The Lichens

1
Chapter 7

• The Lichens

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Habitats

• Range
• Bare rock
• Extremes of temperature
• High desiccation
• From sea level to 7000 m on Mt. Everest

3
Habitats

• Bare rock

• Surface of ground

4
Lichens

• On leaves

• On ground

5
Habitats

• Intertidal zone
• Beneath rock surfaces in Namib Desert in South
  Africa
• Require clean air

6
Lichen Anatomy

• What is a lichen?
• It is not an organism in the normal sense
• It is a dual organism, a symbiont
• Symbiosis between fungi and algae
• Mycobiont the fungal symbiont
• Phycobiont the algal component

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Lichen Anatomy

• Mycobiont
• Abosrbs water and minerals from substrate
• Builds complex thallus (undifferentiated body)

8
Lichen Anatomy

• Upper and lower surfaces
• Densely aggregated fungal hyphae
• Round algal cells just beneath upper cortex each
  surrounded by fungal hyphae
• Fungi have captured algae
• Balanced parasitism
• 50 algal food extracted by hyphae

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Lichen Anatomy

• Mycobiont
• Phycobiont
• Mycobiont

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Lichen Taxonomy

• Phycobiont
• Genera
• 25 eukaryotic genera of algae
• 15 prokaryotic cyanobacteria
• 80 lichens contain unicellular
• 10 filamentous green algae
• 10 cyanobacteria

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Lichen Taxonomy

• Phycobiont
• Unicellular alga, Chlorophyta
• Trebouxia sp. (below, L) Nostoc (below. R)

• Trebouxia

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Lichen Taxonomy

• Taxonomy
• Taxonomy based upon the mycobiont
• Names are fungal names
• Foods
• Green algae ? sugar alcohols
• Cyanobacteria ? glucose

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Mycobionts

• Introduction
• 15,000 20,000 lichenized fungi
• 10,000 produce telomorphic fructifications
• The rest produce anamorphic fructifications
• 98 are ascomycetes
• Few lichenized basidiomycetes

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Mycobiont Morphology

• Discolichens
• Fungal fructifications in most lichens are
  apothecia
• Growth Forms
• Crustose lichens closely pressed to or growing
  in rock.

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Mycobiont Morphology

• Crustose lichen
• Note apotheciate ascomata

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Mycobiont Morphology

• Foliose lichens lobed thallus with thread-like
  rhizines, thread-like structures produced by
  lower cortex, attaching thallus to the substrate

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Mycobiont Morphology

• Foliose Lichens
• Parmelia sp.

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Mycobiont Morphology

• Foliose Lichens
• Peltigera neopolydactyla

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Mycobiont Morphology

• Fruticose lichens grow away from their
  substrates and branch repeatedly
• Cladonia bellidiflora is a typical 'British
  Soldier' lichen with bright red apothecial
  ascomata

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Mycobiont Morphology

• Squamulose lichens composed of many small
  upturned scales derived from the cracking and
  fragmentation of a crustose thallus

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Mycobiont Morphology

• Leprose lichens those in which the thallus is a
  loose, powdery material

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Mycobiont Morphology

• Gelationus lichens formed from fungal cortex and
  cyanobacterium, Nostoc
• Note pinkish brown apothecia

23
Sexual Reproduction

• Ascomycetous lichens
• Apothecia, perithecial, pseudothecia
• Some asexual only

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Sexual Reproduction

• Basidiomycetous lichens

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Sexual Reproduction

• Ascus and ascospore production
• Ascus and ascospore production very slow number
  per asci varies
• Due, perhaps, to the slow uptake of energy from
  phycobionts
• Pertusaria sp. 1 spore/ascus
• Acarospora sp. 100 spores/ascus

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Asexual Reproduction

• Pycnidial anamorphs small dots liberating
  conidia

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Asexual Reproduction

• Soredia Somatic propagules
• powdery mass of propagules
• released from ruptures in thallus

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Asexual Reproduction

• Isidia finger-like or branched structure that
  grow up from the thallus

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Taxonomic Groupings

• Orders
• 12 orders of ascomycetes entirely lichenized
• 4 orders with lichenized members

30
Lichen Synthesis

• Process
• Ascospore release from lichen ascoma
• Ascospore and algal cells must be in a
  debilitated condition
• Then agal cell permits fungus to attach to it

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Lichen Synthesis

• Hyphae grow around algal cell and produce
  appressoria
• Appressoria a swelling on a hypha which adheres
  to the surface of the algal cell
• Algal physiology altered
• cell membrane becomes leaky,
• loses large quantities of soluble carbohydates

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Lichen Synthesis

• Note fungal hyphae
• Note appressorium
• Note algal cell

33
Lichen Growth

• Growth rates
• Growth very slow since thallus dried out most
  of the year
• Some grow fast where waters abundant
• Some grow very slowly where waters scarce
• 1-4mm/year is respectable rate of growth

34
Lichen Growth

• Oldest lichen colonies estimated to be 4,500
  years old
• Oldest flowering plants bristlecone pine in
  California, 4,500 years old

35
Lichen Growth

• Lichen growth on a grave marker
• Year of grave marker is the start point
• Diameter of colony/years annual growth rate