Reproduction In Lichens

Lichens reproduce through a combination of vegetative methods such as fragmentation, isidia, soredia, and cephalodia, as well as sexual reproduction involving structures like ascogonia, spermogonia, basidia, and spermatia.

Lichens Reproduction Structures

Lichens reproduce vegetatively or sexually by forming different reproductive structures that are:

1. Apothecia
2. Perithecia
3. Pycnidia
4. Isidia
5. Soredia
6. Blastidia
7. Lecanorine apothecia
8. Conidiomata
9. Ascogonia
10. Perigynia

Vegetative Reproduction In Lichens

Lichens reproduce vegetatively to propagate and colonize new areas. They do not depend on sexual reproduction for their survival. It reproduces by following methods:

1.      Fragmentation

Fragmentation is the most effective method of vegetative reproduction in lichens. It is commonly found in foliose and fruticose lichens. Mechanical stress or death of certain cells within the thallus leads to the breaking of the lichen body into fragments.

Each fragment contains growing areas. That are capable of developing into new thalli. For successful reproduction through fragmentation, it must have fragments of both the algal and fungal components.

2.      Isidia

Isidia are small, stalked outgrowths. These are present on the upper surface of the lichen thallus. These structures are composed of algal cells and fungal hyphae. It is surrounded by a protective cortical layer.

Unlike other reproductive structures, isidia remain attached to the thallus until they detach and disperse. Once they are detached, isidia can grow and develop into new thalli. Parmelia and Umbilicaria are the lichens that reproduce through isidia formation.

3.      Soredia

Soredia are small bud-like structures that form on the surface of the lichen thallus. They consist of numerous algal cells embedded within a mass of fungal hyphae. Soredia can occur within specific pustule-like structures called soralia or spread abundantly. They resemble a thin layer of greyish dust.

These structures are easily detached and can be dispersed by wind. When soredia land on a suitable substrate, they have the potential to develop into new lichen individuals. Parmelia and Bryoria are common lichens that reproduce through soredia.

4.      Cephalodia

Cephalodia are gall-like outgrowths that can be either external or internal in lichens. They have dark coloration and consist of fungal hyphae enclosed within algal cells. Cephalodia are not as commonly observed as other modes of reproduction, but they contribute to vegetative reproduction in certain lichens.

5.      Lobules

Some lichens, such as Parmelia and Peltigera, produce dorsiventral outgrowths known as lobules on the margins of their thalli. Lobules serve as organs of vegetative propagation and aid in the reproduction and expansion of the lichen.

6.      Phyllidia

Phyllidia are leaf or scale-like dorsiventral portions found in certain lichens, such as Peltigera. These structures act as propagules and help lichen to reproduce vegetatively.

7.      Blastidia

 Blastidia are yeast-like, segmented structures that can be observed in lichens like Physcia. These specialized structures function as propagules and help in vegetative propagation.

8.      Schizidia

Schizidia are scale-like structures found in lichens such as Parmelia. Similar to other propagules, schizidia are involved in vegetative reproduction.

9.      Hormocysts

Hormocysts are chain-like structures formed by the growth of algal and fungal hyphae together. Lichens like Lempholema utilize hormocysts as propagules for vegetative reproduction.

10.  Goniocysts

Goniocysts resemble unsoraliium-like structures and contribute to vegetative reproduction in certain lichens.

Asexual Reproduction In Lichens

Asexual reproduction takes place by pycnidiospores, conidia, and oidia formation.

Sexual Reproduction in Lichens

Sexual reproduction in lichens involves the fusion of specialized structures known as ascogonia and spermogonia in Ascolichens, and basidia and spermatia in Basidiolichens. Here’s a detailed explanation of the sexual reproduction process in lichens:

1. Ascolichens

In Ascolichens, the sexual reproduction process is similar to that of class Ascomycetes. The male reproductive organ is called the spermogonium, while the female reproductive organ is known as the carpogonium. These structures can develop on the same hypha or on different hyphae of the same mycelium.

a. Spermogonium

The spermogonia are flask-shaped structures that are embedded in the upper surface of the lichen thallus. They have a small pore called an ostiole, which serves as an opening to the outside. Within the cavity of the spermogonium, fertile hyphae produce small, rounded male cells called spermatia. In some lichen species, structures resembling pycnidia also function as spermogonia.

b. Carpogonium

The carpogonium, which is the female reproductive structure, consists of two parts. The lower part is a coiled multicellular portion called the ascogonium, while the upper part is a long, straight, thread-like structure known as the trichogyne. The ascogonium is located deep within the medullary portion of the lichen thallus, while the trichogyne emerges from the thallus and serves as a receptive structure for spermatia.

2. Basidiolichens

Basidiolichens exhibit sexual reproduction similar to that of Basidiomycetes. The specific structures involved in sexual reproduction in basidiolichens are basidia and spermatia.

a. Basidia

Basidia are the reproductive structures in basidiolichens. They produce basidiospores, which are involved in the sexual reproduction process. Basidia are responsible for the formation and dispersal of basidiospores.

b. Spermatia

Spermatia are male reproductive cells produced by the basidium. These small cells are involved in the fusion process during sexual reproduction in basidiolichens.

During sexual reproduction in lichens, the fusion of reproductive structures, such as the carpogonium and spermatia in Ascolichens or basidiospores in Basidiolichens, leads to the formation of fruiting bodies. These fruiting bodies, such as apothecia and endocarps, are responsible for the production and dispersal of sexual spores, which play a vital role in the reproductive cycle of lichens.

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