The Lichens Where do lichens belong in the
The Lichens
Where do lichens belong in the classification of living organisms? * Lichens are dual organisms, so they are difficult to place in a classification * They represent symbiotic (mutualistic) relationships between fungi and green algae, fungi and cyanobacteria, or fungi and both * The fungus is the dominant physical component of the lichen thallus, and lichens are usually classified with the fungi * Nevertheless, the association appears to have originated through fungi parasitizing algae and/or cyanobacteria
The two components can be separated and grown independently Isolation of fungus (Richardson) Fungus and alga in culture (Richardson)
Functional Aspects of the Symbiosis * What does the fungus gain from the alga? Richardson’s summary of movement of carbohydrate from Trebouxia to fungus Where cyanobacteria are present, the fungus also acquires nitrogen * What does the alga gain from the fungus? A substrate and stable environment Mineral nutrients ? ?
SEMs of reconstitution of a lichen (Cladonia cristatella British Soldier) (from Raven) (a) Trebouxia cell surrounded by fungal hyphae (b) Penetration by haustorium (see arrow) (a) (b) (c) Mixed components developing into mature lichen
Identity of the mycobiont and phycobiont * Each of approximately 20, 000 known species of lichen is assumed to have its own unique mycobiont * Most mycobionts are Ascomycetes, although about twenty lichenized Basidiomycetes are known * In 90% of the lichens, the phycobiont is a green alga of the genus Trebouxia, Pseudotrebouxia or Trentepohlia * Where cyanobacteria are involved, they are Nostoc or Anaboena * Lichen-forming fungi rarely grow alone in nature, while the algal components frequently do * Algae and cyanobacteria grow faster when NOT part of a lichen
Main thallus forms in lichens Crustose Squamulose, with fruticose podetia Foliose Fruticose Less commonly, lichens are sorediate or gelatinous
Thallus Structure Upper cortex Crosssection of thallus of Parmelia (foliose lichen) Algal layer Medulla Lower cortex
Structural features of lichens (Scagel) A. Thallus with black cephalodia A. Isidia on upper surface B. Closeup of cephalodia C. Vertical section through cephalodium B. Isidia in section Isidia (coral-like outgrowths) of Lobaria Cephalodia (warty epiphytic lichens) on Peltigera
More structural features of lichens cyphellae & pseudocyphellae A. Cyphella (cupshaped depression of non-gelatinized hyphae) in lower cortex of Sticta B. Pseudocyphella (small pore forming white dot) in lower cortex of Sticta
Asexual reproduction in lichens * Fragmentation of thallus when dry and brittle * Detachment of isidia * Loose dusty masses of soredia * Pycnidia A. Soredia bursting through thallus of Lobaria B. External view of sorediate mass Pycnidium of Lecanora
Sexual Reproduction in Lichens * Only the fungal partner undergoes sexual reproduction * In the ascomycetous (i. e. most) lichens, ascospores are formed in sacs called asci, mixed with paraphyses to form a hymenium. * Asci can be arranged on an open or convex or concave disk, when it is called an APOTHECIUM, or in an immersed, urnshaped PERITHECIUM. Apothecium (Scagel) Perithecium (Scagel)
Podetia A podetium is a specialized structure that raises the apothecia above the rest of the thallus Cladonia cristatella (British Soldiers) Cladonia deformis Cladonia verticillata
Growth of Lichens * Growth is very slow * 0. 1 - 10 mm in crustose lichens * 2 -4 cm in some fruticose lichens * Some crustose lichens have been estimated to be over 4, 000 years old
Lichens in the food chain * Species of Cladonia and Stereocaulon paschale form a major winter food source for subspecies and varieties of Rangifer tarandus (e. g. caribou in N. America and Reindeer in Europe) * Other deer, such as Roosevelt elk and black-tailed deer of Western Canada, and the musk-oxen of the high arctic, graze on lichens in the winter * A number of mites and insect larvae feed on lichens * A number of snails and periwinkles also feed on lichens
Other uses of lichens by animals * Birds’ nest building material and camouflage Nest of long-tailed titmouse made of lichen in the UK (Richardson) * Insect camouflage * Mimicry Lichencovered lacewing larva Scalloped hazel moth caterpillar
Human Uses of Lichens * Brown, purple and red fabric dyes (e. g. Scottish tweeds and tartans) * Indicators and stains (e. g. litmus and orcein) * Emergency foods, e. g. rock tripe (Umbilicaria) * Part of the daily diet, e. g. Lecanora esculenta (“manna”? ) in Iran, flour from Cetraria islandica (Iceland moss) in Scandinavian ship’s biscuits, Inuit “nirukkaq” - partly digested lichens from caribou & muskox stomachs in winter * Commercial production of sugar in Russia, WWII * ‘Iwatake (Umbilicaria esculanta) as delicacy in Japan * Food additive io retard spoilage
More uses of lichens - medicine, embalming and perfumery (see Richardson for details) * Many lichen extracts are inhibitory to the growth of Grampositive bacteria * Some are also effective against Mycobacterium tuberculosus * Oakmoss (Evernia prunastri) and Treemoss (Pseudoevernia furfuracea) are used in Europe to make fixatives for perfumes and soaps. * The antibiotic properties of lichens were exploited by the ancient Egyptians in their embalming procedures
Lichens and Weathering of Rocks Vertical section of Lecidea apothecium showing arching of shale laminae (Richardson) Lichen Acids
Some Crustose Lichens Caloplaca saxicola (Medlin) Xanthoria elegans (Medlin) Rhizocarpon geographicum (map lichen) (Medlin)
Some Foliose Lichens Cetraria arenaria, Medlin Parmelia sulcata, Medlin Pulmonaria lobata, Medlin Peltigera canina, Medlin
Some Fruticose Lichens Cladina rangiferina, Brodo Usnea hirta, Medlin Cladina stellaris, Medlin Teloschistes chrysophthalmus
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