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Lichens. Pl P 421/521 General Mycology. 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. Mycobionts.

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Pl P 421/521

General Mycology

  • 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
  • >13,500 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


From Blackwell et al. 2006. Mycologia 98: 834

Lichenized ascomycetes belong to class Lecanoromycetes

class lecanoromycetes
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

  • 24 genera of green algae are lichenized; Trebouxia in >75% of known lichens
  • ~10% of lichens have a cyanobacterium; most belong to Nostoc
  • Photobiont/mycobiont interface is wall-to-wall or intracellular haustoria
lichen thalli
Lichen thalli
  • Discrete
  • Unique form that bears no resemblance to non-lichenized alga or fungus
  • Slow-growing
    • most grow <1mm/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
types of lichens


Types of lichens
  • Non-stratified
    • Photobiont cells evenly distributed throughout thallus


types of lichens9
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
  • 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
fruiting bodies
Fruiting bodies

Photos by Sylvia/Stephen Sharnoff



Soredia in soralium


growth forms
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
foliose lichens
Foliose lichens

Peltigera elizabethae

foliose lichens16
Foliose lichens
  • Lobaria pulmonaria--Lungwort

foliose lichens17
Foliose lichens



organs of attachment
Organs of attachment



fruticose lichens
Fruticose lichens

Alectoria sarmentosa


fruticose lichens20
Fruticose lichens

Letharia vulpina

squamulose lichens
Squamulose lichens



crustose lichens
Crustose lichens


secondary metabolites
Secondary metabolites
  • Comprise 40% or more of the thallus dry weight
  • > 400 secondary metabolites identified
  • Metabolites are unique to the association, not produced by either partner when grown alone
  • May provide defenses against other organisms
how are lichens used
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)
  • Medicines—antiviral and antibacterial
    • Up to 50% of all lichens believed to have antibiotic properties
  • 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
lichens as components of soil crusts
Lichens as components of soil crusts

Images from

lichens on the internet
Lichens on the internet

Lichens of North America

The Microbial World—Lichens

Lichen Land

Welcome to the World of Lichenology

Soil Crusts