Tasmanian Plants

I have deep respect for ferns living in harsh conditions and one such fern is  Asplenium obtusatum (Shore Spleenwort). This species is also present in New Zealand but the Tasmanian form is known as A. obtusatum subspecies northlandicum, a form that was described by the renown pteridoloist Pat Brownsey in 1977.

The Shore Spleenwort is allegedly common and grows on rocks along the coastline of Tasmania. Widespread as it is, I’ve only had the fortune of observing it growing on the cliff faces around the Remarkable Cave in the Tasman Peninsula and in the fernery of the Royal Tasmanian Botanical Gardens.

The fleshy and shiny fronds of this fern makes it instantly recognizable and reminds me of the Sea Spleenwort (Asplenium marinum) of the Northern Hemisphere, a fern I would very much like to meet. Being ferns of such similar habitats, I imagine some convergent evolution in form is at work here.

Asplenium obtusatum is tolerant of some salt spray, a remarkable feat indeed given the vulnerability of ferns during the earlier stage of their life cycle.

This earlier stage are known as the gametophyte phase, as opposed to the sporophyte phase that we call ‘ferns’. The gametophyte is an inconspicuous little liverwort-like a structure that germinates and develops from fern spores. In most botany textbooks the fern gametophyte is portrayed as a heart-shaped structure and is called the prothallus. It is from the prothallus that the male and female reproductive parts develop. When the time is ripe for fertilization, the sperm swims through a film of water to find an ‘egg’ to fertilize. From this union, a baby fern is born, growing out of the tissues of the prothallus. The cycle is complete.

Unlike flowering plants, the fertilization of ferns require a film of water as mentioned above. Imagine the physiological stresses that a fern prothallus has to endure when the occasional salt spray comes into the picture!

The Shore Spleenwort is indeed a hardy fern worthy of a lofty station by the magnificent cliffs of the Tasmania coast!

A three-headed manfern (Dicksonia antarctica) found in Northwest Tasmania! Of all places, it was found growing as a cultivated specimen at the carpark of Bischoff Hotel, Waratah, Northwest Tasmania.

This 1.5m or so tall monstrosity of a manfern reminded me of Cerberus of Greek and Roman mythology, the monster usually depicted with three heads which guards the gates of Hades.

Plants like tree ferns usually tend to be single trunked as they only have a single growing axis, pretty much like the majority of palm species.

A perusal through The Ferns of Tasmania by Michael Garrett provided an explanation. Michael is a prominent Tasmanian pteridologist and commercial fern grower. He notes in his book that:

Multiple crowned specimens are commonplace, most often resulting from where several sporelings have grown together with the same vigour.

Now I look forward to seeing a ‘hydra’ manfern!

The number of visits one makes to the Saturday Salamanca market is inversely proportionate to the duration of time one spends in Tasmania.

Yet, after five years in Tasmania I was delighted to stumble upon a store in the market run by Christo Lees, which showcases a fascinating caveat of Tasmania’s botanical heritage, something that I had failed to notice all this while.

These petrified trunks, chalcedonic in nature, were found at Lune River down near the southernmost tip of Tasmania. The sections are believed to date to 165 million years back.

There is a fabulous publication Occurences of gemstone minerals in Tasmania available online, which sheds some details on the fern flora at the Lune River location during the late Jurassic to early Cretaceous.

Fabulously preserved specimens were found there, showing beautifully and clearly the vascular details of the caudex (or trunk), and allowing paleobotanists (botanists who study fossils) to discern at least 11 species of arborescent (tree-like) ferns belonging to 3 genera.

The largest of these genera is Osmundacaulis (Osmundaceae) of which 8 species have left petrified remains at the Lune River. These fossils are world famous fossils among collectors and lapidiarists. They are often distinguished by the distinctive C-shaped vascular strands belonging to petioles (leaf stalks) that surround the central stem.

Closeup of Osmundacaulis jonesii petrified trunk section. Vascular details showing the C-shaped vascular strands.

Given this information, I suspect that the sections in Christo Lees store are from Osmundacaulis. A famous fern of this family is the Royal fern (Osmunda regalis) from Europe, America and Asia. However the true closest modern day living relative of Osmundacaulis in Tasmania with a comparable stature would be the Southern Kingfern (Todea barbata).

Todea barbata (Southern Kingfern)

Todea barbata, while not exactly a tree fern, has a thick trunk and can become treefern-like. A true ‘King’ in stuture! I have had the pleasure of seeing a robust and healthy population of some rather large Kingferns at the base of the Blue Tiers.

I imagine that if civilization still exist and still indulges in the study of paleobotany in 165002009 AD, they might find Kingfern fossils in what they might call the Blue Tiers fossicking site. For now however, it is a pleasure to know that ‘imperialism’ in ferns live on in the form of Todea, and that their ancestry is beautifully captured in the jewellery of Christo Lees.

More links

Geological setting of Jurassic plant fossils near Lune River

The 23th Dec 2008 marks my first visit to the famous Cataract Gorge, Launceston. It’s almost shameful that I lived on this beautiful island for 4 years before paying the gorge a visit.

As I didn’t have much time I merely took a short walk  along the tourist track. The first thing that struck me botanically was the the exuberance of exotic ornamentals. There were whole colonies of  Red Velerian or Kiss me Quick (Centranthus ruber), Blue Periwinkle (Vinca major), Blackberry (Rubus fruticosus aggregate) and more.

By way of native plants, I was most delighted to see the Common Raspfern (Doodia australis). This would be be the first time I am seeing this fern growing naturally.

Also, I was struck by the preponderance of a native moss, Rhacocarpus purpurascens, growing on boulders there. This moss is more often found growing in alpine tarns (see my post on this moss).

My honours project supervisor, Paddy Dalton, told me that he collected this moss in fruit once for this locality. Personally, I’ve seen it scores of times on Mt Wellington but I’ve never seen capsules. Could there be something interesting going on here?

I’ll be back for another visit sometime.