Lichens

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A mixture of lichens on a mangrove tree, Huskisson, near Jervis Bay, NSW
Image: M. Fagg, © ANBG

Notes by Heino Lepp

You can go straight to a list of lichen species found in Australian mangroves or you can continue reading this page which gives some general information.

What is a lichen?

A lichen is not a single organism. Rather, it is a symbiosis between different organisms - a fungus and an alga or cyanobacterium. Cyanobacteria are sometimes still referred to as 'blue-green algae', though they are quite distinct from the algae. The non-fungal partner contains chlorophyll and is called the photobiont. The fungal partner may be referred to as the mycobiont. The partnership is very intimate and intricate in the sense that the naked eye sees a single physical entity and to see the separate fungal and photobiont components it is necessary to use a microscope.

Lichens show a variety of growth forms and the most commonly seen growth forms are crustose, foliose and fruticose. Crustose lichens are markedly two dimensional and firmly attached to the substrate by their entire lower surfaces, making it impossible to see a crustose lichen's undersurface. A crustose lichen looks very much like a thin crust on the substrate. Fruticose lichens are erect or pendulous and markedly three-dimensional. Foliose lichens could be thought of as halfway between crustose and fruticose. Though obviously three dimensional they grow in a more-or-less sheet-like form, but often with a lobed appearance. They are not attached by their entire lower surfaces to their substrates. Indeed, some foliose lichens are just centrally attached to their substrates with the rest loose, so making it possible to see both the lower and upper surfaces very easily. The bright orange species of the genus Caloplaca are striking examples of crustose lichens. Usnea is a widespread fruticose genus and Xanthoparmelia a widespread foliose genus.

Many lichens bear distinctive reproductive structures such as disc-like or cup-like apothecia, more-or-less linear lirellae or somewhat dot-like perithecia. Apothecia vary from under a millimetre to over a centimetre in diameter and come in a variety of colours. Lirellae may be several millimetres in length, simple or branched and are commonly black. Perithecia are commonly black, under a millimetre in diameter and pustulate. Incidentally, you will often see the term thallus used in the lichen literature. A lichen thallus consists of the vegetative part of the lichen and so excludes any apothecia, lirellae or perithecia. The following links show some examples of sexual reproduction structures:

Brown apothecia on the yellow-green thallus of Flavoparmelia rutidota.

Black lirellae on the pale grey thallus of Graphis mucronata.

Black perithecia on the green thallus of Strigula smaragdula.

In apothecia, lirellae or perithecia the fungal partners of lichens produces fungal spores by means of sexual reproduction. Photobionts within lichens do not reproduce sexually but lichens are capable of reproducing asexually by means of propagules that contain both mycobiont and photobiont cells. In contrast to sexual reproduction asexual reproduction does not, in general, involve any distinctive structures.

You may come across the terms macro-lichen and micro-lichen. These are two more examples of usefully imprecise terms. Roughly speaking a macro-lichen is one that is foliose or fruticose and the rest are micro-lichens. Note that this has nothing to do with size, despite the impression given by the prefixes macro and micro. A species that typically grows as a foliose form to say a centimetre diameter would be a macro-lichen whereas a crustose species that typically grows to over 10 centimetres in diameter would be a micro-lichen.

There is more basic lichen information on this introductory page of the Australian National Botanic Garden's lichen website.

Identification of lichens

There are genera (and even species) of lichens that are easily recognizable by the naked eye but in general the identification of lichens is based on a combination of macroscopic and microscopic features. In many cases chemical tests may be necessary to ensure correct identifications. The common chemical tests involve the use of one or more of potassium hydroxide, calcium hypochlorite, paraphenylenediamine and Lugol's solution. The first two are readily available. Potassium hydroxide is often sold in hardware stores as caustic potash and many household bleaches contain calcium hypochlorite and, suitably diluted, such household bleaches can be used in lichen work. Paraphenylenediamine is poisonous and Lugol's is an iodine solution.

This photo shows the result of one chemical test.

In the Further reading section of the Australian National Botanic Gardens lichen website you will find an annotated list of identification guides to Australian lichens. People can confuse some non-lichen organisms with lichens and there are some observations about that subject on the What's not a lichen page of that website.

The lichens found in Australian mangroves

Lichens of a variety of growth forms have been found in Australian mangroves but, measured in terms of species numbers, the crustose form is the commonest.

Almost all the species found in Australian mangroves have been found also in other habitats, in many cases well away from mangroves. Certainly there are species known only from mangroves and some may be confined to mangroves. However, some of those species are cryptic and may have been overlooked in other areas. Some, though thus far in Australia found only in mangroves, have been found in non-mangrove habitats overseas, suggesting that they could occur outside mangroves also in Australia. For now, all that can be said is that if there any obligate mangrove-inhabiting lichen species in Australia, the available evidence indicates that there would be very few of them.

The study of the lichens found in Australian mangroves

Mangrove lichens have been reported in a number of publications about Australian lichens. However, most of those reports have been incidental since the focus has been mostly taxonomy rather than mangrove habitats. There have been very few detailed studies into the lichens of Australian mangroves. Moreover, those studies are relatively old and, in the light of taxonomic changes in the years since, some of the conclusions would need to be modified.

