Lichens

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Lichens

• Pl P 421/521
• General Mycology

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Definitions

• Lichen
• An association between a fungus and a
  photosynthetic partner
• Mycobiont
• The fungal partner in a lichen
• Photobiont
• The photosynthetic partner in a lichen either a
  green alga or cyanobacterium

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Mycobionts

• gt13,500 species of lichens recognized
• 20 of all known fungal taxa
• 50 of ascomycetes
• Most are inoperculate discomycetes
• Relatively few basidiomycete mycobionts, notably
  Omphalina and Multiclavula

http//www.kki.pl/zenit/grzyby_spyt
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From Blackwell et al. 2006. Mycologia 98 834
Lichenized ascomycetes belong to class
Lecanoromycetes
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Class Lecanoromycetes

• Largest class of Fungi
• Includes 90 of all lichen-forming ascomycetes
• Most form apothecia
• Most have asci with two walls visible with light
  microscopy
• Most produce a wide variety of secondary
  metabolites of biological and ecological
  importance

Image from Miadlikowska et al. 2006. Mycologia
98 1096
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Photobionts

• 24 genera of green algae are lichenized
  Trebouxia in gt75 of known lichens
• 10 of lichens have a cyanobacterium most
  belong to Nostoc
• Photobiont/mycobiont interface is wall-to-wall or
  intracellular haustoria

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Lichen thalli

• Discrete
• Unique form that bears no resemblance to
  non-lichenized alga or fungus
• Slow-growing
• most grow lt1mm/year, maximum of 4 cm/year
• Growth favored by high humidity, cool temps and
  low light
• Long-lived
• Reach maturity at 4-8 years
• Alpine-arctic lichens may be 1000-4500 years old
• Longevity attributable to ability to withstand
  drought periods of several months
• Able to absorb up 300 of its weight in water
  when available

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Types of lichens
Leptogium

• Non-stratified
• Photobiont cells evenly distributed throughout
  thallus

Collema
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Types of lichens

• Stratified
• Differentiated into cortex (upper only, or upper
  and lower) and medulla
• Photobiont cells form a discrete layer just under
  upper cortex

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Reproduction

• Conidia
• Meiospores (ascospores basidiospores)
• Diaspores vegetative propagules
• Cephalodia
• Gall-like swellings containing cyanobacteria on
  or in thallus of lichen with algal photobiont
  primary function is nitrogen fixation, may also
  be propagule
• Isidia
• Small, cortex-covered protuberance containing
  fungal and algal cells
• Soredia
• A few algal cells surrounded by fungal hyphae
  formed in small, pustule-like breaks in cortex
  called soralia

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Fruiting bodies
Photos by Sylvia/Stephen Sharnoff http//www.liche
n.com/index.html
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Cephalodia
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Diaspores
cortex
Soredia in soralium
Isidia
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Growth forms

• Dust/leprose
• Lack both upper and lower cortex, medulla
  attached directly to substrate
• Crustose
• Lacking a lower cortex, attached to soil, rock or
  bark by hyphae of the medulla
• Squamulose
• Lacking lower cortex, composed of scale-like
  segments, often giving rise to erect podetia
• Foliose
• Flattened, leaf-like thallus with an upper and
  lower cortex lower cortex often with rhizines
• Fruticose
• Strap-like or threadlike thallus, often attached
  to substrate by holdfast

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Foliose lichens
Peltigera elizabethae
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Foliose lichens
http//www.mcelroy.ca/bushlog/images/10a-4329.jpg

• Lobaria pulmonaria--Lungwort

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Foliose lichens
Xanthoparmelia
Umbilicaria
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Organs of attachment
rhizines
umbilicus
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Fruticose lichens
Alectoria sarmentosa
http//www.lichen.coml
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Fruticose lichens
Letharia vulpina
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Squamulose lichens
podetia
Cladonia
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Crustose lichens
Rhizocarpon
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Secondary metabolites

• Comprise 40 or more of the thallus dry weight
• gt 400 secondary metabolites identified
• Metabolites are unique to the association, not
  produced by either partner when grown alone
• May provide defenses against other organisms

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How are lichens used?

• Nesting/bedding, food source for animals
• Source of dyes
• litmus paper
• Woolens such as Harris tweed
• Essential oils for perfumes, soaps
• Oakmoss (Evernia)
• Medicinesantiviral and antibacterial
• Up to 50 of all lichens believed to have
  antibiotic properties

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Distribution

• Worldwide, in some of the most extreme
  environments, from the Arctic to Antarctic,
  deserts to tropics
• Occur on soil, plants, animals, on or in rock,
  and on man-made structures
• Mainly in rural areas rather than cities
• Lichens are intolerant of atmospheric pollution,
  particularly sulphur dioxide

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Lichens as components of soil crusts
Images from www.soilcrust.org
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Lichens on the internet

• Lichens of North America
• http//www.lichen.com/index.html
• The Microbial WorldLichens
• http//helios.bto.ed.ac.uk/bto/microbes/lichen.htm
  
• Lichen Land
• http//mgd.nacse.org/hyperSQL/lichenland/
• Welcome to the World of Lichenology
• http//www.botany.hawaii.edu/cpsu/lichen1.html
• Soil Crusts
• http//www.soilcrust.org