Tasmanian Plants

Students of mosses (muscologists) have their agendas to see the Globe Moss when they come to Tasmania.  For students of liverworts (a.k.a hepaticologists), Tasmania houses yet another bryological treasure – a genus of liverworts known as Treubia.

Worldwide, Treubia has consists roughly 6 members of a largely southern hemispheric distribution. Proudly, Tasmania has two members of Treubia, T. tasmanica and T. lacunosa. These are among the most unmistakable of liverworts. Ironically, the appearance of Treubia has puzzled bryologists for decades since famed plant morphologist Karl von Goebel described the genus in 1891.

Liverworts in general, can be divided into two broad groups based on their appearance. These are thallose liverworts with flattish bodies without clear stems or leafy liverworts, which usually have clearly defined stems and leaves.

Treubia on the other hand doesn’t fit very well in either. It would not be too accurate to claim that Treubia has a stem. That would mean it is thalloid. However, from this ‘thallus’ arises many flaps of what look like leaves.

Tasmania’s very own early bryologist Leonard Rodway said of  Treubia tasmanica in 1911:

Many authorities try to avoid the breaking down of established systems by treating the lateral expansions as lobed portions of lateral wings. This seems a distorted description of the apparent structure, and does not tend to a clear understanding of the evolution of the hepatics.

Some bryological giants like Rudolf Schuster and George Scott interpret Treubia to be the midway point between the primitive thalloid way of life in liverworts to the more advanced leafy upgrade. To draw an analogy with animals, Treubia would be to liverworts what velvet worms (Onychophorans) are to invertebrates.

How does this ‘halfway house’ theory fit in with what is known of the molecular phylogeny of liverworts?

Molecular work has shown Treubia to be one of the most basal groups of liverworts, related to yet another morphologically enigmatic group of liverworts of the genus Haplomitrium (which incidentally is alleged to occur in Tasmania as well). Together, Treubia and Haplomitrium form a group that diverged early from the the course of the liverwort evolutionary stream.

Lending strong support to the antiquity of Treubia is the fossil record, with Treubia-like fossils being among the earliest liverwort fossils known. Treubia can really be considered to be a ‘living fossil’ like the Wollemi Pine.

In my interpretation, the leaf-like morphology of Treubia is hence an innovation of it’s own and not an attempt to bridge the thalloid to leafy condition. Could the Treubia lineage then represent an independent attempt to make leaves?

We may not live to see the descendants of the Treubia lineage, for bryophytes features in general do not evolve very fast. But still, Treubia remains a reminder of the innovation and possibilities that even the ancient can strive toward. It is indeed a liverwort that that epitomizes the legacy of Gondwana!

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 Coral Heath (Epacris gunnii) is a fairly common shrub that may be found in wet heath to highland plateaus. This ornamentally attractive plant has heart-shaped leaves with a pointed tip and in it’s full flowering glory produces in a spike-like fashion, numerous flowers in the leaf axils.

In the Royal Tasmanian Botanical Gardens there are many cultivated plants of the Coral Heath, and in particularly, a double form that produces small Camelia-like flowers.

Even though I had the prior awareness the aberration of genetic mechanism of these double form plants, I was still pretty surprised when I stumbled on this strange phenomena of seeing a branch produce a ‘flower’, consisting of a whorl of petals, and have a new shoot growing out of the whorl of petals.

Just to be sure I even sliced the stem and ‘flower’ longitudinally to make sure and indeed, the new shoot just grew continuously out of the whorl of petals.

It is almost as thought the plant decided to make a flower but got sidetracked at the last minute and continued with vegetative shoot growth.

Makes one think, what exactly are flowers?

Many botanists must have pondered on this question.

Thankfully we have some theories.

Thus we learn in botany that flowers consists of four whorls of floral parts in the following order: sepals, petals, stamens (male parts) and carpels (female parts). All flowers are technically modifications of this scheme. And these whorls, some might be surprised to know, are actually modified leaves.

What might come as an even bigger surprise is that the theory of flowers being modified leaves was actually conceived over two centuries ago in the brilliant mind of Johann Wolfgang Goethe, the famous German poet and philosopher.

Goethe, in 1790, had no way of knowing the action of genes in the onset of flowering but his powers of observation would put many a scientist to shame. His insights were discussed his very aptly titled essay, Metamorphosis of Plants.

The concept of flowers being modified leaves might seem very abstract, particularly given the fact that flowers seem to be so different from leaves.

But therein lies the genius of plants. They transmutate. They morph. They make flowers from ‘leaves’. And here it seems our aberrant Coral Heath, leaves from flowers.

Glasswort (Sarcorcornia quinqueflora) with flowers. Lauderdale, Southeast Tasmania.

In 2004 I encountered some strange growths on the glasswort (Sarcocornia quinqueflora), a common saltmarsh plant of the Amaranth family (Amaranthaceae) in Southern Australia and Tasmania.

Knowing little of the glasswort, I thought the structures were it’s succulent fruits. It was a few years later after I had encountered the phenomenon a couple more times that it started to occur to me that those structures might be galls. Winifred Curtis in the Student’s Flora described the phenomena as follows:

‘…short lateral branches or small groups of segments…enlarged and bright red in colour, superficially resembling flowers.‘

This was hard to believe as my impression of galls were deformed lumps on leaves or twigs that disfigured the overall appearance of a plant. The galls on the glasswort on the other hand had a symmetrically beautiful form, with tightly overlapping succulent scales forming a pegoda-like structure.

A quick search online brought me to the profile page of Dr Anneke Veenstra from the Deakin University. In 2007, she and co-workers published a paper on the minute gall midges that were the cause of the flower-like galls on the glassworts. They described the gall midge as Asphondylia floriformis, classed under the Cecidomyiidae, a family under the large order of Flies (Diptera). The specific epithet ‘floriformis’ alludes to the flower-shaped appearance of the galls.

Asphondylia floriformis galls on glasswort shoots. Australian $2 coin (c. 2cm diameter) for scale.

How the galls are formed has yet to be studied in detail but presumably this happens in spring when the adult gall midge deposits an egg via it’s ovipositor into the plant tissue. A local swelling then arises. The larvae of the gall midge then develops in a chamber of the gall. The chamber walls are also observed to develop a covering of fungal mycelia (threads), which I suspect might play some role in the development of the gall midge larvae. When mature, the gall midge makes it’s way out of the top of the gall and leaves behind the cocoon covering.

Gall sectioned to show inner chamber. The remains of the Asphondylia gall midge pupal skin is evident on the top of the gall.

Interestingly, glasswort plant collections with galls date back to the mid 19th century. The first known collection of the glasswort with galls on them was made in 1859 by German-born doctor and botanist Hermann Beckler in Hastings River, New South Wales. Since then, there have been numerous glasswort collections with galls from various Australian states, including Tasmania.

From the notes accompanying the collections, it is evident that some of the early collectors did not recognize the galls and thought they were floral parts. Another thought the galls to be vegetative plantlets that would eventually fall off to establish new plants. I imagine that some of these early collectors did not think that the swellings were galls because it’s ‘natural’ and aesthetic look.

In it’s normal, healthy state, the glasswort is by no means a highly adorned plant. The inconspicuous flowers are borne on fleshy spikes that look just a little more compact than the normal segments that make up the glasswort’s succulent body. Functionality and simplicity is it’s style. But when dealing with an attack from a natural parasite, the glasswort reveals it’s somewhat macabre capacity for morphological aesthetics. Few other plants can claim to have the gall to be beautiful.