How Do Lichens Impact Our Environment and Biodiversity?
Lichens are considered plant-like organisms that show symbiotic association with algae, till now there are 15,000 species of lichen. They mainly show symbiotic association with green algae or cyanobacteria and fungi (mostly ascomycetes and basidiomycetes). They are found all across the world depending on the condition of the environment. They are majorly found in colony form, like on the tree bark, exposed rock, and as a part of biological soil crust.
Lichens are also used as human beings as a source of food along with medicine extraction and dye. They are also considered a major source of food for reindeer that roam the far northern ranges.
Classification of Lichen
Lichens are classified into various types based on different factors. Some of the important types of classification of lichens are listed below
A. Based on their Growth -
Based on the growth of lichens, there are three types, they are
Crustose Lichens These lichens are thin, flat and don't have any distinct lobes. They are majorly found on the stones, rocks, barks and the trunk of trees. Some of the common examples of crustose lichens are Haematomma puniceum and Graphic scripta.
Foliose Lichens They are considered as one of the most attractive lichens and they are of flat shaped, broad, smooth and leaf-like structures, which often resemble crinkled and twisted leaves. They are generally attached with rocks and twigs with the help of rhizoids Some of the common examples of foliose are Cetraria, Cluiudhuria, Parmelia and Xanthoria
Fruticose Lichens These types of lichens are considered as one of the most important types of lichens and they are of thin nature and are freely branched. They are mainly grown on the branches of trees, foliage and rocks. Some of the common examples of fruticose lichens are Cladonia, Ramalina and Usnea.
B. Based on their Habitat -
Based on the nature of habitat lichen are classified into different types, they are:
Lignicolous: their presence is mainly on the wood.
Corticolous: Their presence is majorly on the bark of trees.
Saxicolous: Their presence is majorly on the stones or rocks.
Marine: They are mainly found 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: They mainly grow on the soil and because of this reason they are called terrestrial lichens.
C. Based on their Internal Structure -
On the basis of internal structure lichens are classified into two types
Heteromerous lichens
Homoiomerous lichens.
D. On the Basis of their Fungal Partner -
Ascolichens
Basidiolichens
Hymenolichens
Important Role of Lichens
Lichens are considered to be important in terms of economic and environmental factors. Some of the important roles of lichens are discussed below:
Some species of lichen play a crucial role in the conversion of rocks into soil, as they are helpful in soil formation and also improve the quality of the soil by enriching important nutrients which are helpful in plant growth.
They also play an important role in the nitrogen cycle as they help in fixing nitrogen from the atmosphere.
They are also considered to be an important source of food all over the world for human beings. Example Iceland miss is known to be an important source of food for Northern Europe and American continents.
With the help of lichens, Petrologists and Geologists are able to study and calculate the age.
They are also used as an important source of colouring agents and dyes. They are known to be good sources of natural dyes. For example, pH indicator is extracted from the lichens.
They are also helpful in the biodegradation of polyester, lead, copper, radionuclides and other pollutants polluting the planet earth.
They are also used in pharmaceutical industries and along with that, they are also helpful in making cosmetic products.
They are helpful in treating various types of skin-related disease like rashes.
Few species of lichens are also used in the degradation process of various pathogens and resources which lead to dangerous infectious disease in the human body and in plants also.
They are an important source of food for aquatic animals.
FAQs on Lichen: Meaning, Types, and Importance
1. What exactly is a lichen?
A lichen is not a single organism but a complex, composite organism that arises from a symbiotic association between a fungus and a photosynthetic partner. The fungal partner is called the mycobiont, and the photosynthetic partner, which is usually an alga or a cyanobacterium, is called the phycobiont. This unique partnership allows lichens to thrive in diverse and often harsh environments.
2. What is the nature of the symbiotic relationship in lichens?
The relationship in lichens is an example of mutualism, where both partners benefit. The fungus (mycobiont) provides the structural framework, protection from harsh conditions like UV radiation and dehydration, and absorbs water and mineral nutrients from the substrate. In return, the algal or cyanobacterial partner (phycobiont) performs photosynthesis to produce carbohydrates, which serve as food for the fungus.
3. How are lichens classified based on their growth forms?
Lichens are broadly classified into three main types based on the morphology of their thallus (body):
Crustose: These lichens form a thin, flat crust that is tightly attached to the substrate, such as rocks or tree bark, and cannot be separated without damaging it.
Foliose: These are leaf-like lichens with a flattened structure and distinct upper and lower surfaces. They are attached to the substrate by root-like structures called rhizines.
Fruticose: These lichens are shrub-like or hair-like, with branching, cylindrical, or flattened structures. They are either erect or hang from the substrate, attached only at the base.
4. Why are lichens often called pioneer species and excellent bioindicators?
Lichens are called pioneer species because they are among the first organisms to colonize bare rock and barren land. They initiate soil formation by trapping wind-blown particles and slowly breaking down the rock surface. They are considered excellent bioindicators, particularly for air quality, because they are extremely sensitive to pollutants like sulfur dioxide. Their decline or absence in an area is a strong indication of high atmospheric pollution.
5. How do lichens reproduce to ensure both partners are passed on?
Lichens primarily reproduce asexually through vegetative means to ensure the symbiotic unit remains intact. They produce specialized structures like soredia (powdery clusters of algal cells wrapped in fungal hyphae) and isidia (small, stalk-like outgrowths from the thallus). These fragments can be dispersed by wind, water, or animals to grow into new lichens. The fungal partner can also reproduce sexually by producing spores, but these spores must find a compatible algal partner to form a new lichen.
6. Is a lichen a plant, a fungus, or something else?
A lichen is not a plant or a fungus; it is a composite organism. While it contains a fungal component (the mycobiont), it is classified separately from both Kingdom Fungi and Kingdom Plantae. The presence of the photosynthetic partner (phycobiont) gives it plant-like capabilities (photosynthesis), but its overall structure and reproductive methods are dominated by the fungus. Biologically, it is treated as a unique symbiotic entity.
7. What are some important ecological and economic uses of lichens?
Ecologically, lichens are crucial for soil formation and provide food and shelter for various invertebrates. Economically, they have several uses:
Dyes: Litmus, the common acid-base indicator, is extracted from lichens like Roccella tinctoria.
Medicine: Some lichens, such as Usnea (Old Man's Beard), contain usnic acid, which has antibiotic properties and is used in traditional medicine.
Perfumes: Species like Evernia prunastri (Oakmoss) are used as fixatives in the perfume industry to help scents last longer.
