Lichens Classification

Lichens are a group of symbiotic organisms that can be broadly classified in two ways: one based on their growth form and the other based on their growth medium.

Based on their Growth

Lichens can be classified according to their growth form and physical appearance. The physical appearance of a lichen depends on its thallus, which is mainly composed of its fungal counterpart. These include:

• Foliose Lichens: These lichens have a leaf-like appearance.
• Fructose Lichens: These lichens have a branching appearance.
• Crustose Lichens: These lichens have flattened crust-like structures.
• Leprose Lichens: These lichens are powdery.
• Jelly Lichens: These lichens are characterized by a gelatinous appearance.
• Squamulose Lichens: These lichens often have a scaly appearance.

Also Read: Viruses, Viroids, Prions And Lichens

Based on their Habitat

Lichens can also be classified into subgroups based on their habitat or the medium they grow on. These include

• Terriculous Lichens: These lichens grow on terrestrial regions with soil.
• Aqueous Lichens: These lichens grow around areas near or under water. These are further divided into freshwater and marine lichens that grow on salicaceous rocks at the bottom or near the shores of the aqueous environment.
• Ligniculous Lichens: These lichens use dead wood as their substrate, such as twigs, branches, or stems. These woods have the bark stripped from it, and lichens utilize lignin as their growth medium
• Saxicolous Lichens: These lichens generally grow on hard substrates like rocks and stones.
• Corticulous Lichens: These lichens on tree bark attach and grow on trees.

Also Read: Difference Between Fungi and Lichens

Based on their Internal Structure

Lichens can also be classified into two types based on their internal structure and layers formed by their fungal and algae counterpart. There are

• Heteromerous Lichens: These are lichens in which the thallus is divided into four layers: three composed of fungi called upper cortex, lower cortex, and medulla, and one is made of algae.
• Homoimerous Lichens: Homoimerous lichens do not have distinct layers, and the algae are loosely arranged between the fungal components.

Also Read: Kingdom Fungi- Structure, Classification & Characteristics of Fungi

Based on their Fungal Partners

Lichens are composed of fungal and algal components and can be classified based on lichen fungal partners. These are

• Ascolichens: The fungal partner is of the fungal group Ascomycetes
• Basidiolichens: The fungal partner is of the fungal group Basidiomycetes.
• Deuterolichens: The fungal partner is of the fungal group Deuteromycetes.

Lichens, also known as lichen trees or lichen plants, are symbiotic associations between fungi and algae or cyanobacteria. The lichen types include – lichen crustose, lichen foliose, and lichen fruticose. Lichen is an example of mutualism.

The fungal component provides structure and protection, while the algal or cyanobacterial component contributes through photosynthesis. Lichens are highly adaptable and thrive in various environments, from arctic tundras to deserts.

Lichens play ecological roles such as soil stabilization, nitrogen fixation, and contributing to primary succession on bare substrates. In this article, we will read about Lichens, their general characteristics, structure, types, classification, and significance of lichen.