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I've been a Canberran since moving here from Adelaide on the first day of 1980. I now live in suburban Duffy with my partner Louise Maher, ABC 666 radio and on-line journalist. Among my early memories is following Sleepy Lizards (Shinglebacks) around the paddocks north of Adelaide, guarded by the faithful bull terrier. I have always been passionate about the natural world, trying to understand how it works, how the nature of Australia came to be, and sharing those understandings. My especial passions are birds, orchids and mammals. For much of my life I have been a full-time naturalist, running bush tours, writing books etc, doing consultancies, presenting a regular radio slot on local ABC, chairing a government environment advisory committee and running adult education classes. Recently I have eased back somewhat, but am still writing, teaching, doing some radio work and running overseas tours - as part of my fascination with our Gondwanan origins I've been running tours to South America for the past decade. I was awarded the Australian Plants Society Award in 2001 and the Australian Natural History Medallion in 2006, both for services to education and conservation. In January 2018 I was awarded a Medal of the Order of Australia for 'service to conservation and the environment'.

Wednesday, 15 April 2015

Have you seen a Casuarina?

This is the latest in an irregular series on some of my favourite trees, of which there is no shortage. The most recent instalment was here, from where you can follow back if you wish.

Sound doesn't usually feature heavily in talking about plants, but casuarinas are different. The inside of a grove of casuarinas whispers; it's like standing surrounded by aeolian harps. 
Belah Casuarina pauper, Gawler Ranges NP, South Australia.
Belah forms woodlands across dry inland Australia; it used to be known as C. cristata,but the species has been split into two, with cristata found from central Queensland
to central western New South Wales.
The reason for the whispering lies in the foliage, which superficially resembles pine needles; indeed people often mistake them for pines. These 'needles' however are branchlets; look closely and you'll see that each branchlet (or cladode technically, for branches which perform a plant's photosynthetic function) is ringed with tiny teeth. These teeth are the remnants of the leaves, presumably reduced to contain water loss in their often arid environment.
Belah cladodes and leaflets, White Dam Conservation Park, South Australia.
If you enlarge the photo the rings of leaflets are quite obvious.
Australia though is only relatively recently a dry continent, so where did drought-resistant casuarinas come from? I think the answer to that lies in their distribution; while Australia is their stronghold, with some 70 of the roughly 100 species, they are found throughout the western Pacific. Seashores are one of the most ferociously droughted habitats, irrespective of rainfall - plants must effectively compete with soil salt for water. (This is a bit crude, but it'll do for our current requirements.) A plant like a casuarina which evolved on the shore would be pre-adapted to living in the dry inland as the country dried out. 
Belah and Bluebush Maireana sedifolia, White Dam Conservation Park, South Australia.
I think this one is interesting because bluebush is a member of the huge saltbush family Chenopodiaceae,
which I suspect also evolved in coastal environments, where some species are still found.
Some species of course have never left the shores. Horsetail Casuarina (or Sheoak - we'll come back to that name in a while) Casuarina equisitefolia is found on beaches from south-east Asia to north-eastern Australia.
Horsetail Casuarina (and male Great Frigatebird!), Lady Elliot Island, Queensland.
Swamp Oak Casuarina glauca, Cullendulla Nature Reserve, New South Wales.
Here it forms an interface with the mangroves on the right; while the mangroves
are flooded with seawater twice daily, the casuarinas are only inundated at very high tides.
They cope with it perfectly well though.
This one has become a serious invasive weed in the Florida Everglades.

We can get a hint from the previous picture (the Horsetail Casuarina) too as to why the great Linnaeus used the name Casuarina when he based the genus on this species; he thought the foliage resembled the hairy-looking plumage of the Cassowary! Personally I think he worked too many late nights...

