Cephalodium

Cephalodium (plural: cephalodia ) is a term from the lichen customer ( Lichenology ).

Cephalodia are demarcated areas in lichens, which in addition to fungus and green algae partners as secondary symbionts cyanobacteria ( blue-green algae ). These areas may be either in the thallus are inside (internal cephalodia ), or the bearing mount ( external cephalodia, the blue-green algae are separated by a layer of bark to the outside). Examples of external cephalodia found for example in some representatives of the Stereocaulaceae or Peltigeraceae. Thus, they can be seen as blue-black growths about when Apfelflechte ( Peltigera aphthous ). Internal cephalodia own example Nephroma arcticum or Solorina crocea. The blue-green algae partners can come from the genera Nostoc, Stigonema or Scytonema.

Advantages of this triple symbiosis are that the lichen ammonium as a nitrogen source is directly from the atmospheric nitrogen available to the blue-green algae partners can fix it with the enzyme nitrogenase. Nevertheless cephalodia are relatively rare and occur only in 3-4 % of all lichen species.