Lichens in Gardens
 
Many of us are well aware of the wildlife in our gardens, whether it’s lounging foxes, singing wrens or busy bees. But how many of us stop to look at lichens? Fascinating, diverse and often beautiful, lichens are well worth looking for. You may be surprised by the range of species when you search for them.
 
 
 
Observing lichens gives garden wildlife watching an extra dimension. Unlike most garden plants and animals they can be best seen in the winter when leaves are off the trees and the world is wet. Once you begin to find them it is easy to become hooked! Why not have a look and see what you find in your area?
 
References
 
1.  Laundon, J.R. (2012). Lichens invade the City of London. The London Naturalist 91: 53-68.
2.  Powell, M. Beale, J. and Shipway, P. (2017). Bull. Brit. Lichen Soc. 121: 45-52.
3.  Allen, A. & Hilton, B. (2011). Lichen diversity in gardens. Bull. Brit. Lichen Soc. 108: 11-32.
 
 
Books and websites
 
 
Field Studies Council fold-out guides: Urban Lichens 1 lichens on wood  Urban Lichens 2 lichens on stone and soil Good for getting started, but bear in mind they only cover a selection of species.
 
Frank Dobson (2018) Lichens: an Illustrated Guide to the British and Irish Species (7th edition) by  Richmond Publishing, Slough. For those who are looking at lichens in more depth.
 
Field Studies Council fold-out chartKey to Lichens on Twigs by Pat Wolseley, Peter James & Diccon Alexander (2003). FSC
 
Field Studies CouncilA Field Key to Common Churchyard Lichens by Frank Dobson (2006). 2nd edition. 38pp.
 
The British Lichen Society website 
 
Lichens section of Fungi of Great Britain and Ireland
 
Key to common lichens on trees in England Webpage here
 
Lichens of Wales website Useful resources to explore
 
 
Page written by Jo Beale, reviewed by Ceri Leigh and compiled by Steve Head
What is a lichen? 
 
Lichens are symbiotic partnerships between a fungus and a species of algae or cyanobacteria (once called blue-green algae), though they can be more complex with more than two partners which may include yeasts. One key point to remember is that the lichen is always named after the fungal partner. The algal partner may be incorporated into many different lichens, but the fungal component is different each time. In some cases, the shape and structure of one lichen species may look very different depending on the type of algal partner.
 
The body of the lichen is called a thallus. The algal cells typically form a layer just below the upper surface (cortex) where they receive light for photosynthesis in which which food is produced from sunlight, air and water. The fungus partner benefits from some of this food, while the alga receives shelter, water and nutrients from the fungus.
 
In some lichens the upper and lower cortex layers are different, and some produce root-like rizines which only anchor the lichen rather than collecting water.
 
Types of lichen:
 
There are four key types or body forms of garden lichen which help categorise them:
 
•    Crustose lichens
      Crust-like and would be difficult to peel from the substrate without damage.
 
•    Foliose lichens
      Leafy, with a clear upper and lower surface which could be peeled from the substrate. Some crustose lichens
      have lobes around the edges which look foliose
 
•    Fruticose lichens
      Bushy, attached by one point to the substrate. A few foliose species also resemble fruticose species — in
      particular Evernia prunastri, though this species is notable for its white, algae free underside.
 
•    Leprose lichens
      Powdery, often in crevices of trees and rocks. They are a simply structured mix of fungal and algal cells lacking
      an outer ‘skin’ or cortex.
 
Lichen ecology
 
Lichens occupy many different niches but usually require plenty of sunlight and some moisture. You will usually see more lichens in sunny positions than in shaded areas. Some avoid exposure and some, such as Xanthoria, favour it. Lichens may grow on stone or concrete, tree bark, cut wood, soil, metal and other substrates. A few like the base of trees in parks where dogs urinate, while others will only grow above that zone! Lichens provide material for birds nests — long-tailed tits for example, and food for the larvae of some moths such as the footman or bagworm moths. The larvae of bagworm moths such as Psyche casta carry around protective cases covered with lichen or other vegetation fragments, very like caddisfly larvae do in water. Lichens also provide shelter or food for invertebrates such as springtails, while slugs and snails graze on lichens. They also contribute to early stages of soil formation, a process which is later taken over by mosses and other plants.
 
