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.
Growth form, size, shape of the thallus
, colour of cortex
of the lower cortex
and margin, pores and cracks of the upper cortex
Presence of vegetative propagules
; shape and colour of the apothecia
(if present), shape, number of cells, size, colour of the ascospores
Production of lichen compounds.
Distribution, elevation, habitat, substrate
The type of alga, either chlorophyta
Lichens can be divided into three basic forms depending on the form of the thallus
Crust-like, adhering tightly to the substrate
by their entire lower surface. Some endolithic lichens are embedded in their rock substrate.
Leaf-like with a distinct upper and lower surface which are attached to their substrate only by small root-like structures (rhizines
strands or hollow stalks called podetia
, usually attached to the substrate
at the base or holdfast.