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.

A rather recent trend in molecular science has been to use the technique to extort genes to reveal the history of how a plant has extended it’s geographical distribution throughout time.

I have written about how researcher James Worth used molecular techniques to pinpoint the locations (refugia) where Myrtle Beeches (Nothofagus cunninghamii) survived during the last glacial period. Just earlier this year, researchers Paul Nevill, Gerd Bossinger and Peter Ades published a paper in the Journal of Biogeography doing the same for the Mountain Ash (Eucalyptus regnans).

As in James Worth’s Myrtle Beech study, the researchers looked for variations at specific locations in the chloroplast DNA in Mountain Ash individuals distributed throughout the species natural geographical range. Different individuals may exhibit specific sequences which may differ from region to region and these are known as haplotypes.

A large amount of haplotypes found in a population an any given area would suggest that the area is a glacial refugium as we would expect a species to have persisted for longer periods of time in a refugium, thereby accumulating genetic changes. Conversely, places with low diversity of haplotypes could be construed to have been colonized after the glacial period ended, as there wouldn’t have been time enough for a high diversity of haplotypes to develop.

The results of the study showed that Mountain Ashes of the Northeast and Southeast of Tasmania has a high diversity of haplotypes, many of which were unique to the region. This suggests that the Northeast and Southeast of Tasmania harbored refugia that sheltered Mountain Ashes during the glacial period. By contrast, the central parts of Tasmania had a lower diversity of haplotypes. Another way of interpreting this was that there was fixing of haplotypes in that region, suggestive of a more recent colonization of the area following the end of the glacial period.

One consideration that remains to be addressed is the ease with which Eucalypts hybridize. E. regnans for example may hybridize with E. oliqua (Stringybark) and E. delegatensis (Gum-topped Stringybark). Hybridization may result in chloroplast sharing between species and a more comprehensive study will probably be needed to ensure that all these factors are taken into consideration.

For now it seems we are getting closer toward reading the the silent tale of survival that the ancestors of the Mountain Ashes in the Northeast and Southeast have etched in the genes of their descendants.

In Tasmania’s heaths, herbfields, cliffs, lake margins and among cushion plant communities of the Northwestern and Central highlands lurk one of Tasmania’s most elusive botanical secrets – a little lily that hails from a botanical lineage of great antiquity.

First though, we must clarify what exactly is a lily.

The natural history and taxonomic relationships within the large family of lilies (Liliaceae) often vexed botanists in the pre-molecular age. After botanists became well accustomed to assigning the appellation of ‘lily’ to a great many species of plants, the molecular blade swiftly and decisively ended the empire of the the lily family. Asparagus (Asparagus spp.), the onions (Allium spp.), the pineapple lilies (Astelia) etc.,  became allied to other plant Orders (as will be elaborated in another post!).

Some of the remaining members of what was once the Liliaceae still remain in what is considered an Order of Lilies, the Liliales. However, the members of this once colossal lily family grouped into smaller families of their own.

One family of lilies, the Campynemataceae, is of paramount interest. Molecular work based of the gene sequences of the RuBisCo enzyme (rbcL) that is present in the chloroplasts of all plants, tells us that the Campynemataceae lineage is the oldest among all that can still be considered a part of the great lily order. In 2004, researchers Thomas Janssen and Kårl Bremer compared the rbcL sequences of representatives of the families in the Lily Order and estimated the Campynemataceae lineage to have come into existence some 117 million years ago, as a sister group to all other families of the Lily Order.

The lily I have deemed to be one of Tasmania’s most elusive botanical secret is Campynema lineare (Green Mountainlily), a representative of the Campynemataceae.

C. lineare is endemic to Tasmania and is the only species in its genus, and Campynema is one of the two genera in the family. The only other members of this family is a genus of three species, the Campynemanthe, that hails from New Caledonia.

C. lineare is a slender herb up to almost half a meter in height, but usually much smaller in highland areas. The leaves are linear as the specific epithet ‘lineare‘ suggests’ but highly inconspicuous when the plant is not in flower. The blossoms are scarcely 2 cm across, with yellowish-greenish floral parts, borne on a brownish stem. This combination does not help in making it stand out well from the surround vegetation. Before releasing pollen however, the bright orange stamens do stand out quite clearly against the greenish floral parts, but in most other respects, C. lineare is a rather inconspicuous plant and not largely different from what anyone would call a ‘lily’.

A casual observer would not have guessed that it is a relict of ancient lilies. Probably not even Jacques Labillardière, the french botanist who described the genus in 1805, guessed that he was beholding a botanical gem.

But the time of awareness is nigh. In this digital and molecular age, inconspicuousness can no longer be an excuse for the lack of recognition suffered by this marvelous plant. It is time for the little Green Mountainlily to take it’s rightful place among the ranks of Tasmania’s iconic plants. Like the Delicate Laurel (Tetracarpaea tasmannica), we must sometimes know of the historical significance of such plants before we can truly appreciate their contribution to botanical heritage of this land we call Tasmania, a home to plant lineages of great antiquity.

