THE LICHEN FLORA OF TASMANIA

Gintaras Kantvilas ¹

Introduction

With an estimated 1500 taxa, many of which are yet to be discovered, identified or formally named, lichens represent a very significant part of Tasmania’s biodiversity. In most Tasmanian habitats or vegetation types, lichens will easily outnumber the other terrestrial plant groups (flowering plants, conifers, ferns and their allies, and bryophytes). They range from below the high tide mark on coastal rocks to the tops of the highest mountains, and can colonise almost any surface, including the bark, wood and living leaves of trees and shrubs, rocks, soil, bryophytes, dead or decomposing plant matter, and a whole range of man-made substrata such as concrete, bitumen, glass, metal and rubber. Some even grow submerged in fast-flowing creeks and shallow tarns. Indeed, there is a hardly a habitat where at least some lichens will not be present.

What is a lichen?

Strictly speaking, and certainly from the perspective of the professional taxonomist, lichens are not plants, but an association between a fungus (usually an Ascomycete or “cup fungus”) and either a green alga or a cyanobacterium (termed the photobiont). The association is mutually beneficial and is called a symbiosis. Typically, the fungus dominates the association and provides a stable setting for the photobiont to live. In turn the photobiont photosynthesises, and provides the fungus with a critical food source. For the fungus and most lichen-forming algae, the symbiosis is obligatory and neither occurs in the free-living state.

In its simplest form, a lichen consists of one species of fungus associated with one species of photobiont. However, more complex examples also occur, where a lichen fungus is associated with two different photobionts, or a lichen involves a second fungus, usually growing as a parasite. There are also cases where two fungi and two photobionts are involved, with essentially one lichen species invading the body (called the thallus) of the other. Recent research suggests that further micro-organisms such as yeasts or bacteria may also be involved. Thus a lichen, although outwardly behaving as a simple organism, is actually a complex mini-ecosystem.

Notwithstanding the complexities of this symbiotic inter-relationship, the taxonomy and nomenclature of lichens is based on the fungus and, in modern accounts, lichens are classified within the fungi. Perhaps fortunately, whole genera, families and even some higher ranking groups of fungi are either entirely lichen-forming or not, but at the same time, there are a few taxonomic groups that contain both lichens and non-lichenised fungi.

In practice, and perhaps chiefly because of their superficial appearance and functional ecology, lichens tend to be collected, recorded and studied by botanists rather than mycologists. They also are commonly included in floristic accounts and Floras, although strictly speaking they are not flora but mycota.

Previous accounts of lichens in Tasmania

No comprehensive systematic account of Tasmania’s lichens exists, although the literature pertaining to particular taxonomic groups or to the species composition of particular places or habitats is extensive. The first, and indeed only, attempt to include lichens in a Flora of Tasmania was by Joseph Dalton Hooker in his monumental Flora Tasmaniae (published 1855–1860). Hooker studied most plant groups, and his colleagues Churchill Babington and William Mitten provided him with an account of the then known lichens. Although including only 93 taxa, Hooker’s flora remains the sole milestone in the aspiration to document all of Tasmania’s flora in a single work. An exception is the massive Flora of Australia series (1981–present) where a large number of genera and families that occur in Tasmania are treated in the five lichen volumes.

The author has been working on Tasmanian lichens since 1980 when he commenced a floristic and ecological study of the Tasmanian rainforest lichen flora. Over succeeding decades, the focus of research shifted to the systematics of the flora. A Lichen Flora that brings together all the available information on Tasmanian species into a single work has been a long-term goal.

Arrangement of this Flora

The classification of lichens at family level and above has been rather fluid over the last 40 years or so, particularly with the advent of studies on the anatomy of the ascus (the spore-containing structure of the Ascomycete fungi) and, more recently, DNA-sequence data. This has led to the disintegration of many of the old “form” genera which had been based solely on morphological and spore characters. Consequently, the present work is arranged by genera, even if each tranche of accounts published aims for the most part to deal with related genera that may be classified in the same family.

There is an intention to produce a key to genera in the future. However, the ongoing discovery in Tasmania of previously unrecorded genera and species means that, for the present, such a key would be necessarily incomplete. The keys to genera that are published in the Flora of Australia, David Galloway’s Flora of New Zealand Lichens, by Lumbsch et al. (2001) and McCarthy & Malcolm (2004), and in other sources, whilst very useful, are also examples of keys that have been quickly left behind by ongoing advances in knowledge.

All the generic accounts have been compiled de novo and are based exclusively on Tasmanian specimens. Many lichens have broad geographical distributions and feature in floras and monographs from other parts of the world. Whilst these have been consulted when preparing the Tasmanian accounts, simply “borrowing” treatments and data from them has been strictly avoided. Cases where Tasmanian species differ significantly from their counterparts elsewhere in the world are noted, as these may well indicate subjects for future investigations.

Literature cited

The literature for lichens is growing rapidly and it is inevitable that some important references will have been overlooked. A small selection of “key references” (at time of writing) is presented mainly as an entry into the literature, rather than as a comprehensive list.

Synonyms and protologues

With potentially very broad geographical distributions, some lichens have a very extensive synonymy that encompasses names from many parts of the world. Synonymy in this work is restricted to names that have been explicitly recorded for Tasmania. Citation of type specimens is likewise limited to names based on a Tasmanian type specimen. Every attempt has been made to account for all lichen names that have been ascribed to Tasmania in the literature; excluded names are referred to where relevant.

Descriptions

This is a technical work, directed principally at the specialist. Its aim is to summarise the current state of systematic knowledge of Tasmanian lichens which will serve as a foundation for future work. The need for popular books that kindle the interest of the amateur is acknowledged, but that task is deferred to a later date. In the meantime, a richly illustrated guide to the larger lichens (macrolichens) of Tasmanian rainforest is available in Kantvilas & Jarman (1999). Many species of coastal and drier areas are also illustrated in a guide to Kangaroo Island lichens (Kantvilas 2019), a region with much in common with Tasmania. A Checklist of the Lichens of Australia and its Island Territories, containing an extensive photo gallery, has also been compiled by Patrick McCarthy.

Lichens are described using specialist terminology, some of which is relevant to lichens only, whereas other terms are more broadly applied to the fungi generally. In the future, it is intended to produce a glossary of terms to accompany this flora. However, for the moment, the reader is directed to glossaries such as those available at:

• Flora of Australia Glossary—Lichens; and
• British Lichen Society Glossary of Lichenological Terms

Ascospore size is a critical taxonomic character in lichens. Size ranges cited are based on a minimum 50 observations each and presented in the format: 5th percentile–average–95th percentile, with outlying extreme values in brackets. The chemical composition of lichens is also a critical (or at least very useful) taxonomic character. Chemical data are derived by thin-layer chromatography using standard methods (Orange et al. 2010). Results of spot tests with the standard reagents, 10% KOH (K), commercial bleach such as “White King” (C), KC (a combination of K followed by C), and crystals of paraphenylene diamine dissolved in ethanol (P), are given where relevant. In some cases, the fluorescence reaction under long-wave ultra-violet light is also helpful. Iodine, in the form of the standard Lugols solution, is essential for determining the structure of the ascus.

Each description is accompanied by a selection of specimens (usually three) and the herbaria they are housed in. These provide vouchered reference specimens for each species treated.

References