1. Lichens

2. Why study lichens?
Important part of Ireland’s biodiversity with ~1,165 species
West of Ireland
very important
Lichens are a huge part of Ireland’s biodiversity with about 1,165 species known. The west of Ireland has some very lichen rich areas containing some rare species for example some woodlands have species of the Lobarion alliance, a group of lichens that includes tree lungwort (Lobaria pulmonaria). This group is usually only found in well-established, relatively undisturbed woodland.
Many lichens are pioneering species and may be the first organisms to colonise bare substrata including soil, as well as rock, before they are out-competed by higher plants on soil. Lichens can physically penetrate the outer crystals of rock and their secondary metabolites (lichen acids) can chemically attack the rock and soil-trapping lichens establish themselves. Thus it creates the conditions for higher plants to establish.
Photo: Maria Long

3. Hawksworth & Rose scale (1970) 0-10 for acid and basic bark
Pollution indicators
Disappearance of lichens led to black (melanistic) form of peppered moth
Hawksworth & Rose scale (1970)
0-10 for acid and basic bark
Some species of lichen are particularly sensitive to pollution and have been widely used in studies monitoring air pollution levels, in particular that of sulphur dioxide in the air.
For example there’s the classic case of lichens disappearing on trees in cities in Britain from the industrial revolution onwards as levels of air pollution rose as a result of increased industry and coal burning. The peppered moth was dependent on the lichens for camouflage but as the lichens disappeared and bark was turned black with soot and ash the melanistic form of the moth began to increase. As you can see in the picture the typical form stands out conspicuously to predators on the blackened bark. Thankfully though as measures to control levels of air pollution have taken effect in the last decades the lichens are returning to the bark and the typical peppered moths are also coming back to cities in the UK.
Due to the large quantity of studies done on lichen species responses to air pollution David Hawksworth and Francis Rose developed a scale from 0 to 10 to estimate the mean levels of sulphur dioxide in the air. They drew it up for epiphytes on both acid and basic (or nutrient-enriched) bark. 0 represents no epiphytes at all (including algae) where you’d have very high levels of pollution, and 10 would correspond to clean air where you’d get only the most sensitive species growing, for example Sticta limbata on acid bark. Other things need to be taken into consideration here though for example, some of the sensitive species may take a while to re-establish.

4. Lichens provide food and/or shelter for animals
Used for dyeing e.g.
crottle
Used in medicine
Used in perfumes &
pot pourri
Lichens provide food and/or shelter for animals
Lichens contain substances known as lichen acids which we’ll talk about later. Many of these have long been used by man.
A very important traditional use of lichens was dyeing. Crottle is a yellow-brown or red-brown lichen dye from Parmelia omphalodes and P saxatilis which both contain salazinic acid.
It has been shown that 50% of all lichen species contain lichen acids that have antibiotic properties for example usnic acid which is found in the genera Usnea and Evernia. This can be found in creams used to treat skin disorders. People used to believe that the creator made certain plants and lichens to look like the body part that it had properties to heal. For example tree lungwort (Lobaria pulmonaria) pictured here was used to treat lung ailments
Evernia species are also used in perfume making and in pot pourri as they can ‘fix’ scents, i.e. scents are absorbed and released slowly over time.
Many lichen species provide food for animals, for example reindeer in tundra areas feed a lot on Cladonia sp. Birds sometimes use lichens to line their nests

5. Under-recorded Year-round activity
Again, like bryophytes, lichens are under-recorded in Ireland so there is plenty of opportunity to increase our knowledge. Again it’s a year-round activity.
Lichens are very slow growing, some species growing only a few millimetres a year, others perhaps less than a millimetre per year. Most are perennial and some may persist for many hundreds of years if in stable environments.
The Irish Lichen Field Club run by Paul Whelan would welcome membership.

