The classification of lichen, like that of fungi, are undergoing constant change. There are about 15,000 described lichens which range in size from 1 mm to more then 3 meters, and come in many different colours and shapes. Most lichens are considered to be edible (or at least not poisonous). If not disturbed they can live for centuries.

Thallus characters:
Growth form, size, shape of the thallus, colour of cortex, rhizines and cilia of the lower cortex and margin, pores and cracks of the upper cortex.

Reproductive characters:
Presence of vegetative propagules; shape and colour of the apothecia (if present), shape, number of cells, size, colour of the ascospores.

Chemical characters:
Production of lichen compounds.

Ecological characters:
Distribution, elevation, habitat, substrate.

Algal host:
The type of alga, either chlorophyta or cyanobacteria.

Lichens can be divided into three basic forms depending on the form of the thallus.

Crustose:
Crust-like, adhering tightly to the substrate by their entire lower surface. Some endolithic lichens are embedded in their rock substrate.

Foliose:
Leaf-like with a distinct upper and lower surface which are attached to their substrate only by small root-like structures (rhizines)

Fruticose:
Shrub-like, pendulous strands or hollow stalks called podetia, usually attached to the substrate at the base or holdfast.