Yes, lichens are a symbiotic relationship between ascomycetes and cyanobacteria. Lichens are a unique form of symbiosis, in which a fungus (ascomycete) and a photosynthetic partner (cyanobacteria) live together in a mutually beneficial relationship. The fungus provides protection and structure for the cyanobacteria, while the cyanobacteria provide food for the fungus. This relationship is beneficial for both partners, allowing them to survive in harsh environments that neither could survive on its own.

Symbiosis in lichens

Schematic cross section of lichen, a symbiosis between green algae and a fungus. 1. Thick layers of hyphaecalled cortex 2. green algae 3. Packed loosely hyphae 4. Anchoring hyphae called rizines.

symbiosis in lichens is the mutually useful symbiotic relationship in green algae and/or blue-green algae (cyanobacteria) living between the filaments of a fungusforming lichen.

living as one symbiote on a lichen seems to be a successful way for a fungus to obtain essential nutrients, as about 20% of all fungal species have acquired this way of life. The autotrophic the symbionts that occur in lichens are a wide variety of simple photosynthetic organisms, commonly and traditionally known as “algae”. These symbionts include both prokaryotic and eukaryotic organisms.

Overview of lichens

Main article: Lichen
Lichens it is fungus who discovered agriculture — Trevor Goward

AN lichen is a combination of fungi and/or algae and/or cyanobacteria that have a very different shape (morphology), physiologyand biochemistry than any of the constituent species growing separately. Algae or cyanobacteria benefit their fungal partner by producing organic carbon compounds through photosynthesis. In return, the fungal partner benefits the algae or cyanobacteria by protecting them from the environment by their filaments, which also collect moisture and nutrients from the environment and (usually) provide an anchor for it.

Most lichens contain eukaryotic autotrophs belonging to the Chlorophyta (green algae) or the Xanthophyta (yellow green algae). About 90% of all known lichens have a green alga as a symbiont. Among these, trebouxia is the most common genus, occurring in about 20% of all lichens. The second most commonly represented genus of green algae is Trentepolis. Overall, about 100 species are known to be autotrophic in lichens. All algae and cyanobacteria are believed to be able to survive separately as well as within the lichen; that is, there are currently no known algae or cyanobacteria that can only survive naturally as part of a lichen. Common partner algae are trebouxia, pseudotrebouxiaor Myrmecia.

Prokaryotes belong to cyanobacteriawhich are often called by the old name “blue-green algae”. Blue-green algae occur as symbionts in only about 8% of known lichens. The most commonly occurring genera of symbiotics cyanobacteria it is nostoc and Cytonema.


Both the lichen and fungal partner have the same scientific name, and lichens are being integrated into fungal classification schemes. Depending on the context, the taxonomic name may refer to the entire lichen or just the fungus that forms part of the lichen.

The alga or cyanobacterium has its own scientific name, which is unrelated to the name of the lichen or fungus.

fungus component

About 20% of all fungal species are capable of forming lichens. The fungal partner can be a ascomycete or basidiomycete. Overall, about 98% of lichens have an ascomycete mycobiont. Next to the Ascomycota, the greatest number of lichenized fungi occurs in the imperfect fungi. comparatively few basidiomycetes are lichenized, but these include fly agaricsas species of Lichenophaly, clavarioid fungias species of Multiclavulaand corticoid fungias species of Dictyonema.

The greatest number of lichenized fungi occurs in the Ascomycota, with about 40% of the species forming such an association. Some of these lichenized fungi occur in orders with non-lichenized fungi that live as saprotrophs or plant parasites (for example, the Leotiales, Dothidealesand pies).

Other lichen fungi occur in only five orders in which all members are engaged in this habit (Orders Graphidales, Gyalectales, peltigerales, pertusarialesand Teloschistales). Lichenized and non-lichenized fungi can even be found in the same genus or species.[citation needed]

photosynthetic component

The photosynthetic component of a lichen is called photobiont or phycobiont. The layer of tissue that contains the cells of the photobiont is called the “photobionic layer”.

Approximately 100 species of photosynthetic partners from 40 genera and 5 distinct classes (prokaryotic: Cyanophyceae; eukaryotic: Trebouxiophyceae, Phaeophyceae, Chlorophyceae) were associated with lichen-forming fungi.

A particular species of fungus and a species of algae are not always necessarily associated in a lichen. A fungus, for example, can form lichens with a variety of different algae. The stalk produced by a given fungal symbiont with its different partners will be similar, and the secondary metabolites identical, indicating that the fungus has the dominant role in determining lichen morphology. Furthermore, the same algal species can occur in association with different fungal partners. Lichens are known in which there is a fungus associated with two or even three species of algae. Rarely, the reverse can occur, and two or more fungal species can interact to form the same lichen.

green algae

About 90% of all known lichens have a green alga as a symbiont. “chlorococcoid” means a green algae (Chlorophyta) which has unique cells that are globose, which is common in lichens. This has already been sorted in order Chlorococcalesthat can be found in the older literature, but new DNA data show that there are many independent lines of evolution among this formerly large taxonomic group. Chlorococcales is now a relatively small order and may not include any lichen photobionts.

The term “Trebouxioid” refers to members of the trebouxia algae or other algae that resemble them: a chlorococcoid photobiont of green algae in the genus trebouxia. Algae that resemble members of the trebouxia presumably are in the class Trebouxiophyceae and use the same descriptive name (Trebouxioid). trebouxia has already been included here, but is now considered in a separate class Trebouxiophyceae.


Although photobionts are almost always green algae (chlorophyta), sometimes the lichen contains a blue-green algae (cyanobacterianot really an alga), and sometimes both types of photobionts are found in the same lichen.

AN cyanolichen is a lichen whose main photosynthetic component is a cyanobacterium (photobiont). Many cyanolichens are small and black, and have limestone as the substrate.

Another group of cyanolichens, the gelatinous lichens (for example, of the genus Collema or Leptogium) are large and leafy (for example, species of Peltigera, lobariaand Degelia. These lichen species are blue-grey, especially when moist or wet. Many of these characterize the Lobarion communities of areas of higher rainfall in the west of Great Britain, for example in the celtic rainforest.

parasitic fungi

Some fungi can only be found living on lichens like obligate parasites; They are not considered part of the lichen. These are referred to as “lichen fungi”.


Source: Symbiosis in lichens

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