Lichens

Question 1

Lichen

Answer 1

A type of fungi

a symbiotic association of several Kingdoms that appear to have emergent properties

Don’t survive without algae (fungi can)

Question 2

Ascomyctes

Answer 2

Apothecium - cup-shaped, spore-producing structure formed by the fungal component of lichens.

Hyphae - provides most of the lichen’s mass and gives it its overall shape and structure (cortex and medulla).

Algal - usually occupies an inner layer below the fungal surface.

Question 3

Asexual Reproduction

Answer 3

• Soredia are granular or powdery asexual reproductive structures.
• They are comprised of fungal hyphae and algal cells that are produced on the thallus where the cortex has ruptured.
• If they land on a suitable substrate a new lichen colony will establish
• Isidia have the same function as soridea but are small peg shaped structures produced by the upper cortex of the thallus that easily break off.

Question 4

Partners involved in survival

Answer 4

In most cases, each partner provides what the other could not obtain on its own:

• The alga provides the fungus with food by “leaking” carbohydrate from their cells.
• The cyanobacteria provide organic nitrogen through N2 fixation.
• The fungus provides a suitable physical environment for algal and cyanobacterial growth by retaining water and minerals, facilitating for gas exchange, protection from intense UV and deterring herbivores with toxic compounds.
  - The fungi secrete acids by secondary metabolism and are known as lichen acids.

Question 5

Mutual exploitation

Answer 5

-The nature of lichen symbiosis is probably best described as mutual exploitation instead of mutual benefit.

-Lichens live in environments where neither the fungi or algae symbiot live separately in comparable abundance.
The fungi are do not grow alone in the wild; however, some lichen algae occur as free-living organisms.

• If cultured separately, the fungi do not produce lichen compounds and the algae do not “leak” carbohydrate from their cells.
• In some lichens, the fungus invades algal cells with haustoria (see arrow) and kills some of them, but not as fast as the algae replenish its numbers by reproduction.

Question 6

Help bring life to near landforms

Answer 6

• Lichens are important pioneers on recently exposed mineral soil and rock surfaces, such as after forest fires, newly deglaciated surfaces and volcanic flows.
• The lichen acids penetrate the outer crystals of rocks and help break down the rock (e.g., Rhizocarpon sp.).
• This facilitates soil-trapping and starts the process of primary and secondary succession.
• Nitrogen-fixing lichens also add organic nitrogen to some ecosystems (e.g., lungwort and coastal forests).

Question 7

Survival in extreme habitats

Answer 7

In dry - absorb a lot of water

• grow very slowly in the cold to save energy
• provide energy for caribou

Question 8

Bioindicators

Answer 8

Bioindicators of air quality, due to their ability to retain contaminants, mainly heavy metals.

can serve as an early warning of deteriorating air quality.

Question 9

Foliose

Answer 9

• A lichen growth form that is flat and leaf-like with an upper and lower cortex and often grow parallel to the substrate.
• They are relatively loosely attached to their substrates, usually by means of rhizines.
• Umbilicate lichens are attached to their substrate only at a central point (umbilicule cord is underneath, see arrows).

A lichen growth-form with a lower cortex and rhizines (hyphae attachment).

Some foliose lichens appear to look like crusts but close examination of the lower surface will reveal a lower cortex and rhizines.

Question 10

Crustose

Answer 10

• A lichen growth-form in which the thallus appears as a smear of paint because the entire lower surface is completely attached to the substrate and lacks a lower cortex and rhizines (hyphae attachment).
• Crustose lichens form crusts tightly attached to the substrate that they can’t be removed without damaging the substrate.

Referred to as saxicolous where upper cortex isn’t visible.

Question 11

Fruticose

Answer 11

• like little shrubs growing upward, or they can hang down in long strands, often attached form a single point.
• Fruticose lichens are the most three-dimensional. They’re are often round in cross section (terete), and most are multi-branched.

Question 12

Squamulose

Answer 12

-have scale-like lobes called squamules that are usually small and overlapping.

e.g., Pixie-cup and lip-stick lichens on decaying wood.
The squamules which form the thallus also occur on the erect structures called podetia (apothecia are found at the top of the podetia – red in the case of lip-stick).

Whole structure can be called podetia