Lichens General Information

Lichens are not a single entity but a community of at least 4 major organisms: algae, fungi,
bacteria and yeast. Imagine 4 different kinds of animals living in the same home! Over 19,000
lichen species have been discovered (Lücking et al., 2017). Among the 19,000 species, the fungi,
algae, yeast, or bacteria are in various combinations contributing to their amazing diversity.
Lichens are unique in their capacity to tolerate extremes, e.g. cold temperatures, lack of water,
and bright sunlight (Spribille et al. 2022). They can withstand conditions more adverse than
when each partner exists on its own as each partner contributes something that benefits the
group. In lichens, the algae produce sugars through photosynthesis that feeds the fungi, and
the fungi produces a protective layer that prevents the algae from drying out and dying
(Spribille et al.2022). Fungi also protect the algae from herbivory, and UV radiation (Spribille et
al. 2022). Bacteria and yeast seem to help keep the lichen healthy by providing some additional
nutrients, protecting against stress, and decomposing some of the older lichen body parts
(Aschenbrenner et al. 2016).

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Lichen Growth Forms

The primary feature for lichen identification is the growth form. All lichens begin with the
germination of a single spore and grow outwards in a circle. For lichens adhering to a rock or
tree this will be the most common shape you see, but the circular body (thallus) does not
describe the growth form. Growth form refers to how the lichen is attached to its substrate
(rock, soil or tree) and whether the body of the lichen is two-dimensional (appearing flat) or
three-dimensional (appearing bushy).

1. Crustose lichens are lichens where the outside edge of the lichen cannot be lifted from
   the rock or tree. To remove this lichen from the rock or tree you would need to remove
   a piece of the rock or tree bark, as the lichen grows between the mineral grains of the
   rock or within the surface layers of bark. These lichens look like paint that was splashed
   onto the rock surface or tree bark.
   2) Foliose lichens are lichens with an outer edge that you can liW up and peer underneath.
   The color and texture of the underside are important features used for identification.
   Undersides can be white, tan, or black. Texture can range from smooth to hairy with
   some having vein-like structures.
   3) Fruticose lichens are three-dimensional lichens. They have upright reproductive
   structures that vary in shape and color and are sometimes bright red.