6. What are lichens?
A lichen is ‘an ecologically obligate, stable mutualism between an exhabitant fungal partner and an inhabitant population of extracellularly located unicellular or filamentous algal and/or cyanobacterial cells’ (Hawksworth et al., 1995)
A lichen is ‘a stable self-supporting association of a fungus (mycobiont) and an alga and/or cyanobacterium (photobiont)’ (Hawksworth et al., 1995)
1860s – Simon Schwendener – true nature of lichens
‘..the unnatural union between captive algal damsel & tyrant fungal master’ Crombie, 1874
A lichen is a composite organism made up of a fungal partner and an algal and/or cyanobacterial partner.
The fungal partner is on the outside generally which distinguishes lichens from seaweed in which there can be an algal and fungal association but the algae is the main part on the outside on the seaweed frond.
It was not until the 1860s that the true nature of lichens was revealed by the Swiss botanist Simon Schwendener and this concept was not accepted for some time as it contradicted theories at time for example it was thought that the algae were the reproductive cells of the lichen.
The lichenologist Rev. James Crombie disagreed with Schwendener’s theory and referred mockingly to it as ‘..the unnatural union between captive algal damsel & tyrant fungal master’ in 1874…which is quite a nice definition!!

7. Symbiotic relationship i.e. mutual benefit to both Fungus
– provides the alga with structure and shelter from
extremes of temperature, light and moisture.
- forms the majority of the lichen
Autotrophic alga provides heterotrophic fungus with carbohydrates
Cyanobacterial partner (if present) fixes nitrogen also
Allows both to survive in niches and habitats that they would be unable to survive in alone
The partnership benefits both organisms
Algal and cyanobacteria are autotrophic, i.e. they are able to make their own sugars through photosynthesis. Cyanobacteria can also fix nitrogen, i.e. they make it into a form that can be metabolised by the fungi.
Fungi are heterotrophic i.e. they can’t make their own food. Fungi have many nutritional strategies such as parasitism (living off living organisms) or saprophytism (living off dead organisms). Lichenisation is one of these strategies and a common one, almost half of the species in the fungal phylum Ascomycota are lichenised.
Lichens may also be referred to as ‘lichenised fungi’
Lichens because of their unique relationship can survive in places that neither partner could live in alone from Arctic conditions to tropical areas and from below sea level to mountain tops

8. Very different to bryophytes!
Some may look like some thallose liverworts but lichens are:
usually tougher & opaque
a different colour on the underside
They are very different to bryophytes!! Most importantly they’re not plants, algae are photosynthetic but they’re not true plants and fungi are in their own kingdom.
Some species may be confused with thallose liverworts but lichens are usually tougher and opaque, you can’t see through them and they are always a different colour on the underside whereas liverworts are not.

9. Fungal partner
Name given to the lichen applies to fungal partner (mycobiont)
Different fungus in each lichen
98% of lichens in phylum Ascomycota
Remaining 2% in the Basidiomycota and Fungi Imperfecti
~13,500 lichens globally (some estimates up to 18,000)
Because lichens are dual or triple organisms the name given applies to the fungal partner only.
There is a different fungus in each lichen, 98% belong to the phylum Ascomycota and the remaining belong to the Basidiomycota and Fungi Imperfecti
The vast majority of lichens belong to the Ascomycota (98%), but a few are found in the phyla Basidiomycota and Fungi Imperfecti.
The fungal partner makes up the majority of the lichen body (thallus), with the alga being contained in an inner layer (exception: gelatinous lichens).
There is thought to be about 13,500 species globally, some estimates reach 18,000

10. Photobiont partner ~40 genera of photobiont:
~2/3 algae and ~1/3 cyanobacteria
Same photobiont can occur in many lichens
Most common: algae cyanobacterium
There are about 40 genera of photobiont, of which about two thirds are algal genera and the rest are cyanobacterial.
Even though each lichen contains a different fungus, the same photobiont can occur in many different partnerships with different fungi
It’s estimated that world-wide, algae in the Trebouxia genus is found in over 50% of lichen species. About 30% contains Trentepohlia & fewer than 10% contain cyanobacteria, less than 5% contain Nostoc.
Trentepohlia is fairly common in crustose lichens, if you scratch the surface oftentimes you can see the orange colour, due to the carotinoid pigments it contains
Trebouxia genus
Nostoc genus
Trentepohlia genus

