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!