Introduction to lichens Flashcards
What are lichens?
“Stable consistent and identifiable mutualistic associations between algae and/or cyanobacteria (the phycobiont) and fungi (the mycobiont).” (Dobson, 2011)
Lichens are resurrection plants and some can even survive periods of desiccation.
Mycobiont = fungus -provides shelter and minerals for the alga
Phycobiont = algal or cyanobacterial partner - supplies fungus with carbohydrates (stored as mannitol)
Lichens are named by their fungal partner
^ Not that simple – we now know they often have yeast associations also
Yellow lichens seen on the roadside are tolerant to high pollution levels and not seen in less polluted areas. Reddish lichens are more common at high altitude high in protective carotenoid pigments.
What are lichens? Forms of thallus
Normally heteromerous and sometimes homoiomerous
see diagram: http://www.buffelskloof.info/Lichens.htm
The fungus makes up 95% of the mass with algae distributed within it.
Differing structures develop depending on thallus type
What are lichens? Recent findings: yeast interactions
Many lichens also have specific basidiomycete yeasts embedded in the cortex (outer layer)
*abundance correlates with phenotype variations
*yeast lineages are linked with specific lichens despite geographical separation
What are lichens? crustose, folliculose, fructicose
Some are crustose:
Can be scraped off the surface it grows on.
e.g. Map lichen (Rhizocarpon geographicum) is often used for date associations
some are folliculose:
close to the surface but not as tightly attached
e.g. Umbilicaria can be eaten as a survival food (found in arctic)
e.g. Xanthoria sp. Is very tolerant to high pollution – seen along road sides
some are fructicose:
Fruticose are seen in dense forest (feathery and branching) and coastal regions (appearing more like seaweed)
What are lichens? Algae with fungal partners
Fungal partners:
In the UK there are 270 fungal species that can form a lichen with algae
- Mainly ascocarp funghi associate with lichens
- May reproduce sexually or asexually
Algal partners:
approx. 30 genera of algae worldwide can enter into a relationship with funghi
3 main groups – unicellular green algae (partners in 60% of lichens)
- Trentepholia filamentous algae usually forms crustose lichens (~30% lichens)
- Cyanobacteria – prokaryotic and infact eubacteria despite being referred to as blue-green algae. Have a hydrothermic sheath to maintain moisture for photosynthesis
- 5% of lichens have a cyanobacteria
An overview of lichen reproduction
(see diagram)
fungus can germinate but will only be able to grow if it can form a relationship with an algae (lichenisation) or find other food – and other food is uncommon in lichen suitable areas.
Lichen reproduction: asexual reproduction: Isidia
Isidia are little outgrowths that break off and are transported by water or wind to grow in a new location.
Vertical section of isidia of Parmelia scortea, early (A) and late (B) in development
http://www.lichens.lastdragon.org/faq/lichen_asexual_dispersal.html
Lichen reproduction: asexual reproduction: Soredia
Soredia again are fragments of lichen tissue, they collect in cups and are usually transported by water splashing them out of the cups.
http://www.lichens.lastdragon.org/faq/lichen_asexual_dispersal.html
Lichen reproduction: sexual reproduction
http://www.plantpath.cornell.edu/glossary/defs_a.htm
Apothecia (sexual reproductive parts) come in many shapes, sizes and colours.
Lichens as pioneers: acquiring a foothold
Crustose lichens tend to colonise first
Foliose lichens coat them
Finally grasses take root and outcompete the lichens
Lichens as pioneers – Krakatua lithosere
*Erupted in 1883 – now only remnants remain
*New island of Anak Krakatua interesting to biologists for study of primary succession
*Cyanobacteria appear first and then lichens, mosses, angiosperms…
Lichens as pioneers: environmental factors affecting growth
Not necessarily an indicator of clean air – some grow in polluted areas
factors that affect growth:
*Nutrient levels
*pH of substrate (rock, wood or man-made) barks of different trees have diff pH
*Salinity
*Aspect
*Air pollution
^ Leads to formation of distinct communities filling different ecological niches
Lichens as extremophiles: wet and dry
Anaptychia runcinata can tolerate saturated conditions
^green edges are the wettest where a lot of photosynthesis occurs
Lichens as extremophiles: UV irradiation
e.g. ‘Elegant sunburst’ grows worldwide at high altitudes, carotenoid pigments protect it from UV and give it the red colour.
Found to be the most resilient under space radiation
More at: https://heatherkellyblog.wordpress.com/2015/01/12/more-weird-and-wonderful-lichens/
Lichens as extremophiles: Heavy metals
Stereocaulon delisei only grows on Zn/Pb-rich mine waste
such as in Cumbria.
^ Only grows in areas with high zinc and lead pollution.
