalypts and acacias, but they are certainly a key component of the Australian flora and psyche. From the whispering river-oaks of inland water courses, to the beach-delimiting she-oaks of various kinds, to the inland bull-oaks or bulokes of the Murray-Darling.

River oaks, Casuarina cunninhamiana, along the Abercrombie River in central New South Wales.

Coastal she-oak, or beach casuarina, Casuarina equisetifolia ssp incana growing on beach sand on Lady Musgrave Island in the Great Barrier Reef (see Heron & Lady Musgrave Islands post).

Casuarinas belong to the Family Casuarinaceae. For a long time this family was considered to be fairly primitive within the dicotyledonous plants, and was placed pretty much out on its own, often being put in its own Order (major grouping of plants). But more recent work indicates it actually fits within the Order Fagales, which includes birches, aspens and hazels (Betulaceae), oaks and beeches (Fagaceae), the Gondwanan southern beeches (Nothofagaceae), walnuts, pecans and hickory (Juglandaceae) and a couple of other small related families). Casuarinaceae is thought to be most closely related to Betulaceae.

This placement might seem odd to the casual observer, (I was certainly rather surprised when I looked into it) but they are characterised by having separate male and female flowers, the male flowers often being in the form of catkins, and are wind-pollinated.

The silver birch, Betula pendula, doesn't bear any immediate resemblance to casuarinas!

The Casuarinaceae are distributed essentially throughout Malesia, Australia, and into the south-west Pacific, with a few outliers further afield. And there are a lot of introduced plantings around the globe, particularly in coastal situations. There are considered to be just under 100 species, with 65 occurring in Australia. Originally, all species were within the genus Casuarina, but they have recently been split amongst four genera, the majority in Allocasuarina (61 species) and Casuarina (17 species). But I doubt any one is likely to start using anything but casuarina as the common name for most members of the group (the other two genera are Gymnostoma and Ceuthostoma).

Apart from the immediately distinctive needle-like foliage (which isn’t actually foliage but photosynthetic branchlets – the leaves are reduced to whorls of tiny scale-like teeth), the fruits are also characteristic, being cone-like, and generally referred to as cones, although technically they are woody infructescences. While superficially all rather similar in form, the details of the cones do vary a fair bit. And so finally we get to what this post is about – basically just a gallery of photos of the cones of some of the local casuarina species.

River oak or River she-oak  Casuarina cunninghamiana
This is one of the most common of the casuarinas around Canberra and apart from occurring naturally along the local river courses, it is also planted extensively as a landscape tree.

Young developing cones with dried off styles of the withered 'flowers' still adhering

The flowers/cones frequently develop as terminal or sub-terminal clusters

Early stage cone of Casuarina cunninghamiana

Immature cones along a branchlet

A tight cluster of mature cones, but mostly not yet opened to release their seeds

Drooping She-oak  Allocasuarina verticillata (prev. C. stricta)
This is another species that occurs commonly in Canberra, but is generally more restricted to grassy woodlands and rocky hillsides. In contrast to the cones of C. cunninghamiana which are really quite small, the cones of A. verticillata are large and chunky.

Developing cone of the drooping she-oak Allocasuarina verticillata

The stalk or peduncle is often quite short, the cone sometimes appearing to grow straight out of the branch

Mature, partly opened cones of drooping she-oak

Old cones often persist on the tree for years - this one supporting lichen growth

Black she-oak  Allocasuarina littoralis
Although the specific name littoralis indicates a coastal distribution, the black she-oak also grows well inland. Nevertheless, the following photos were taken at Narooma on the New South Wales south coast.

Young developing cone of the black she-oak

Cluster of three developing black she-oak cones in early morning sunlight

Mature cones of black she-oak showing characteristic shape

Allocasuarina distyla
For some reason, this species doesn't have an accepted common name, despite it having by far the most attractive cones of the four species included in this post. It occurs in Sydney sandstone areas, particularly in heathland associations. These photos were taken at Currarong near Jervis Bay.

Allocasuarina distyla - flower head developing into a cone

Cluster of three young developing Allocasuarina distyla cones

Developing Allocasuarina distyla cone

Rich colours of a develoiping Allocasuarina distyla cone.
The pointed end (due to sterile apical flowers) is fairly characteristic of this species.

