Types of Lichens

Lichen Growth Forms

Crustose (crusty)

  • edges flat, unlobed and closely attached to substrate
  • hard to remove without damaging substrate or lichen
  • algae usually dispersed
  • edges unlobed (leprose and squamulose included here)

Foliose (leafy)

  • A sandwich of fungal layer with algal mat in middle
  • circular growth, lobes
  • small rootlets called rhizines attach it to substrate
  • top and bottom layers different

Fructicose (shrubby)

  • round branches with its fungal layer outside, its algal layer within
  • no rhizines
  • vertical growth pattern
  • odd-shaped structures such as globets; threads
  • Fruticose lichens are either shrub-like small mounds, growing up from the ground, or beard-like, small tangles looking a bit like spanish moss when hanging down, attached to the substrate only at their bases, and usually with a circular cross-section.

In addition, Leprose lichens are powdery masses with little or no organized structure; Squamulose are much the same as crustose, but have raised edges, which can be folded and lobe-like.

All but fruticose lichens grow slowly; their growth, about .5 to 5 mm per year measured by the expansion of their circles. Fruticose lichens, on the other hand grow vertically, and quickly, up to 2 cm per year. Left unchallenged, undisturbed and with a suitably long-lived substrate, it is quite common for a lichen to have a lifespan of several centuries; in fact a certain arctic specimen of a crustose lichen, Rhisocarpon geographicum, was found to be about 9000 years old!

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