Lichens and pollution
 
Lichens suffer if there is too much sulphur dioxide in the air. The east of England almost became a lichen desert during the era of coal, before the Clean Air Act of 1956. One or two sulphur tolerant species predominated, in particular Lecanora conizaeoides, which is now uncommon. A study by Laundon1 notes that there were no lichens recorded in the City of London in 1954, whereas 42 species were recorded between 1973 to 2011. Many species have recolonised in the decades since then, although air pollution from nitrogen dioxide and ammonia are still a serious problem for many species. This limits the number of lichen species able to gain a foothold in many urban and agricultural areas across the UK. Today nitrogen tolerant species such as Xanthoria parietina and Physcia adscendens are very common, at least in urban areas and near farmland. The lichen flora even changes the nearer you get to the road due to pollutants from vehicle exhausts.
 
Sometimes younger trees in cities have a richer lichen flora than old trees, which seems counter-intuitive. Lichenologist Mark Powell explains this as ‘toxic legacy’2 (Powell, Beale & Shipway 2017), as the bark of old trees does not change or replenish quickly, holding on to some of the acidity and pollutants that used to be in the air. The situation can be rather different away from the east and south-east of England and urban areas.
 
Which species can we see in our gardens?
 
The lichens you see in your garden will have arrived naturally from spores or fragments via animals, wind and rain, although some may come in on the bark of introduced trees and shrubs. In a typical London park there could be a wide range of lichens, mainly crustose and foliose species. For example, over ninety lichens have been recorded in Greenwich Park in recent years — a far cry from the days of high levels of atmospheric sulphur pollution. Parks in western areas that avoided the worst historic air pollution may have more species and many of these species are likely to occur in nearby gardens. One study3 looked at lichens in 45 gardens and found an impressive 310 species. In their study the south-west, with cleaner air and plentiful rainfall, scored highest for lichen diversity, followed by the Midlands. Larger gardens had more niches on average and so generally produced more lichen records, as might be expected.
 
Lichens on stone
 
Any exposed concrete or stone, especially old walls or sculptures, may be colonised by crustose lichens if they are not cleaned. Have a look on paths for two of the ‘chewing gum’ lichens: Lecanora muralis and Aspicilia contorta. Lecanora muralis is beautiful when not worn down, with orange-beige fruits and a rosette shaped, pale green thallus, while Aspicilia contorta is whitish grey and close-up appears cracked like parched earth. A lichen with dark brown, ‘jam tart’ fruits and when seen under a hand lens, has a whitish fringe around its perimeter resembling cotton wool, is likely to be Lecanora campestris.
 
 
Section through a lichen thallus
 
Lecanora conizaeoides a pollution resistant species now uncommon
Chewing gum lichen Lecanora muralis       Aspicilia contorta                                  Lecanora campestris
 
Also on twigs and branches you may see camouflaged olive-brown leafy lichens such as Melanelixia subaurifera or on larger branches the big, grey rosettes of Parmelia sulcata, with its fine, pale lines across the leafy lobes. Punctelia species are similar, though they appear a bit more greenish-yellow and are ‘punctuated’ with tiny pale dots on the lobes.
 
 
 
 
 
 
Lichens on trees
 
A good place to look in a garden is on the small branches of trees that get plenty of light. Fruit trees such as apple are often productive, along with mulberry, rowan and hawthorn. Dead branches may have more lichens as there are no leaves to block out the light.
 
On the smooth bark of deciduous trees look for the small black asterisks of the crustose Arthonia radiata, or the black ‘wine gum’ dots on a pale greenish-white thallus of Lecidella elaeochroma — a very common species.
 
                          Arthonia radiata                                                Lecidella elaeochroma
 
 
A bushy green lichen on branches could be a fruiticose Ramalina species or it could prove to be the foliose species Evernia prunastri which has a green upper surface with a tell-tale white underside.
                 Ramalina farinacea                                                           Evernia prunastri 
 
 
Large areas of yellow, leafy lichens with ‘jam tart’ fruits are likely to be Xanthoria parietina which is a very common foliose lichen in urban areas and gardens, growing on a range of surfaces, especially twigs and branches. Check to see if any areas have become blackened as if burnt — this may be Xanthoriicola physciae — a lichenicolous fungus that attacks this lichen.
                     Xanthoria parietina                      Fungus Xanthoriicola physciae attacking Xanthoria parietina.
 