Mature but unopened cone of Allocasuarina distyla

Allocasuarina distyla cone fully opened and seeds released

One final point on leaving – the name casuarina derives from a Malay word, kasuari, which means cassowary, in allusion to the supposed similarity between the tree’s foliage and the bird's plumage. And the equisetifolia part of the scientific name of the coastal she-oak Casuarina equisetifolia, comes from the Latin, equisetum, meaning horse hair, this time in reference to the resemblance of the drooping foliage to a horse's tail. Hmmm!

See earlier post -  Missy - for the story of this semi-tame cassowary

Fascinating fasciation and other casuarina growths

Wow! what a weird, spectacular mutation!

That was my first thought when I noticed an amazing expansion and deformation of the growing tip of a young casuarina at the top of Red Hill in Canberra.

I had just begun the December 2010 quarterly survey of Red Hill as part of the Canberra Ornithologists Group Woodland Bird Survey when I came across it on the side of the track. And luckily I had my camera with me on that occasion. I hadn’t seen anything quite like it before; nor since.

The fasciated growing tip of a casuarina (Allocasuarina verticillata) in Canberra.

A less extreme (or earlier in development?) example of fasciation on the same casuarina.
For a size estimate, the ant (a common Sugar Ant Camponotus consobrinus) is about 15 mm long. 

These exceptional growths are the result of a process called fasciation which, although rare, is common enough that the condition is well known in a wide range of plants. Indeed some plant cultivars have been developed, especially of certain cacti, daisies, and the cockscomb (Celosia argentea), specifically for this ‘feature’ (see for example http://wimastergardener.org/?q=fasciation ).

The word comes from the Latin fascia meaning ‘a band’, and alludes to the typical broad flat ribbon-like structures that commonly result. Although this broad banding is perhaps the most common pattern, fasciation can also manifest as radial or adventitious additional flowers growing out of the main flower, sometimes referred to as ‘hen and chicks’. I wish I’d known this earlier this year when I had several orange daisies in the front garden with this condition – I thought at the time it was just how they grew, but since then they’ve all been quite normal!

In simple terms, fasciation results from the abnormal growth of the meristem tissue (i.e. the growing tip of the plant, be it stems, flowers, roots etc). The underlying reason for this may be physical damage (including frost damage), insect damage, bacterial, viral or fungal infections, hormonal imbalances, or genetic mutation. 

It seems that casuarinas, and particularly the Drooping She-oak Allocasuarina verticillata, may be prone to such fasciation – see for example http://www2b.abc.net.au/science/scribblygum-old/posts/topic9591.shtm , and especially http://medlarcomfits.blogspot.com.au/2007/08/more-views-of-that-casuarina.html for some incredible photos.

In fact, Casuarinas seem to be prone to quite a range of growth abnormalities other than fasciation. Below are some examples of a range of ‘defects’ I’ve noticed in several different casuarina species over the past couple of years. These generally have been small and unobtrusive, and presumably result from some similar perturbation to the growing tip of the plant (or might they be insect-induced galls?). 

Abnormal growth in a casuarina, Harrington NSW, July 2012.

Abnormal shoot growth (or gall?) in a casuarina, Harrington NSW, July 2012.

Abnormal shoot growth (or gall?) in a casuarina, Cessnock NSW, February 2014.

Another well-known growth abnormality in trees is what is known as ‘witches’ brooms’. These show up as a dense cluster of shoots arising from the one spot, often resembling a clump of mistletoe. Again, the causes for these growths may be varied, and may relate to infection by rust and other fungi, viruses, bacteria, mite or insect damage, or even mistletoes.

So to come full circle, on the latest Red Hill woodland survey, done just last Friday morning, I photographed the example below. Clearly, it had been growing in this tree (again an Allocasuarina verticillata) for quite a while – the witches’ broom is a bit over a metre in length – but, despite hanging right over the main access road, this was the first time I had really noticed it. Perhaps because I had this blog post in mind!

A pendulous witches' broom in an Allocasuarina verticillata on Red Hill, Canberra, ACT, September 2014.

The witches' broom is a dense clustering of twisted, shortened, casuarina needles.

So I’ll keep my eye out for further growth abnormalities in casuarinas (and other plants). And while I’m at it, perhaps I should get myself a copy of a recent book by Rosalind Blanche that sounds really interesting called Life in a Gall: the Biology and Ecology of Insects that live in plant galls. Galls really are another story entirely…