Sunday, 5 May 2013

Antarctica in Riddells Creek

Dicksonia antarctica that is, Soft Tree Ferns. 

Conversations with RCL member Robert Blair revealed that he had tree ferns on his property, high up on Gap Road. So I had to investigate further! Robert kindly took me on a walk up to the headwaters of a small Sandy Creek tributary that, these days, appears to rarely see flowing water. And sure enough, there it was, but only one remaining alive (plus one that had recently passed away but only time will tell if it springs back to life).

It seemed obvious that this one had only survived because its trunk (left) was growing in a deep hole that was likely to trap water.

Excitingly though, we also found one other living tree fern further down the same creek line and this turned out to be a different species, the Hard (or Rough) Tree Fern, Cyathea australis. This was easily identifiable from a few spores that remained on the underside of the fronds.

Dicksonia antarctica, Soft Tree Fern, is perhaps the most iconic of the Australian Tree Ferns can grow to15m tall, grows no more than 5 cm per year and produces spores after about it reaches about 20 years old.

And of course they reached Riddells Creek many millennia ago, ferns being among the most ancient group of plants.

The two species often grow together and are similar in their habit. There are two good ways to tell them apart. First, the spores are very different in appearance if you are lucky enough to see them. Earlier this year I saw both in spore at the same time at Lake Elizabeth in The Otways. The photo below is Dicksonia antarctica, Soft Tree Fern, with its pustule like spores.
... and below is Cyathea australis, Hard Tree Fern, from Lake Elizabeth.

If they aren't in spore (as is often the case) then the trunk and base of the fronds is the key. In young plants you will often have fight through the old fronds to reach the trunk but in old, tall plants the trunk is easily seen. As the trunk grows the base of the fronds remain and cover the trunk. In the Hard/Rough Tree Fern the old frond bases are very hard and 'prickly' (press them and they don't compress at all) and they are surrounded by hard, greyish string/hair-like structures. In the Soft Tree Fern the frond bases are soft (press them and they will collapse/break) surrounded by soft, reddish-brown hairs. Here is trunk of the Soft Tree Fern:

... and here is the trunk of the Hard/Rough Tree Fern:

They are magnificent in rainforests, reaching great heights and they can occasionally be seen like this in the Macedon Range, but many populations struggle to reach great heights. As at Robert's place, these plants will struggle as areas dry out.

Finally, Robert is of Scottish heritage and so may be interested in the derivation of the botanical name:
Dicksonia - named in honour of James Dickson, 1738-1822, a Scottish nurseryman.
antarctica - 'southern', or from the Antarctic regions.
Cyathea - derived from the Greek kyatheion, meaning "little cup", and refers to the cup-shaped spores on the underside of the fronds.

Here is a lovely Hard/Rough Tree Fern from Lake Elizabeth:

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