 
Xanthoria parietina is often in a lichen community together with the pale grey Physcia adscendens and Physcia tenella. If the Physcia has pale ‘hoodies’ it is Physcia adscendens, but if the lobes are turned up at the tip showing soredia (vegetative propagules looking like tiny grains of green sand) it will be Physcia tenella. Look closely for any discoloured areas with pinkish lumps, as these may be lichenicolous fungi. Tiny pale orange-pink bulbils may be Marchandiobasidium aurantiacum, but other pink species occur on Physcia.
Above: Physcia adscendens (left) and Physcia tenella (right)
 
Below: fungus Marchandiobasidium aurantiacum 
          Melanelixia subaurifera                       Parmelia sulcata                          Punctelia subrudecta
 
Tree trunks and stumps may host the small, thin, finger-like projections of Cladonia coniocraea and in the crevices powdery, mint green Lepraria may occur, such as Lepraria incana. Other cladonias, with goblet-like podetia (stalks with fruiting bodies) may occur on shingle or green roofs. A mass of uniform yellow, consisting of many small, finely sculpted lobes on bark may belong to Candelaria concolor — large areas of bark can sometimes be covered by this lichen
 
Above: (left) Cladonia coniocraea  (right) Lepraria incana.
 
Below: Candelaria concolor 
Lichens in Gardens
 
Many of us are well aware of the wildlife in our gardens, whether it’s lounging foxes, singing wrens or busy bees. But how many of us stop to look at lichens? Fascinating, diverse and often beautiful, lichens are well worth looking for. You may be surprised by the range of species when you search for them.
 
 
 
Lichens in Gardens
 
Many of us are well aware of the wildlife in our gardens, whether it’s lounging foxes, singing wrens or busy bees. But how many of us stop to look at lichens? Fascinating, diverse and often beautiful, lichens are well worth looking for. You may be surprised by the range of species when you search for them.
 
 
 
Lichens in Gardens
 
Many of us are well aware of the wildlife in our gardens, whether it’s lounging foxes, singing wrens or busy bees. But how many of us stop to look at lichens? Fascinating, diverse and often beautiful, lichens are well worth looking for. You may be surprised by the range of species when you search for them.
 
 
 
Lichens in Gardens
 
Many of us are well aware of the wildlife in our gardens, whether it’s lounging foxes, singing wrens or busy bees. But how many of us stop to look at lichens? Fascinating, diverse and often beautiful, lichens are well worth looking for. You may be surprised by the range of species when you search for them.
 
What is a lichen? 
 
Lichens are symbiotic partnerships between a fungus and a species of algae or cyanobacteria (once called blue-green algae), though they can be more complex with more than two partners which may include yeasts. One key point to remember is that the lichen is always named after the fungal partner. The algal partner may be incorporated into many different lichens, but the fungal component is different each time. In some cases, the shape and structure of one lichen species may look very different depending on the type of algal partner.
 
The body of the lichen is called a thallus. The algal cells typically form a layer just below the upper surface (cortex) where they receive light for photosynthesis in which which food is produced from sunlight, air and water. The fungus partner benefits from some of this food, while the alga receives shelter, water and nutrients from the fungus.
 
In some lichens the upper and lower cortex layers are different, and some produce root-like rizines which only anchor the lichen rather than collecting water.
 
 
 
 
Types of lichen:
 
There are four key types or body forms of garden lichen which help categorise them:
 
•    Crustose lichens
      Crust-like and would be difficult to peel from the substrate without damage.
 
•    Foliose lichens
      Leafy, with a clear upper and lower surface which could be peeled from the
      substrate. Some crustose lichens have lobes around the edges which look  
      foliose
 
•    Fruticose lichens
      Bushy, attached by one point to the substrate. A few foliose species also
      resemble fruticose species — inparticular Evernia prunastri, though this 
      species is notable for its white, algae free underside.
 