When ardent students of mosses or bryologists traverse the globe to come to Tasmania, they will have, among the top candidates of their ‘to-see’ list, an `endemic Tasmanian moss. This is none other than Pleurophascum grandiglobum.

Rest assured that this moss lives up to it’s grandiose name. As this moss is so distinctive and significant, I’ll take the liberty to call it the Globe Moss, a name that I will use henceforth.

The moss was first described by Sextus Otto Lindberg in 1875, an early bryologist, in the Journal of Botany. He wrote (annotations in parentheses mine):

‘I Have to-day received from my friend Baron F. von Mueller, the renowned Director of the Botanic Gardens of Melbourne, a small tuft of a Moss, gathered this year by Mr. Robert Johnston on turfy soil near Picton River, in Tasmania. This Moss is of the highest importance, indeed of no less interest to the Muscologist (moss specialist) than is Rafflesia or Welwitschia to the Phanerogamist (higher plant specialist). It is, in fact, a very robust Phascaceous (bud-like) plant with the fruit perfectly lateral on the stem! I dare not as yet call it truly pleurocarpous (fruiting from specialized side branches), as its affinity is most obscure; but as it has, as far as I know, not been described, it ought to be called Pleurophascum grandiglobum…’

The Globe moss appears to be largely restricted to Buttongrass sedgeland habitats in the western part of the state. In a sterile state, the leaves are beautifully and symmetrically arranged around the stem and from the top look like the way lotus petals are arranged around their flower axis. The leaves are almost cup-like, lack nerves, but usually, although not always, have a single hairpoint at the apex. These characters, with the additional habitatual context, renders the Globe moss difficult to mistake for anything else.

When this moss is in fruit however, it is most unmistakable! The green spherical capsules, which ripen a dull yellow-brown, are 3-6mm in diameter, and are possibly among the largest, if not definitely the grandest, of all mosses in Tasmania. These grand structures that gives the moss it’s specific epithet ‘grandiglobum‘ are borne proudly on long setas (or stalks).

The capsules are cleistocarpous, a sophisticated way of saying that it does not open regularly through a well defined mouth, but rather, splits open irregularly at maturity. Precious little is known about the dispersal mechanism of the spores, much less on why the moss appears to be restricted to Buttongrass sedgeland habitats.

There are other reasons as to why the Globe moss is of such botanical interest. The distribution of the members of Pleurophascum are highly disjunct. One species P. ocidentale occurs in Western Australia. Another species, P. ovalifolium, occurs in New Zealand and was only recently determined by Australasian bryologists Alan Fife and Paddy Dalton in 2005 to be a different species from P. grandiglobum.

The affinities of Pleurophascum to other mosses are unclear. Bryologists have variously proposed that it is related to the Bryum (the Bryaceae) or Pottia (the Pottiaceae) mosses, but until more convincing evidence surfaces, it is best that the Globe moss remain in a family of it’s own, the Pleurophascaceae.

If there should one day be an international exhibition of mosses, where every country were to submit a portraiture of a unique indigenous moss for exhibition, there can be little doubt that the Globe moss will be the prime candidate to represent Tasmania’s bryological heritage. As far as mosses go, the Globe moss puts Tasmania on the world map.

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.

An unassuming daisy, the Yam Daisy (Microseris lanceolata) or ‘Murnong’  as it is known by tuber hunting aborigines on the mainland, has a convoluted history. This makes it a subject of ecological and evolutionary interest to biologists.

It’s closest relatives are found in western North America. Based on morphological and chromosome studies, the Yam Daisy probably came about by the hybridization of two American species followed by long distance dispersal – quite a distance I might add. So it goes that aborigines were eating foods of American origin way back.

This marvelous feat of intercontinental dispersal has been confirmed more recently by studies using DNA extracted from the chloroplasts (cpDNA) of American and the Australian/New Zealand species of Microseris (Vijverberg et al. 1999).

Since establishing in New Zealand or Australia, the Yam Daisy has diversified morphologically into 4 ecological types (ecotypes) – a coastal and fine pappus form in New Zealand and Tasmania, a lowland tuberous form on the mainland and south Australia, and an alpine form in southeast Australia.

One would expect there to be great genetic differences between these morphologically distinct ecotypes. However, another study (Vijverberg et al. 2000) using a sophisticated molecular technique called Amplified Fragment Length Polymorphisms (AFLP) shows that on a molecular level, these four ecotypes of the Yam daisy show surprisingly little differentiation.

Simply put, the lesson that the Yam Daisy imparts is that looking different on the outside (morphological variation) as a result of environmental molding may have little to do what goes on inside (genetic differentiation). Could this be a metaphor for the human race as well?