Asexual reproduction of lichens occurs through the production of spores.
(i) Soredium : Soredium is a tiny body of algae covered with fungi. It is dispersed by wind and germinates in favorable conditions to form new lichens.
(ii) Isidium : Isidium is a tiny papilla like spore. It grows and metamorphoses to form new lichens.
(iii) Pycnidium : Pycnidiospores are produced inside the pycnidium. Pycnidiospores germinate to form new lichens.
(iv) Phylidium : Leaf-like phyllidia are produced in foliose lichens. Lichens reproduce by phyllidia.

The reproduction method of lichen is-
1. Organogenesis: Organogenesis of lichens occurs by fragmentation and continuous process of death and decay.
2. Asexual reproduction: Asexual reproduction of lichens occurs through the production of spores.
(i) Soredium : Soredium is a tiny body of algae covered with fungi. It is dispersed by wind and germinates in favorable conditions to form new lichens.
(ii) Isidium : Isidium is a tiny papilla like spore. It grows and metamorphoses to form new lichens.
(iii) Pycnidium : Pycnidiospores are produced inside the pycnidium. Pycnidiospores germinate to form new lichens.
(iv) Phylidium : Leaf-like phyllidia are produced in foliose lichens. Lichens reproduce by phyllidia.
3. Sexual reproduction : The reproductive organs of lichens are ascocarps or basidiocarps. Sexual reproduction of lichens also occurs through plasmogamy. Male genitalia of lichens are called spermagonia and female genitalia are called carpogonia. Spermagonium produces pungametes and carpogonium produces strigametes. The male gamete and female gamete unite to form the zygote. The zygote germinates to form a new lichen.

The structure of a foliose lichen is described as-
1. Upper cortex: The uppermost layer of lichen is called upper cortex. It is formed by fungal hyphae. The hyphae are densely packed so there are no empty spaces. But if there is empty space it is filled by mucilage. This region is covered with cuticle. It is thick and acts like epidermis.
2. Algal layer: The next layer above the lichen cortex is called algal layer. Green or blue-green algae are abundant in these areas. Green algae include Chlorella, Pleurococus and blue green algae include Gleocapsa, Rivularia, Nostoc etc. Being green, this area produces food through the process of photosynthesis. The fungus absorbs nutrients from this region with the help of haustoria.
3. Medulla: The hollow area formed by fungal hyphae below the algal zone is called medulla. Hyphae divide into branches and spread in different directions. But the hyphae of the thallus are thin in the peripheral region and densely arranged in the central region. The hyphae in this region are called calaroplektenchyma.
4. Lower cortex: The lowest layer of lichen is called lower cortex. This area is densely populated. There are no blank spaces. The cells in this region are composed of pseudoparenchyma.
5. Rhizain: Multicellular basal rhizin is formed from the lower cortex region. Rhizine binds the thallus to a substrate and absorbs water and mineral salts.

Those lichens which have algae and fungi unequally are called heteromerous lichens. For example- Parmelia sulcata.

Lichens which contain algae and fungi equally are called homoiomeric. For example – Collema tenax.

(i) Homoiomerous : Lichens which contain algae and fungi equally are called homoiomeric. For example – Collema tenax.
(ii) Heteromerous : Those lichens which have algae and fungi unequally are called heteromerous lichens. For example- Parmelia sulcata.

Deuterolichen
If the lichen-forming fungi belong to the class of Deuteromycetes, they are called deuterolichens. Such as Racodium rupestre, Leparia incana etc.

If the lichen forming fungus belongs to the class Basidiomycetes then it is called Basidiolichen. For example – Clavaria mucida.

If the lichen forming fungus belongs to the class of Ascomycetes then it is called ascolichen. E.g. Rhizocarpon macrosporum.

(i) Ascolichen : If the lichen forming fungus belongs to the class of Ascomycetes then it is called ascolichen. E.g. Rhizocarpon macrosporum.
(ii) Basidiolichen : If the lichen forming fungus belongs to the class Basidiomycetes then it is called Basidiolichen. For example – Clavaria mucida.
(iii) Deuterolichen : If the lichen-forming fungi belong to the class of Deuteromycetes, they are called deuterolichens. Such as Racodium rupestre, Leparia incana etc.