11. Growth forms Foliose - Thallus (lichen body) is leaf-like
May have rhizines
Lichens come in various growth forms, which is usually the characteristic you will find very early in identifying keys.
Foilose lichens have thalli (bodies) that are leaf-like and usually have rhizines that attach the lichen to the substratum. These can be an identifying character.
You can see on your handouts (from Dobson, 2005) the arrangement of the fungal and algal partners in the body of the lichen for each growth form….
For example in the foliose lichens you can see the upper cortex with the algal layer beneath it, then the medulla which consists of just fungal hyphae (filaments) and air, and then the lower cortex attached to the substratum by rhizines.

12. Growth forms Fruticose - Shrubby/ branched
Fructicose lichens are branched or shrubby. There is also what are known as filamentous lichens which are hair-like
Fruticose and foliose lichens comprise what are known as macrolichens.

13. Growth forms Leprose ‘Powdery’ No fruiting bodies
Leprose lichens have a powdery form and don’t produce fruiting bodies.
This is a variation on the crustose form…

14. Growth forms Crustose – Thallus lies flat on substratum
– Most common form
The crustose growth form is where the thallus lies flat on the substratum, like a crust. There many variations on this form, for example squamulose lichens are mostly crustose but arise at the edges into scale-like formations.
This is the most common form in Britain and Ireland, with about 80% of lichens are variations on the crustose form and the remaining 20% are macrolichens.
The squiggles and dots you can see on the lichens in the photos are the fruiting bodies and examination of these is essential for identification

15. Sexual Reproduction Ascomycota Ascocarps
Fungal partner – long-lived fruiting bodies release spores
After germination the spore must meet a suitable algal partner before it can develop further
Ascomycota
Ascocarps
- Most common
– spores in ascus
- usually 8 spores
– produced in
perithecia &
apothecia
Basidiomycota
Basidiocarps
- Spores on a
basidium ->
The fruiting bodies arise as a result of sexual reproduction. This only occurs in the fungal partner, the photobiont reproduces asexually.
The fruiting bodies of lichens are very long-lived, especially when compared to the fruiting bodies of fungi that aren’t lichenised. They can release spores throughout the year but in general release rates are higher in winter and spring.
After the fungal spore has been released it must meet a suitable algal partner before it can grow and develop further.
As mentioned earlier the majority of the lichenised fungi are in the phylum Ascomycota and these produce its spores in a structure called an ascus. This usually contains 8 spores, but the number can vary and this can be used as a diagnostic characteristic. The asci (plural of ascus) are contained in one of two possible structures: the perithecium or the apothecium.
Lichenised fungi in the phylum Basidiomycota produce, usually 4, spores on a structure called a basidium but we will talk a bit more about the Ascomycota fruting bodies..

16. Ascocarp fruiting bodies Various forms of apothecia
Hymenium
The apothecium comes in various shapes, sizes and colours but the basic structure is shown here.
The hymenium is the part of the apothecium that contains the spores contained in an ascus and sterile filamentous cells called paraphyses. The number of asci in an apothecium can vary also.
The perithecium is another type of fruiting body, that also contains the asci and paraphyses. It is flask-shaped and spores are released at the top in a opening called an ostiole.

