Lichens are found abundantly growing in various places like on rocks, walls, gravestones, on roofs, tree barks, soil, etc. Therefore, they are called the group of terrestrial organisms.
These organisms are symbiotic associations between an alga and a fungus partner, which are found in different colours, shapes, sizes and forms. According to records, lichens were found about 400 million years ago.
These terrestrial organisms require a fresh environment with adequate air for their growth and development. Other than the rocks, lichens are found on gravestones, on walls and in many other environmental conditions. In particular events, these organisms are also observed on tiny branchlets, flat leaf-like structures, a powder-like appearance and in various other forms.
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Classification of Lichens
There are various other types of lichens. Based on their certain special features, they are classified into different types.
Based on their growth
1. Crustose Lichens
Crustose lichens are flat, thin and without any distinct lobes. They are usually found closely attached to stones, rocks, barks and the trunk of trees. Haematomma puniceum and Graphic scripta are the best examples of crustose lichens.
2. Foliose Lichens
The foliose lichens are more attractive compared to other types of lichens. They are flat shaped, broad, smooth and leaf-like structures, which often resemble crinkled and twisted leaves. It holds a distinct upper and a lower surface. This type of lichens is generally found attached to rocks and twigs with the help of the rhizoid. Cetraria, Cluiudhuria, Parmelia and Xanthoria are a few examples of foliose lichens.
3. Fruticose Lichens
These are the most important types of lichens, which are thin and freely branched. The fruticose lichens constitute larger and attractive growths standing out from the branches of trees, foliage and rocks. Cladonia, Ramalina and Usnea are the common examples of fruticose lichens.
Based on their habitat:
- Lignicolous. These types of lichens live in the woods.
- Corticolous- These types of lichens live on the bark of trees.
- Saxicolous- These types of lichens live on stones or rocks.
- Marine. These types of lichens are found growing on the siliceous rocks, near the shores of the sea.
- Freshwater. These types of lichens are found growing on the hard siliceous rocks, especially around the freshwater.
- Terricolous- These types of lichens are found growing on the soil, therefore also called the terrestrial lichens.
Based on their internal structure:
- Heteromerous lichens
- Homoiomerous lichens.
Based on their fungal partner:
Also Refer: Economic Importance Of Lichens
This article concludes an introduction to Lichens and their classification. To know more about lichens, their types, significance, other related topics and important questions on Lichens, keep visiting our website at BYJU’S Biology.