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Lichens

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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Lichens

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  1. Lichens Pl P 421/521 General Mycology

  2. 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

  3. Mycobionts • >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 http://www.kki.pl/zenit/grzyby_spyt

  4. From Blackwell et al. 2006. Mycologia 98: 834 Lichenized ascomycetes belong to class Lecanoromycetes

  5. 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

  6. Photobionts • 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

  7. 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

  8. Leptogium Types of lichens • Non-stratified • Photobiont cells evenly distributed throughout thallus Collema

  9. 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

  10. 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

  11. Fruiting bodies Photos by Sylvia/Stephen Sharnoff http://www.lichen.com/index.html

  12. Cephalodia

  13. Diaspores cortex Soredia in soralium Isidia

  14. 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

  15. Foliose lichens Peltigera elizabethae

  16. Foliose lichens • Lobaria pulmonaria--Lungwort http://www.mcelroy.ca/bushlog/images/10a-4329.jpg

  17. Foliose lichens Umbilicaria Xanthoparmelia

  18. Organs of attachment rhizines umbilicus

  19. Fruticose lichens Alectoria sarmentosa http://www.lichen.coml

  20. Fruticose lichens Letharia vulpina

  21. Squamulose lichens podetia Cladonia

  22. Crustose lichens Rhizocarpon

  23. 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

  24. 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

  25. 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

  26. Lichens as components of soil crusts Images from www.soilcrust.org

  27. Lichens on the internet Lichens of North America http://www.lichen.com/index.html The Microbial World—Lichens 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

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