17. Apothecia fruiting bodies
Disc-shaped
Lecanorine – the margin
is the same colour as
the thallus (contains
algal cells)
The apothecia fruiting bodies come in various forms. They may be disc-shaped, and there are two main forms of this:
Lecanorine - where the margin contains algal cells and is the same colour as the thallus, (these look like jam-tarts!) or
Lecideine, where there is no thalline margin
Lecideine – No thalline margin

18. Athonioid – apothecia are poorly defined
Lirellate (elongate)
The fruiting bodies may also be elongate (lirellate), and can sometimes look like ancient writing or scribbles
Arthonioid lichens have apothecia that are poorly defined
Athonioid – apothecia are poorly defined

19. ‘Squash preparations’
Graphina anguina
Graphis scripta
Muriform spores
As you get more experienced you may be able to tell certain species by just examining the fruiting bodies with a hand lens or dissecting microscope (top picture, magnifies up to about x40) but initially, and for some species in general, you will have to make slide preparations in order to see the structure of the hymenium, asci and spores using a compound microscope (bottom picture, magnifies up to x1000).
For example here we have two crustose species that look slightly alike and so for definite identification you need to look at the spores in this case. Graphis scripta has different shaped spores from Graphina anguina. In the case of Graphis scripta the spores are multiseptate, i.e. they have a number of septa (internal walls in a cells) going across (tranversing) the spore cell, whereas Graphina anguina have ‘muriform’ spores, where septa are running up and across the cell (longitudinal and transverse septa).
To do this you must wet up the fruiting body with some water to make it soft, get a razor blade and make very thin incisions across the fruiting body and mount this in a drop of water on a slide. You cover it with a cover-slip, tap it with a pencil and examine the shape of the hymenium and the number of spores per ascus under a compound microscope. You can also add some chemicals, potassium hydroxide and iodine, that cause colour changes in the hymenium or the tip of the ascus, which can turn them blue. You then take the slide off and squash the coverslip with your thumn (covered in tissue to prevent grease getting on the coverslip) in order to release the spores from the asci for further examination.
Multiseptate spores
‘Squash preparations’

20. Lichen reproduction - Asexual
Thallus fragmentation or
More specialised structures:
1) Isidia - minute outgrowths from the thallus that contain both fungal and algal cells and are easily broken off by passing animals and invertebrates and dispersed
Because sexual reproduction is a little risky in that the fungal spore needs to find a photobiont partner or it will die some lichens produce asexual propagules.
Lichens can reproduce asexually when a piece of the thallus (containing both partners) breaks off and finds a suitable substratum.. Specific structures are also formed from fungal and algal cells, these are called isidia and soredia, differing slightly in form.
Isidia are minute outgrowths from the thallus that contain both fungal and algal cells and are easily broken off by passing animals and invertebrates and dispersed
They attach to the substratum elsewhere by fungal hyphae and then growth proceeds.
The shape of the isidia and their position on the thallus can be diagnostic features

21. Lichen reproduction - Asexual
2) Soredia - fine powdery granules also containing both fungal and algal cells and can be spread by water, animals and wind.
Soredia are fine powdery granules also containing both fungal and algal cells and can be spread by water, animals and wind.
Again they attach to the substratum elsewhere by fungal hyphae and then growth proceeds
The position of the soredia on the thallus can be a diagnostic feature

22. Lichen acids Secondary metabolites ~400 known 1-3 in any given lichen
antibiotic properties to defend themselves from bacteria and fungi
allelopathic effects - assist in competing for space with higher plants and bryophytes
prevent against being eaten
~400 known
1-3 in any given lichen
Help with identification
Lichens produce secondary metabolites (unlike primary metabolites they are not essential for growth or survival but have other functions) called lichen acids. These have various functions, they can have antibiotic properties to defend themselves from bacteria and fungi, they can have an adverse chemical effect on other species (allelopathic effect) to help the lichen compete with higher plants and bryophytes. Some of them don’t taste very nice and so can help deter animals from eating them in some cases.
There are about 400 lichen acids known world-wide and 1 to 3 occur in any given lichen in the UK and Ireland.
They have been used in various practises by humans, mentioned earlier, and they can also help with identification

