Tasmanian Plants

It is most remiss of me, that I should write of one of Tasmania’s most iconic trees only now, after more than a year of blogging about Tasmania’s fantastic flora.

Introducing a tree that needs little introduction – Tasmania’s one and only deciduous native tree, the inimitable Nothofagus gunnii, the Deciduous beech, the Tanglefoot. There are those too, who simply call it the Fagus.

The Deciduous beech is a small tree from the beech family (Fagaceae). It reaches little more than 2 meters at the slightly lower altitudes but practically sprawls over boulders in the alpine zones. It is a mere dwarf compared to it’s much more widespread relative, the Myrtle beech (Nothofagus cunninghamii).

The legacy of the Deciduous beech however predates that of the Myrtle beech. As far as geological time is concerned, the latter is a much younger player in the biogeographical game.

Fossils very similar to that of the modern day Deciduous beech have been found in Antarctica, which leads one to conclude
very similar species were in Antarctica before Australia separated from that now snowed out landmass.

The deciduous nature of N. gunnii also leads one to think that deciduous-ness might have been a much more common feature of the Tasmanian tree flora in times past.

Alas, this is not really the easiest plant to visit. The Royal Tasmanian Botanic Gardens (RTBG) has at least one specimen, but it is a small one hardly more than 50cm tall, and it is largely obscured by other plants.

Obscured! That’s criminal, particularly given that an illustration of the deciduous beech graces the signboard at the entrance of the RTBG. Still, that is one of the closest places to civilization that one may visit this icon.

Most understandably, the Deciduous beech must be one of Tasmania’s most difficult-to-cultivate icon. It takes a long time to grow, if it even survives. Still, once it harmonizes with a sincere plants-person, a most exquisite bonsai plant the Deciduous beech will make.

But the connoisseur will seek the Deciduous beech in it’s highest abode. The true seeker must travel to the mountains to the west, during April of the Austral fall. They must drive west bound, up windy beaten roads, through the grand forest of the Mountain Ash. And where the road ends by the Dobson Lake, they must by foot alone traverse boulder and tarn, beyond where the highland gums surrenders to frost and exposure. Then, and only then, does the sincere seeker arrive at the Tarn shelf, a true mecca of nival endemicity, where the deciduous beech basks upon the alpine boulders in it’s most exposed, most brazen magnificence.

And then one may say that one has witnessed the leaf fall of the last of Tasmania’s deciduous, the yellow of the autumn Fagus.

The Myrtle Beech (Nothofagus cunninghamii) is one of Tasmania’s icon trees, and is the dominant component of  Tasmania’s cool temperate rainforest. Where these dendrons attain their finest stature in some parts of Tasmania’s verdant Northwest and Northeast, they assemble grand cathedral or callidendrous (meaning ‘beautiful tree’) rainforests, which has for generations captured the imagination and awe of Tasmanians.

Back 18,000 years ago, when glaciations in Tasmania were at their maximum (called the Last Glacial Maximum and henceforth abbreviated LGM), practically the whole of the island would have been unsuitable for the development of cool temperate rainforest, except in pockets of areas in the west. Such areas where plants survived during glacial periods are called refugia.

In the present day, the Northeastern part of Tasmania has sizeable patches of Myrtle Beech rainforest. Yet, geomorphological and pollen-based data suggests that the entire Northeastern area was too arid during the LGM to support rainforest. The question thus arises whether Myrtle Beech trees had survived there in refugia during the LGM or whether they were dispersed from refugia from the west after the LGM?

The immediate problem with the latter suggestion is that Myrtle Beech seeds disperse poorly over long distances, making it unlikely for seed to cross over 150 km from western refugia.

Tackling this conundrum was the topic of Dr James Worth’s honours research and part of his doctorate studies. The efforts of James and his fellow investigators have culminated in a recent publication in the scientific journal New Phytologist.

From his extensive fieldwork, James collected Myrtle Beech leaves from over 340 trees across the distributional range of the species, which includes both Tasmania and Victoria. Using molecular techniques, James then extracted the chloroplast DNA from these individuals and compared their DNA sequences.

James discovered that a common signature in the DNA (a chloroplast DNA sequence that is called a haplotype) that exists for Myrtle Beech trees in Victoria and in numerous areas of Tasmania. The western part of Tasmania however, had an additional and significantly large suite of other endemic haplotypes, suggesting a complex evolutionary history of Myrtle Beeches in that area, and perhaps survival in numerous refugia, which is within expectations.

Myrtle Beech haplotype distribution. White circles and black circles represent the widespread and endemic western haplotypes in the left and right map respectively. Red circles represent the unique Northeastern haplotypes. MA = Mt Arthur; MB = Mt Barrow; BL = Ben Lomond; MM = Mt Maurice; MV = Mt Victoria; BT = Blue Tiers

In the Northeast, trees from two regions bore the common haplotypes, some in the western extreme (Mt Barrow), and some in the eastern extreme (Blue Tiers). In between was a central region (areas in the vicinity of Mt Victoria, Mt Arthur and Mt Maurice) in which a unique haplotype was discovered.

At least for this central region, the presence of the unique haplotype is strong evidence that there must have been refugia for the Myrtle Beech in that area.

James concluded that the Myrtle Beech withstood the aridity of the last glacial period within multiple regions in apparently inhospitable climates.

Whether cathedral rainforest actually existed in refugia in the Northeast during those times is questionable but if the conditions then were simply untenable for rainforest, Myrtle Beech trees could still have survived, being, as we are currently able to observe, able to occur as a compact shrub in harsh highland environments.

This is where the true virtues of the Myrtle Beech comes to light. If Myrtle Beech did not survive through the last glacial, there would be no rainforest to speak of. Yet, Myrtle Beech did more than just survive through the LGM. Fossils suggests that it has been around for at least 780000 years. Myrtle Beeches have therefore survived through numerous cycles of glaciation.

The resilience of this iconic temperate tree throughout the ages has unquestionably shaped Tasmania’s modern biota.

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 find a store in the market showcasing 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 and are claimed to belong to the manfern (Dicksonia).

However, these petrified sections are not actually man ferns.

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.

The fabulously preserved specimens show beautifully and clearly the vascular details of the caudex (or trunk), 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 the Salamanca 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 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. I have had the pleasure of seeing a nice 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.

As for why the fossil sections were touted as belonging to manferns, I imagine it helps the seller to relate to potential customers. Many people in Tasmania would have heard of manferns but few would know of kingferns. Imperialism is outdated these days.

More links

Geological setting of Jurassic plant fossils near Lune River