I collect she oaks (Casuarinaceae). This is a recent obsession and I don't have very many species ... so far. Three species of Casuarina and nine of Allocasuarina sit in pots outside my back door. Only another 80-something more if I want to collect the set. (I don't know what happens then. Maybe I get a free set of steak knives.)
When I visited one of my favourite native plant nurseries, Kuranga in Mt Evelyn, a couple of weeks ago, I was delighted to find beautiful specimens of the Daintree Pine (Gymnostoma australianum L.A.S. Johnson, 1980) for sale. Despite its commercial name, G. australianum is not a conifer. It belongs to Casuarinaceae, along with my other favourites. Of course, I bought one.
So why call it a pine if it's not a conifer? Well, it looks a bit like one because like many pines, Gymnostoma appears to lack leaves. They do have them. It's just difficult to spot the leaves if you don't know what you're looking for.
If you examine a branchlet from Gymnostoma (or any other genus of Casuarinaceae), you'll see that it is made up of a series of sections, joined end to end. Each section is called an article. Ridges (phyllichnia) run lengthwise along the articles, giving them a grooved appearance. Now, if you can see the phyllichnia, you will be able to see the whorls of tiny leaves that sit around the junctions between articles. They don't do much, but they're definitely there.
They also look like pines because they produce cones. But unlike those of conifers, the cones of Gymnostoma and relatives develop from fertilised flowers.
Anyway, I suspect commercial growers use that name because of the popularity of the Wollemi Pine (Wollemia nobilis Jones, Hill & Allen, 1995). The advertising blurb certainly pushes the Gondwanan origin. (It says Gondwanaland, which is a tautology. Gondwana means 'land of the Gonds'.) Although the eighteen living species of Gymnostoma are restricted to Queensland, New Guinea, Fiji and New Caledonia, fossils have been found in other parts of Australia and in New Zealand, Argentina, South Africa. That's a Gondwanan distribution, if ever I saw one.
Studies suggest that the Casuarinaceae appeared around 70 million years ago (just a short time, geologically speaking, before the end of the dinosaurs). Gymnostoma is the oldest of the four living genera. It probably arose between 40 and 45 mya, when Australia was still joined to Antarctica (Crisp et al., 2004).
Ten extinct species of Gymnostoma are known from Australia. Their fossils occur in the Kambalda–Norseman region, Western Australia; at Lake Bungarby, New South Wales; Little Rapid River, Tasmania; and Mount Hotham, Victoria (Carpenter & Pole, 1995; Scriven & Hill, 1995; Hill & Guerin, 2003; Carpenter et al., 2004). During the Cenozoic, this genus occupied most of the continent, thriving in warm, humid conditions similar to those in the modern wet tropics. Then Australia moved northwards, completing its split from Antarctica and becoming drier as the ocean circulation patterns changed. Rainforests declined and the arid-adapted vegetation took over.
Now G. australianum is the only extant Australian species in the genus. It occurs in the Daintree district of Far North Queensland. Its total range is no more than a few square kilometres—if that—centred on Thornton Peak in the Wet Tropics World Heritage Area. Although its distribution is limited, Prider and Christophel (2000) recorded populations growing on rocky creek banks, granite outcrops and in fern fields. According to the advertising, G. australianum is a tough bugger. (I'm paraphrasing, you understand.) I'd say that was a pretty accurate assessment.
Read more
Carpenter, R.J., Hill, R.S., Greenwood, D.R., Partridge, A.D. & Banks, M.A. (2004). No snow in the mountains: Early Eocene plant fossils from Hotham Heights, Victoria, Australia. Australian Journal of Botany 52(6) 685–718.
Carpenter, R.J. & Pole, M. (1995). Eocene plant fossils from the Lefroy and Cowan paleodrainages, Western Australia. Australian Systematic Botany 8(6) 1107–1154.
Crisp, M., Cook, L. & Steane, D. (2004). Radiation of the Australian flora: what can comparisons of molecular phylogenies across multiple taxa tell us about the evolution of diversity in present-day communities? Transactions of the Royal Society of London, Series B 359: 1551–1571.
Hill, R.S. & Guerin, G. (2003). Gymnostoma tasmanianum sp. nov., a fossil Casuarinaceae from the Early Oligocene of Little Rapid River, Tasmania, Australia. International Journal of Plant Sciences 164: 629–634.
Prider, J.N. & Christophel, D.C. (2000). Distributional ecology of Gymnostoma australianum (Casuarinaceae), a putative palaeoendemic of Australian wet tropic forests. Australian Journal of Botany 48(4): 427–434.
Scriven, L.J. & Hill, R.S. (1995). Macrofossil Casuarinaceae: their identification and the oldest macrofossil record, Gymnostoma antiquum sp. nov., from the late paleocene of New South Wales, Australia. Australian Systematic Botany 8(6) 1035–1053.