23. Chemical tests Potassium chloride (K) Sodium hypochlorite (C) &
Para-phenylenediamine (Pd)
Cause characteristic colour changes
Drops usually placed on the cortex
for example…..
Chemical spot tests can be performed on lichens to help with their identification. This is where a drop of a certain chemical is placed on the lichen thallus, usually on the cortex (although sometimes on the medulla, the key will tell you which).
Potassium chloride (K), sodium hypochlorite (C), which is just normal household bleach, and para-phenylenediamine (Pd) (not used so much any more as it is thought to be carcinogenic) are all chemicals that cause characteristic colour changes when they react with certain lichen acids.
For example the chemical K causes the cortex of the species Xanthoria parietina to change from orange/yellow to a crimson red

24. Lichen Ecology Climate – wetting/drying cycles
Light availability –shade-tolerant spp.
Quality of environment – air pollution, disturbance,etc
The climate is important, particularly water availability, when dried out lichens cease all metabolic activity. Lichens absorb moisture quite quickly but release it slowly, influenced by wind speed and humidity. Many lichens thrive under these wetting/drying cycles.
Because the photobiont needs light to photosynthesise the light availability is quite important. You can have very high light demanding species for example growing on the canopy of a tree or more shade-tolerant species further down the length, the most shade tolerant nearer the bottom
As we discussed earlier many species are sensitive to pollution and also nutrient-enrichment, and other lichen speces thrive in high-nutrient conditions. Land use is important, nutrient-enrichment can influence the lichen species and grazing can open up an area and allow more light.
Also because some woodland species need a long continuity of canopy cover and no disturbance, these species, if present in a woodland, can indicate the longevity of the woodland. Francis Rose developed a checklist of 30 species that if about 20 are present indicate these conditions. This list has been updated for different areas in Britain and Ireland by Coppins & Coppins.

25. Substratum type – important in identification also Lichens can be:
corticolous (growing on bark)
- saxicolous (growing on rock)
lignicolous (growing on wood)
terricolous (growing on soil)
muscicolous (growing on moss)
lichenicolous (growing on
other lichens)
The condition of the particular substratum is also a factor, for example, acid rocks/bark may support a different range of species than basic rocks/ bark.
The type of substratum is extremely important in determining what lichen species are present.
Lichens can be: corticolous (growing on bark); saxicolous (growing on rock); lignicolous (growing on wood); terricolous (growing on soil); muscicolous (growing on moss) and even lichenicolous (growing on other lichens).
The condition of the particular substratum is also an important factor for example acid bark will support a different suite of species than basic bark would. Also whether the bark is smooth or rough, porous or non-porous, etc will have an influence on the species present.

26. Collecting - Equipment
Hand lens (x 10 & x20)
Spray bottle
Knife
Secateurs (for cutting twigs)
Hammer & chisel
(for collecting lichens on rocks)
Paper packets
The equipment you need for collecting lichens is fairly similar to that you need for collecting bryophytes. The only extra things you may need are secateurs for removing twigs and a hammer and chisel if you’re collecting saxicolous lichens.

27. Lichens by Oliver Gilbert. (2000) by Harper Collins.
Some books on lichens:
Lichens – An Illustrated Guide to the British and Irish Species by Frank S. Dobson (5th edition, 2005). The Richmond Publishing Company Ltd.
Lichens by Oliver Gilbert. (2000) by Harper Collins.
Lichens on Trees (British Plant Life No 3) by Alan Orange (2000) National Museum of Wales.
The Lichen Flora of Britain and Ireland by O.W. Purvis, B.J Coppins, D.L. Hawksworth, P.W. James & D.M. Moore (1992) The British Lichen Society
Some lichen websites:
Lichens of Ireland Project:
LichenIreland Project:
Photographs of Irish lichens:
The British Lichen Society:
Dobson’s guide is best to begin with to get familiar with the forms and some of the terminology but is best used in conjunction with the Purvis book which will have all the details you require.