Lichens exhibit a range of different growth forms: crustose, squamulose, leprose, foliose and fruticose. Cladonia are included as a separate group as they can exhibit both crustose, squamulose and fruticose growth forms.
Grouping lichens according to their growth type is an artifical system of classification, but it is a particularly useful aid to identification. Within each of the six types there are various subdivisions and a degree of overlap between the groups.