•    Leprose lichens
      Powdery, often in crevices of trees and rocks. They are a simply structured
      mix of fungal and algal cells lacking an outer ‘skin’ or cortex.
 
Lichen ecology
 
Lichens occupy many different niches but usually require plenty of sunlight and some moisture. You will usually see more lichens in sunny positions than in shaded areas. Some avoid exposure and some, such as Xanthoria, favour it. Lichens may grow on stone or concrete, tree bark, cut wood, soil, metal and other substrates. A few like the base of trees in parks where dogs urinate, while others will only grow above that zone! Lichens provide material for birds nests — long-tailed tits for example, and food for the larvae of some moths such as the footman or bagworm moths. The larvae of bagworm moths such as Psyche casta carry around protective cases covered with lichen or other vegetation fragments, very like caddisfly larvae do in water. Lichens also provide shelter or food for invertebrates such as springtails, while slugs and snails graze on lichens. They also contribute to early stages of soil formation, a process which is later taken over by mosses and other plants.
 
Lichens and pollution
 
Lichens suffer if there is too much sulphur dioxide in the air. The east of England almost became a lichen desert during the era of coal, before the Clean Air Act of 1956. One or two sulphur tolerant species predominated, in particular Lecanora conizaeoides, which is now uncommon. A study by Laundon1 notes that there were no lichens recorded in the City of London in 1954, whereas 42 species were recorded between 1973 to 2011. Many species have recolonised in the decades since then, although air pollution from nitrogen dioxide and ammonia are still a serious problem for many species. This limits the number of lichen species able to gain a foothold in many urban and agricultural areas across the UK. Today nitrogen tolerant species such as Xanthoria parietina and Physcia adscendens are very common, at least in urban areas and near farmland. The lichen flora even changes the nearer you get to the road due to pollutants from vehicle exhausts.
 
Sometimes younger trees in cities have a richer lichen flora than old trees, which seems counter-intuitive. Lichenologist Mark Powell explains this as ‘toxic legacy’2 , as the bark of old trees does not change or replenish quickly, holding on to some of the acidity and pollutants that used to be in the air. The situation can be rather different away from the east and south-east of England and urban areas.
 
 
Lecanora conizaeoides a pollution resistant species now uncommon
Which species can we see in our gardens?
 
The lichens you see in your garden will have arrived naturally from spores or fragments via animals, wind and rain, although some may come in on the bark of introduced trees and shrubs. In a typical London park there could be a wide range of lichens, mainly crustose and foliose species. For example, over ninety lichens have been recorded in Greenwich Park in recent years — a far cry from the days of high levels of atmospheric sulphur pollution. Parks in western areas that avoided the worst historic air pollution may have more species and many of these species are likely to occur in nearby gardens. One study3 looked at lichens in 45 gardens and found an impressive 310 species. In their study the south-west, with cleaner air and plentiful rainfall, scored highest for lichen diversity, followed by the Midlands. Larger gardens had more niches on average and so generally produced more lichen records, as might be expected.
 
Lichens on stone
 
Any exposed concrete or stone, especially old walls or sculptures, may be colonised by crustose lichens if they are not cleaned. Have a look on paths for two of the ‘chewing gum’ lichens: Lecanora muralis and Aspicilia contorta. Lecanora muralis is beautiful when not worn down, with orange-beige fruits and a rosette shaped, pale green thallus, while Aspicilia contorta is whitish grey and close-up appears cracked like parched earth. A lichen with dark brown, ‘jam tart’ fruits and when seen under a hand lens, has a whitish fringe around its perimeter resembling cotton wool, is likely to be Lecanora campestris.
 
 
Above: (left) Chewing gum lichen Lecanora muralis       (right) Aspicilia contorta                                 
Below: Lecanora campestris
Lichens on trees
 
A good place to look in a garden is on the small branches of trees that get plenty of light. Fruit trees such as apple are often productive, along with mulberry, rowan and hawthorn. Dead branches may have more lichens as there are no leaves to block out the light.
 
On the smooth bark of deciduous trees look for the small black asterisks of the crustose Arthonia radiata, or the black ‘wine gum’ dots on a pale greenish-white thallus of Lecidella elaeochroma — a very common species.
 
