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Lichens
Why study lichens?• Important part of Ireland’s biodiversity
with ~1,165 species• West of Ireland very important
Photo: Maria Long
• Pollution indicators• Disappearance of
lichens led to black (melanistic) form of peppered moth
• Hawksworth & Rose scale (1970)• 0-10 for acid and
basic bark
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/E/Evolution.html
• Used for dyeing e.g. crottle
• Used in medicine
• Used in perfumes & pot pourri
• Lichens provide food and/or shelter for animals http://www.irishlichens.ie/pages-lichen/l-18.html
• Under-recorded• Year-round activity
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
• 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
• Very different to bryophytes! – Some may look like
some thallose liverworts but lichens are:• usually tougher &
opaque• a different colour
on the underside
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)
Photobiont partner• ~40 genera of photobiont:
~2/3 algae and ~1/3 cyanobacteria• Same photobiont can occur in many lichensMost common:
algae cyanobacterium
Trebouxia genus
Trentepohlia genus
Nostoc genus
Growth forms• Foliose - Thallus (lichen
body) is leaf-like- May have rhizines
http://1.bp.blogspot.com/-AcO6nxzHY1U/TXfbl1TopxI
Growth forms• Fruticose- Shrubby/ branched
Growth forms• Leprose- ‘Powdery’ - No fruiting bodies
Growth forms• Crustose – Thallus lies flat
on substratum– Most common
form
Sexual Reproduction• Fungal partner – long-lived fruiting bodies release
spores• After germination the spore must meet a suitable
algal partner before it can develop further
AscomycotaAscocarps - Most common– spores in ascus - usually 8 spores – produced in perithecia & apothecia
BasidiomycotaBasidiocarps- Spores on a basidium ->
Ascocarp fruiting bodies
Various forms of apotheciaHymenium
Apothecia fruiting bodies Disc-
shaped Lecanorine – the margin is the same colour as the thallus (contains algal cells)
Lecideine – No thalline margin
http://www.fungalpunknature.co.uk/Others/MossLichGall/LecanoraChlarotera.jpg
Lirellate (elongate)
Athonioid – apothecia are poorly defined
‘Squash preparations’Multiseptate spores
Muriform spores
Graphis scriptaGraphina anguina
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
http://gis.nacse.org/lichenair/
Lichen reproduction - Asexual
2) Soredia - fine powdery granules also containing both fungal and algal cells and can be spread by water, animals and wind.
http://www.kollathdesign.com/images/gallery/soredia.jpg
Lichen acids
• Secondary metabolites– 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
Chemical tests
• Potassium chloride (K)• Sodium hypochlorite (C) & • Para-phenylenediamine (Pd)• Cause characteristic colour changes• Drops usually placed on the cortex
for example…..
Lichen Ecology• Climate – wetting/drying cycles• Light availability –shade-tolerant spp.• Quality of environment – air pollution,
disturbance,etc
Substratum type – important in identification alsoLichens 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.
Collecting - Equipment
• Hand lens (x 10 & x20)• Spray bottle• Knife• Secateurs (for cutting twigs)• Hammer & chisel (for collecting lichens on rocks)• Paper packets
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: http://www.lichens.ie/
• LichenIreland Project: http://www.habitas.org.uk/lichenireland/
• Photographs of Irish lichens: http://www.irishlichens.ie/
• The British Lichen Society: http://www.thebls.org.uk/