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  >13,500 species of lichens recognized Make up 20% of all known fungal taxa  Most mycobionts are either zygomycetes or ascomucetes Relatively few basidiomycetes

Photobionts  Only approx. 10% of lichens have a cyanobacterium photobiont The other 90% are algae  Photobiont/mycobiont interface is wall-to- wall (abut each other) or intracellular (fungus invades cell wall of algae)

Lichen thalli (body)  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 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

Types of lichens  Non-stratified Photobiont cells evenly distributed throughout thallus Leptogium Collema

Types of lichens  Stratified Differentiated into cortex (upper only, or upper and lower) and medulla  Cortex is made up of individual fungal cells  Medulla is a dense fungal mycellium Photobiont cells form a discrete layer just under upper cortex

Foliose lichens - Flattened, leaf-like thallus with an upper and lower cortex Peltigera elizabethae

Leprose lichens – aka dust lichens - Lack both upper and lower cortex, medulla attached directly to substrate  Lobaria pulmonaria--Lungwort

Crustose lichens - Lacking a lower cortex, attached to soil, rock or bark by hyphae of the medulla XanthoparmeliaUmbilicaria

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

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

Lichens as pioneers  Typically one of first vegetation to inhabit a new environment Occurs if there is new land due to volcanic eruption or large scale fire damage Begins on rock formation or loose soil  The basic nature of lichens allows them to easily attach to rocks and soil  Able to break down rocks to obtain some nutrients  As more rocks are broken down by lichens, more dominant plant species are able to take over the environment

Lichens as components of soil crusts Images from