The first published account of Australian mangrove lichens seems to have been a very brief paper of 1958 [1] which reported three species, based on specimens collected from the mangroves of Arnhem Land in 1948. The year 1975 saw the appearance of a report [2] of the flora of the Prince Regent River Reserve in the Kimberley region of north-western Australia. Included in that paper was a brief account, by Nathan Sammy, of lichens found in the Prince Regent River Reserve and 16 taxa were reported growing on the mangrove species Ceriops tagal or Rhizophora stylosa. Some of the lichen specimens collected from the mangrove habitats were identified to species, others only to genus. Since that paper was published there have been both a great increase in knowledge of Australian lichens as well as changes in taxonomic concepts. Therefore, in the absence of more information about the lichen specimens collected from the Prince Regent River Reserve, it would be unwise to take those 1975 identifications at face value today. However, one fortunate thing is that for each lichen species reported in [2] at least one specimen is cited by collector and collection number. It is possible those collections are still kept at the Western Australian herbarium and, if so, could be re-examined to have their identifications checked.

Most of the few publications about lichens of Australian mangroves have dealt with the mangroves of eastern or southern Australia. Each of [3], [4] and [5] contained short lists of species but a far more detailed study of the lichens of eastern Australian mangroves appeared in the unpublished M.Sc. thesis by G.N. Stevens ([6]), which gave rise to a published paper ([7]). Some of Stevens' results were also included in [8] and the same authors published a study relating to Moreton Bay ([9]).

To date, Stevens' work is still the only in-depth study of lichens in Australian mangroves. She noted that her study was based on well over 2000 collections, from sites spread over 4000 kilometres of coastline from Cairns in the north to Westernport Bay in Victoria. Specimens were collected by Stevens or here friends or colleagues between 1975 and 1978. In her thesis (pages 14-15) Stevens wrote: "Because of the vast distances to be covered, four extensive trips were undertaken, but in these instances the time factor proved a problem as it prohibited lengthy stops at every location. Also, in some instances high tide coincided with time of arrival at a site, and in such cases sampling was rather restricted. A canoe enabled this difficulty to be overcome at a later date...At most sites a representative sample of lichens was collected but in a few instances only relatively few trees were examined due to limited time or some unforeseen circumstances. However even in these cases the lichens found did give an indication of which species were persisting at that latitude...Crustose lichens were also collected during this study, and it was originally intended to include them with the macrolichens in the investigations, however in view of the difficulties in determination and classification of the large number of species and the lack of modern taxonomic literature, the idea was abandoned".

As with the other studies of the 1970s, Stevens' identifications cannot be assumed to be still valid today, given the changes in lichen taxonomy since then. Many of her specimens are held at the Queensland herbarium and many have been cited in later publications, which have provided revised identifications. hence it has been possible to include some of her findings in this website. However, there must still be many of her specimens that, if re-examined, would expand the list of lichen species known from Australian mangroves or add additional mangrove locations of species already known to occur in Australian mangroves.

The need for more work

If you go to the list of lichen species found in Australian mangroves (see Lichens) you will find over 280 species listed, quite an impressive count. Much of this knowledge as to which species occur in mangroves is a consequence of a considerable amount of field work that has been carried out by lichenologists since the 1970s. However, if you look at the known distributions of these 280 odd species you will find that many are known from just a very few mangrove sites, often within a limited geographic range, whereas they are known from non-mangrove habitats over a much wider geographic range. This suggests that many of those 280 species should be found in many more mangrove areas and therefore there is still scope for a great deal of productive lichen-oriented field work in Australian mangroves. However existing herbarium specimens are also a potential source of additional knowledge. A little earlier I noted the possibility of gains in knowlewdge about mangrove lichens if the specimens studied by Sammy or Stevens were re-examined and I will give another example, better known to me. The Australian National Herbarium in Canberra holds a large collection of Australian lichen specimens, amongst which there are about 600-700 lichen specimens, collected from Australian mangrove habitats, that either have not been identified or have been identified only to genus. Information from none of those specimens has been included in this mangrove website. If properly examined, those 600-700 specimens might provide species additional to the 280 but certainly should extend the mangrove areas of some of the 280 species already listed.

Species list:

The following link will take you to the list of lichens reported from Australian mangroves: Lichens

References

  1. Bibby, P. (1958). Some Lichens collected in Arnhem Land. p. 169 In R.L. Specht and C.P. Mountford (Eds.) Records of the American-Australian Scientific Expedition to Arnhem Land. 3. Botany and Plant Ecology. Melbourne University Press, Melbourne. (more)
  2. George, A.S. and Kenneally, K.F. (1975). The flora of the Prince Regent River Reserve, north-western Kimberley, Western Australia. Wildlife Research Bulletin of Western Australia, 3: 31-68. (more)
  3. Graham, M., Grimshaw, J., Hegerl, E., McNalty, J., & Timmins, R. (1975). Cairns wetlands: a preliminary report. Operculum, Oct 1975, 117-148. (more)
  4. Saenger, P., Specht, M.M., Specht, R.L. and Chapman, V.L. (1977). Mangal and coastal salt-marsh communities in Australia. pp. 293-346 In Ecosystems of the World. Vol. I. Wet coastal ecosystems. V.J. Chapman (ed.). Elsevier: Amsterdam. (more)
  5. Hegerl, E. J., & Davie, J. D. S. (1977). The mangrove forests of Cairns, northern Australia. Marine Research in Indonesia, 18, 23-57. (more)
  6. Stevens, G.N. (1978). Lichens on mangroves along the east coast of Australia. M.Sc. thesis, University of Queensland. (more)
  7. Stevens, G.N. (1979). Distribution and related ecology of macrolichens on mangroves on the east Australian coast. Lichenologist, 11: 293-305. (more)
  8. Rogers, R.W. & Stevens, G.N. (1981). Lichens, pp 591-603 in Keast, A. (ed.) Ecological Biogeography in Australia, Volume 1. W. Junk, The Hague. (more)
  9. Stevens, G.N. & Rogers, R.W. (1979). The Macrolichen Flora from the Mangroves of Moreton Bay. Proceedings of the Royal Society of Queensland, 90: 33-49. (more)

-- EmmaClifton - 2011-07-11