About Me

My photo

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.

Thursday, 6 August 2015

Xanthorrhoeas; the wonderful grass-trees

Well actually they're not grasses, and only ambiguously trees, but Xanthorrhoea is never going to catch on as a common name, and the old name of 'blackboy' (for the supposed resemblance of the silhouette to an indigenous man holding a spear) has no place in today's world. I grew up in South Australia calling them Yaccas, and Balga is often used in the south-west of the country, but these are purely regional and so we seem to be left with grass-tree for now at least. It is evocative though.
Large (and very beautiful) X. glauca along the Mount Kiangarow Track, Bunya Mountains NP, Queensland.
In general the species are not distinguished at common name level, though some are, at least locally.
So, what are these plants that must look pretty strange to eyes that didn't grow up with them? For a start they're monocots, and indeed fall within the broad 'lily' grouping. (For more on lilies, see here and work forward from there.) All 30-odd species are Australian, and all belong to the genus Xanthorrhoea. Traditionally they formed their own family (though if we go far enough back we'll find they've had a convoluted taxonomic history) but modern thinking would include the aloe family Asphodelicaceae and bigger family Hemerocallidaceae (in Australia that incorporates flax lilies, rush lilies, grass lilies etc) as sub-families within Xanthorrhoeaceae.

It is a common misconception that grass-trees are an ancient group but it seems in fact that they are a recent rapidly-evolving genus.

The apparently woody stems possessed by most species are in fact hollow, though contain a fibrous matrix; the meristem, which grows outwards as well as upwards, is surrounded by the woody bases of old leaves which have dropped off as they become shaded out by newer ones above - the characteristic hanging 'skirt' of dead leaves can be seen in the photo above.
These Desert Grass-trees X. thorntonii on the Mereeni Loop Road in central Australia
exhibit the typical rough grass-tree stem, formed by the ends of the leaf bases.
This is the only grass-tree that grows in the central deserts.

Cross-section of grass-tree stem.
Note that in this old stem the inner fibrous material has rotted away - the trunk isn't truly hollow.
See Gregg Muller's helpful comment below on this aspect.
The flower spike, comprising thousands of tiny lily-like flowers, may be several metres high. Flowering does not rely on fire, but is stimulated by it. However it doesn't flower immediately, but in the winter-spring after a summer fire; if the fire comes later in the year the mass flowering may be delayed until the second winter.
X. semiplana flowers Wanilla CP, Eyre Peninsula, South Australia.
 
Unburnt X. glauca flower spike growing by road in Goobang NP, New South Wales.

X. platyphylla flowering in a burnt landscape, Fitzgerald River NP, Western Australia.
Each leaf base protects a growing bud, which starts growing immediately the living leaf is burnt off.

Mass post-fire flowering of X. australis, Brisbane Ranges NP, Victoria.
These flower spikes provide a huge nectar resource when flowering and an unusually wide range of pollinators visit them, from gliders, bats and other mammals at night, to insects, honeyeaters and lorikeets during the day.
Hoverfly Family Syrphidae revelling in the abundant nectar of X. glauca, Goobang NP.

Only a few of the numerous flowers will be successfully pollinated, but this still produces a large crop of hard seeds when the flower spike dries out. 
Seed cases - many of them opened - on  X. semiplana, Wanilla CP, South Australia.
To Aboriginal people, grass-trees were of immense significance. The powdery resin was used for gluing tool heads to handles and as such was an important trade item. The same resin was regarded as an important medicine, and as a lacquer for smoothing and sealing surfaces. Pieces of the flower stalk were rubbed to make fire, and the resin was very flammable, so dried leaves made excellent kindling. The stalks were used as light spear shafts. Grass-trees were also a very diverse food source; edible grubs were found at the base of the plant, the base of the young inner leaves was eaten raw or cooked, the seeds crushed to make flour, and honey was extracted from the flower spike by drawing leaves up the stem, or by soaking it in water for a sweet drink. The fibrous leaves were woven into shelters.
X. glauca overlooking the dry plains of inland south-east Queensland, Bunya Mountains NP.
Europeans processed the resin to make medicines (including, I am intrigued to read, for both diarrhoea and constipation!), perfumes, varnish and explosives; it is said that Germany imported a lot for the latter purpose (based on the picric acid it contains) prior to the first World War. The fibrous trunks were used as brake blocks for steel wagon tyres.
Ancient X. glauca, Bunya Mountains NP.
In case it wasn't clear, I just love grass-trees. They are, to me, quintessentially Australian; however I am delighted, even anxious, to share them with you wherever you're reading this. I hope you can enjoy them too, though there's no substitute for meeting them on their home ground.

BACK ON WEDNESDAY

5 comments:

Flabmeister said...

Your comment about the name Yacca calls to mind orienteering in the Adelaide Hills, especially Para Wirra Recreation Park where there are locations with several acres covered with the plants. Not easy to run through.

For more leisurely viewing I think some of the best specimens I have come across are at the head of the Rainforest Gully in the Australian National Botanic Gardens in Canberra. When in flower they have magnificent spikes .

Martin

Todd McLay said...

Hi Ian,

Great article. I am a PhD student at the University of Melbourne working on evolution of Xanthorrhoea. Recent work by Crisp et al (2014) indicates an age of the Xanthorrhoea crown between 25-35 million years. This age coincides with the expansion of dry environments in Australia, and is found in other groups found in similar habitats, such as Eucalypts, Callitris, and several Fabaceae.

Cheers,
Todd McLay

Mark Simpson said...

Hey Ian,

Love your work. Like you, I am fascinated by these quintessentially Australian plants that are full of paradoxes. Your photographs are awesome!

Thanks for blogging

Mark Simpson

Gregg Muller said...

Hi Ian, nice post. However, one teensy issue - the cross section pic is of a rotted 'trunk' - the fibrous cortex is missing. Might mislead some into thinking they are hollow. Have you looked at the inner surface of the shell? usually has longitudinal waves that probably relate to annual growth spurts - a possible way to age dead grasstrees.

Ian Fraser said...

Hello Todd, Mark and Gregg and thank you for your kind and helpful comments. Unfortunately they all arrived just after I left for South America, hence the delay in this response - I hope you see this. I'd not seen Crisp's work Todd, and am most grateful to you for bringing it to my attention. Gregg, I've amended the caption of the trunk cross-section to draw readers' attention to your clarification.