Lichens Flashcards
What are the photosynthetic partners to the fungi in a lichen?
Unicellular or filamentous green algae or less commonly cyanobacteria (which also fix N2)
What fungal phyla form lichens?
Ascomycetes (sac fungi)
Very few Basidiomycetes
Why are lichens given species names even if they are formed of different Kingdoms?
The meld of fungus and algae (or other photosynthetic partner) is so complete and each is unique that it needs to be given a species designation
How many lichen species have been described?
Over 25,000
What provides most of the lichen shape?
The fungal hyphae create the structure with cortex and medulla
Where is the algal component located in a lichen?
The inner layer below the fungal surface (upper cortex)
What is the reproductive structure of an ascomycete called? What is it called in a lichen?
- An Ascocarp
- An Apothecium (fruiting body)
What is an apothecium?
The fruiting structure of the ascomycete fungus in a lichen
- It is a cup-shaped, spore-producing structure
What are Soredia?
Granular or powdery asexual reproductive structures of the fungus and algae
What are Soredia made of and where are they produced?
Soredia are asexual reproductive structures composed of fungal hyphae and algal cells formed on the thallus where the cortex has ruptured
What do soredia need once they are released?
They need a suitable substrate for a new lichen colony to establish
What are Isidia?
- Small peg-shaped asexual reproductive structures
- Produced on the upper cortex of the thallus that easily break off
- Similar to Soredia
What does each partner provide in the lichen?
Each provides what the other cannot obtain on its own
- Alga cell leaks carbohydrate and provides fungus with food
- Fungus provides suitable habitat for photosynthetic partner growth
How does the fungus provide for the photosynthetic partner?
Offering suitable physical habitat by retaining water and minerals
- facilitates gas exchange
- Protects from intense UV
- Deters herbivores with toxic compounds
What is a lichen acid? What are their properties?
Fungi secrete acids by secondary metabolism
- Block UV
- Antimicrobial capabilities
- Bioaccumulate minerals (break down and sequester minerals)
What is the nature of the lichen symbiosis?
Mutual exploitation instead of mutual benefit
What environments to lichens live in?
Where neither the fungus or algae symbiont can live separately in abundance
- The fungi do not grow alone in the wild but algae may occur as free-living organism
What happens when each partner in a lichen is cultured separately?
Fungi do not produce lichen compounds
Algae do not leak carbohydrate food from cells
What is haustoria and what does it do?
Haustoria are part of the fungus hyphae that invade and kill algal cells, but before the algae can replenish their numbers
Why are lichens important for recently exposed surfaces?
Lichens are pioneers for colonizing newly exposed mineral soils and rock surfaces and start process of primary succession
- After forest fires
- Volcanic flows
- Newly deglaciated surfaces
How are lichens the pioneers of primary succession?
- Lichen acids penetrate outer crystals of rocks to help break them down
- Facilitate soil-trapping
- Nitrogen fixing lichens add organic nitrogen (ex. lungworts)
What are Rhizocarpon species good for?
Dating surfaces because they grow in concentric rings that can be counted to give a general idea of the age of a new surface that has been colonized by lichens
What is a fact of a true epiphyte?
A true epiphyte cannot live on the forest floor and will die if it falls off of branch or trunk
What happens to lichens in arid climates?
They don’t give up easily
They rapidly dehydrate and stop photosynthesis, grow slowly (<1mm/year)
Why are lichens important in grasslands?
They stabilize surfaces and prevent erosion and ‘dust-bowl’ scenarios
What happens to lichens in dry habitats?
They quickly absorb water from fog/rain and gain >10x their mass in water
Why is reindeer lichen (Cladonia rangiferina) significant?
- Provides winter food for ungulates (caribou and reindeer) in the arctic tundra
- A reduction in this lichen due to climate change would spell disaster for the herbivores
Why are lichens so successful?
They can tolerate severe temperatures and desiccation (and can provide food for some organisms in these climates)
What can lichens bioindicate?
Air quality
- Due to their ability to passively accumulate and retain contaminants, toxins, and heavy metals
- Can therefore be used as a cheap assay material as opposed to expensive equipment
How are lichens used as a bioindicator?
- Sensitive to air pollution and decrease serves as early warning of deteriorating air quality
- Early indicator before complete disappearance
- Can be assayed to determine heavy metal contamination
- Used in Index of Atmospheric Purity (IAP)
- Re-establishment can indicate cleaner air in previously contaminated area
IAP
Index of Atmospheric Purity
- Uses lichens as bioindicator
- Used by US forest service and air resource management programs
- Lichens are sampled at sites and assigned numerical values for characteristics such as frequency and cover
Foliose Lichen
- Flat leaf-like growth form
- Upper and lower cortex grow parallel to substrate
- Loosely attach to substrate usually by Rhizines on lower cortex
- Some may attach umbilicately
- Can be confused with Crustose sometimes but they do have a lower cortex with rhizines unlike crustose
What is an Umbilicate Lichen?
Attached to their substrate only at a central point by a cord
Crustose Lichen
- Growth form where entire lower surface is completely attached to substrate
- Lacks lower cortex and rhizines
- So tightly attached that they cannot be removed without damaging the substrate
- Must take substrate when removing lichen for ID (can’t just scrape off)
- Varied substrate types (rocks, trees, soils etc.)
- Called Saxicolous when upper cortex isn’t visible
What are Rhizines
Hyphae attachments that (loosely) attach a lichen to a surface
Crustose Lichens on rock
- Rock substrate type may indicate species (they have preferences)
- Different mineral content may affect which lichen type will grow there
- Most structure is inside the rock and cannot be seen (that is why substrate must be removed with lichen sample)
- Analogous to true fungus that is mostly invisible
Fruticose Lichen
- Shrub-like growth in an upwards direction
- Or Hanging growth in long strands often attached from a single point
- Most 3-dimensional lichen form
- Often round in cross-section (terete) and most are multi-branched
Terete
Term for describing a round cross-section in a lichen
Squamulose Lichen
- Scale-like lichen form with lobes called squamules that are small and overlapping
- Squamules form thallus and also occur on the podetia
- Some may have secondary compounds and pigments such as the red on the lip-stick lichen
- Ex. Pixie cup and Lipstick lichens
Podetia
Erect structures of Squamulose lichens that can have apothecia on the top of the podetia (pixie-cup or lipstick structure)
Chemical ID tests
- Lichens can be ID’d to species with chemical spot tests
- Spot test outer cortex or inner medulla
- Reaction may change colour and have a positive or negative result that can be used in a key
- Can also use a chromatogram on gel and test multiple reactions
Packets of algae and hyphae?
Soredia
What happens when a lichen is not lichenized enough?
It is too amorphous to be identifiable even though it may have the necessary components of a lichen
What can outcompete or damage a lichen?
Mosses can kill lichens and outcompete them in moist environments
- and fungus can kill non-lichenized lichens