In the late 1980s the late and highly respected Lawrie Johnson of the Royal Botanic Gardens, Sydney, split the hitherto single genus Casuarina into four; two of those genera are relatively small and barely represented in Australia (by one very restricted tropical Queensland species) but Allocasuarina, distinguished most obviously by larger and knobbier fruits, now represents more than half of what were previously Casuarina. Not everyone is happy with this change, but most authorities go along with it. I use 'casuarina' in lower case as a group name for the family.

I mentioned that casuarinas are quite pine-like at first glance, but they are legitimate flowering plants. As they are wind-pollinated however the flowers are fairly inconspicuous. Moreover most species have separate male and female plants (that is, they are dioecious); the rest have separate male and female flowers on the one plants (monoecious).
Scrub Sheoak Allocasuaria distyla female flowers and cones, Morton NP, New South Wales.
Black Sheoak A. littoralis male flowers Nowra, New South Wales.
The name sheoak is of vexed origin. It is widely supposed to be an indication that the timber was regarded by early British settlers here as of inferior quality to that of European oak, but I'm not at all convinced. I believe it is one of the many names of indigenous origin which later became anglicised as the origin was forgotten, and a new back-filling origin created. I have several bases for this belief, all of them of course circumstantial (as is the traditional explanation). For one thing the wood was actually valued quite highly. The Sydney Gazette of 1803 reported that "This wood is allowed to rank in Europe with the mahogany of Jamaica." That wood was very highly prized for furniture in particular. There is some beautiful casuarina ('beef wood') furniture in the National Museum. I point too to the occasionally encountered form shiock, and the existence of the name buloke for some inland species (notably C. luehmanii) - surely too much of a coincidence? Moreover the term he-oak is also found, though there is no suggestion the timber of these species is superior. And I find convincing the evidence of Richard Howitt, who in his book Impressions of Australia Felix in 1845 wrote quite explicitly "Shiac is the native name - vulgarised to she-oak". 

I don't doubt that some readers will be quite sure I'm wrong - and they may be right, though I think we can agree that we'll never be entirely certain.

To wrap up, here are some more casuarinas, which I hope you can enjoy as much as I do.
Desert Oak Allocasuarina decaisneana at sunset, Uluru, central Australia.
More on this wonderful species here.
Allocasuarina huegliana Boyagin Rock, Western Australia.
Drooping Sheoak Allocasuarina verticillata, above and below.
Above, Rosedale, New South Wales.
Below, Freycinet NP, Tasmania.
River Oaks Casuarina cunninghamiana, Deua NP, New South Wales.
This species always grows along near-coastal stream lines, forming riverine forests.
Thanks for bearing with me; I hope you can enjoy a casuarina soon.



Kath H said...

Thanks for another interesting post Ian. Lovely species and I like your theory about their origins as coastal trees and rear saltbush may also have evolved similarly. Vy the way, the link in your first para to previous postings on trees does not work.

I have been adding links to some of your your posts to the ANBG Guides Google group. They are good professional development.

Ian Fraser said...

Many thanks for your kind words Kath; I always appreciate it when I hear that someone has found a posting useful or just interesting. I'm particularly delighted to be of use to the ANBG in any way too. I'm a bit puzzled about the link though; it worked for me just now.
Has anyone else had problems?

Flabmeister said...

The link worked correctly - I assume - to the Kurrajong post.

I am fascinated by this genus as they fringe the East Coast of Zanzibar, where they are known as Whistling Pines.

I just wish I had known enough about trees when we were in Tanzania to know which species they were. It was suggested they were an Australian species which had floated across from Australia, but I am highly dubious about that.


Ian Fraser said...

I would guess C equisetifolia, which has been widely planted around the world. They're not geared to oceanic travel.

Kath H said...

Sorry Ian, I didn't try the link because it wasn't a coloured word. But it works fine and brings up Kurrajongs & Bottle trees etc. I felt a bit silly... And of course my comment should have read and how saltbush, not near saltbush.

Ian Fraser said...

Absolutely no apology required Kath. I have no idea why it wouldn't show as a highlit word on your software, but in that circumstance I'd have missed it too. Who understands the wretched beasts that we've so come to rely on?!