Types of lichens are:

1. Based on fungal components:

(a) Ascolichens:

In this category, the fungal partner belongs to Ascomycetes group of fungi.

(b) Basidiolichens:

Here, the fungal partner belongs to Basidiomycetes group of fungi.

(c) Deuterolichens:

In this category, the fungal partner belongs to Deuteromycetes group of fungi.

2. Based on their forms:

(a) Crustose lichen: These lichens show crust-like growth. These lichens grow on rocks and bark of the trees,

e. g. Graphis, Lecanora, Haematomma, etc.

(b) Foliose lichen: 

These lichens grow on trees in the hilly regions. The thallus is like a dry forked leaf,

e. g. Parmelia, Collema, Peltigera 

(c) Fruticose lichen:

These lichens are seen on the branches of trees hanging down. They are cylindrical, well branched and pendulous, with hair-like outgrowths, 

e. g. Usnea, Cladonia, Alectoria, etc.

3. Economic importance of lichens: 

(a) Lichen as food and fodder:

Many species of lichens are used as food by animals including man. Lichens contain a substance lichenin which is similar to carbohydrate making them edible. Parmelia is used in curry powder in India. Lichens like Cladonia, Citraria, Evernia, Parmelia are used as fodder as they form a favourite food for reindeers and cattles.

(b) Lichens in medicine:

Lichens contain usnic acid due to which they are used in medicines. Usnea and Cladonia species are used as an antibiotic against Gram positive bacteria.

Species like Lobaria, Citraria are useful in respiratory disease like T.B., Peltigera is useful in hydrophobia, Parmelia is used in treatment of epilepsy, whereas Usnea is used in urinary disease. Some lichens are also used in medicine due to their anticarcinogenic property.

(c) Industrial use of lichens: 

1. Lichens are used in various dyes for colouring fabrics.

2. Species like Rocella and Lasallia are used in preparation of litmus paper which is acid-base indicator.

3. In Sweden and Russia, lichens are used for production of alcohol.

4. Orcein is a biological stain obtained from Orchrolechia androgyna and O. tortaria.

5. Some lichens are also used in tanning process in leather industry.

6. Evernia and Ramalina are the sources of essential oils which are used in preparation of soaps and other cosmetics.

(d) Other uses of lichens: 

1. Lichens are used in cosmetics. 

2. Some lichens like Everniaprunastri also known as oakmoss is used in making perfumes. 

3. Lichen is also used as a preservative for beer.