                     Arthonia radiata                              Lecidella elaeochroma
 
A bushy green lichen on branches could be a fruiticose Ramalina species or it could prove to be the foliose species Evernia prunastri which has a green upper surface with a tell-tale white underside.
              Ramalina farinacea                               Evernia prunastri 
 
Large areas of yellow, leafy lichens with ‘jam tart’ fruits are likely to be Xanthoria parietina which is a very common foliose lichen in urban areas and gardens, growing on a range of surfaces, especially twigs and branches. Check to see if any areas have become blackened as if burnt — this may be Xanthoriicola physciae — a lichenicolous fungus that attacks this lichen.
               Xanthoria parietina                      Fungus Xanthoriicola physciae
                                                              attacking Xanthoria parietina.
 
Xanthoria parietina is often in a lichen community together with the pale grey Physcia adscendens and Physcia tenella. If the Physcia has pale ‘hoodies’ it is Physcia adscendens, but if the lobes are turned up at the tip showing soredia (vegetative propagules looking like tiny grains of green sand) it will be Physcia tenella. Look closely for any discoloured areas with pinkish lumps, as these may be lichenicolous fungi. Tiny pale orange-pink bulbils may be Marchandiobasidium aurantiacum, but other pink species occur on Physcia.
Above: Physcia adscendens (left) and Physcia tenella (right)
 
Below: fungus Marchandiobasidium aurantiacum 
 
Also on twigs and branches you may see camouflaged olive-brown leafy lichens such as Melanelixia subaurifera or on larger branches the big, grey rosettes of Parmelia sulcata, with its fine, pale lines across the leafy lobes. Punctelia species are similar, though they appear a bit more greenish-yellow and are ‘punctuated’ with tiny pale dots on the lobes.
 
 
 
 
 
 
          
 
Tree trunks and stumps may host the small, thin, finger-like projections of Cladonia coniocraea and in the crevices powdery, mint green Lepraria may occur, such as Lepraria incana. Other cladonias, with goblet-like podetia (stalks with fruiting bodies) may occur on shingle or green roofs. A mass of uniform yellow, consisting of many small, finely sculpted lobes on bark may belong to Candelaria concolor — large areas of bark can sometimes be covered by this lichen
 
Above: (left) Melanelixia subaurifera  (right) Parmelia sulcata                
 
Below: Punctelia subrudecta
Above: (left) Cladonia coniocraea  (right) Lepraria incana.
 
Below: Candelaria concolor 
Observing lichens gives garden wildlife watching an extra dimension. Unlike most garden plants and animals they can be best seen in the winter when leaves are off the trees and the world is wet. Once you begin to find them it is easy to become hooked! Why not have a look and see what you find in your area?
 
References
 
1.  Laundon, J.R. (2012). Lichens invade the City of London. The London Naturalist 91: 53-68.
2.  Powell, M. Beale, J. and Shipway, P. (2017). Bull. Brit. Lichen Soc. 121: 45-52.
3.  Allen, A. & Hilton, B. (2011). Lichen diversity in gardens. Bull. Brit. Lichen Soc. 108: 11-32.
 
 
Books and websites
 
 
Field Studies Council fold-out guides: Urban Lichens 1 lichens on wood  Urban Lichens 2 lichens on stone and soil Good for getting started, but bear in mind they only cover a selection of species.
 
Frank Dobson (2018) Lichens: an Illustrated Guide to the British and Irish Species (7th edition) by  Richmond Publishing, Slough. For those who are looking at lichens in more depth.
 
Field Studies Council fold-out chartKey to Lichens on Twigs by Pat Wolseley, Peter James & Diccon Alexander (2003). FSC
 
Field Studies CouncilA Field Key to Common Churchyard Lichens by Frank Dobson (2006). 2nd edition. 38pp.
 
The British Lichen Society website 
 
Lichens section of Fungi of Great Britain and Ireland
 
Key to common lichens on trees in England Webpage here
 
Lichens of Wales website Useful resources to explore
 
 
Page written by Jo Beale, reviewed by Ceri Leigh and compiled by Steve Head
           Garden Wildplants
        Garden Wildplants