Reproduction in Lichens (With Simple Diagram) | Lichenology

In this article we will discuss about reproduction in lichens:- vegetative reproduction in lichens, asexual reproduction in lichens and sexual reproduction in lichens

Reproduction in Lichens

• The lichens can reproduce in three methods: vegetative, asexual and sexual reproduction.

1. Vegetative Reproduction in Lichens

• Vegetative reproduction in lichens takes place by following methods:-

A. Fragmentation

• The thallus break into smaller pieces and each fragments will give rise to new thallus.
• These new thallus are genetically identical to the parent.
• This method is very common in pendant thalli.
• E.g., Ramalina reticulata.

B. Isidia

• Isidia are small, branched, spiny and elongated outgrowths from the thallus
• They contains both algal and fungal cells and covered by cortical layer.
• When detached, each isidium has the potential to grow into a new thallus under suitable conditions.
• E.g., Peltigera

C. Soredia

• Soredia are tiny, powdery granules or bud-like outgrowths typically found on the upper surface or edges of the thalli.
• Each soredium consists of few algal cells covered by fungal hyphae.
• When soredia detach from the thallus, they are dispersed by wind.
• On favourable condition, they germinate and form a new thallus
• E.g., Parmedia

2. Asexual Reproduction in Lichens

• In lichens, asexual reproduction is limited to the fungal component.

Conidia

• The fungal partner produces flask-shaped cavities known as pycnidia
• These pycnidia have a narrow opening called an ostiole.
• Within this the pycnidium, elongated hyphae known as pycnidiophores are formed.
• Tip of the pycnidiophores are produce chains of non-motile, single-celled conidia.
• Due to their lightweight and dry nature, these conidia are easily dispersed by wind
• Under favourable condition, conidia germinate and produce hyphae.
• E.g., Peltigera, Roccella

3. Sexual Reproduction in Lichens

• In lichens, Only the mycobiont partner reproduce sexually.
• The male reproductive structure is called spermogonium, while the female structure is known as the carpogonium.

The Male Sex organs (Spermogonium)

• Spermogonia form within flask-shaped cavities located on the upper surface of the thallus.
• These cavities open to the outside through a small pore known as an ostiole.
• Numerous hyphae arise from the cavity walls, with some being sterile and others fertile.
• The fertile hyphae generate non-motile male gametes called spermatia.
• These spermatia are released in a slimy mass through the ostiole.

The female sex organs (carpogonium)

• The carpogonium develops from hyphae situated deep within the algal layer.
• It consists of two parts: the upper, straight part known as the trichogyne and the lower, coiled part called oogonium.
• The oogonium is located deep within the medullary region of the thallus.
• The terminal part of the trichogyne end with an elongated cell that extends beyond the thallus surface and features a gelatinous cell wall.

Fertilization

• The spermatium released from the spermogonium, adheres to the sticky protruding part of the trichogyne.
• Following the dissolution of the common wall, the nucleus of the spermatium migrates into the carpogonium, where it fuses with the female nucleus.
• This fertilization process leads to the development of fruiting bodies
• The type of fruiting body is determined by the fungus associated with the lichen.
• The fungal partner can be either ascomycetes or basidiomycetes.

Ascholichens

• Numerous ascogenous hyphae emerge from the basal region of the fertilized oogonium.
• The diploid nucleus undergoes meiotic division, resulting in the formation of eight haploid ascospores and asci.
• The hymenium consists of asci and paraphyses.
• In Ascholichens, the fruiting body may be either apothecia or perithecia

I. Apothecium

• It is cup-like structure and have a layer of fertile tissues called hymenium or thecium.
• The hymenium is composed of sterile, hair-like hyphae called paraphyses, which are interspersed among sac like asci that contain the ascospores.
• Typically, each ascus contain eight ascospores.
• The asci are freely exposed out side at maturity.

II. Perithecium

• Perithecia are typically flask-shaped reproductive structures.
• They appear as small black dots on the surface of lichen.
• At maturity, a small opening at the apex known as an ostiole, facilitates the release of ascospores.
• Once the ascospores are liberated from the ascus, they germinate in a suitable environment and leading to the formation of new hyphae.

Basidiolichens

• Following fertilization, the diploid nucleus undergoes meiosis, resulting in the formation of four haploid nuclei.
• Each haploid nucleus migrates into a small projection called a sterigma, which protrudes from the basidium.
• A cell wall develops around each haploid nucleus, resulting in the formation of a basidiospore.
• These basidiospores are released from the sterigmata and are dispersed by wind or other means.
• When a basidiospore lands in a suitable environment, it germinates and giving rise to a new hypha.

Deuterolichens

• They are commonly called as lichen imperfectii
• In this lichens, their fungal partners belonging to the Deuteromycotina division of fungi.
• Sexual reproduction is absent in this group of lichens.

Conclusion

• Ascolichens: This is the most common lichen, they have sac-like reproductive structures known as asci (ascocarps), which produce ascospores.
• Basidiolichens: This type lichen has club-shaped reproductive structures known as basidia (basidiocarps), it is responsible for the production of basidiospores.
• Deuteromycetes: This group lichens lack sexual reproduction and primarily reproduce through conidia.