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How do lichens reproduce?

Answer
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Hint: The lichens are the combination of two organisms that are algae or cyanobacteria and fungi. They live in a mutualistic relationship. The algae or cyanobacteria live in the filaments of multiple fungi species.

Complete answer:
The lichens can be reproduced by asexual mode, sexual mode and through vegetative parts:

Asexual reproduction:
By sporulation: Few lichens can reproduce by the means of oidia, conidia and pycniospores. This type of reproduction rarely occurred. Oidia are formed when hyphae break down into small pieces whereas pycniospores are produced inside the structure called pycnidia. The pycnidia open into the small pore called ostiole and a pycnidial wall made up sterile fungal hyphae. The fertile hyphae obstruct the sexual spores inside the tips of the pycnidia. After they fall on the correct substratum, the pycnidiospores germinate and come in contact with suitable algae. Finally, they develop into new lichens.

Sexual reproduction:
The sexual type of reproduction can be seen in ascolichens and basidiolichen which belong to the class Ascomycetes and basidiomycetes respectively. In this section will discuss ascolichens. On dissemination, the spermatia stick on the protruding tip of trichogyne and get withers after fertilization. The freely branched acrogenous hyphae are produced by the ascogonium and at the end the hyphae produce asci. All the structure surrounded by the sterile hyphae after fertilization which is resulting in the formation of a fruiting body. The ascospores are formed inside the asci. These spores can be separate or simple. They are very light in weight hence; they can be disseminated by wind over a long distance. After they fall on the correct substratum it germinates and forms fungal hyphae. When these hyphae come in contact with the suitable algal component they grow into a new lichen thallus.

Vegetative reproduction:
By soredia: They are small projections produced on the upper surface by the thallus. The soredia emerges from the algal zone below the upper cortex. The algal zone cells are divided actively and soon enclosed by fungal hyphae. After falling on the appropriate substratum, they developed into the new lichens. It is the most common method. There are several other methods of vegetative reproduction such as by fragmentation, Isidia and lobules.

Note: In sexual reproduction, the male reproductive part is called spermatogonia and female reproductive part is called carpogonium. They can present either on the same hyphae or the different hyphae of the same mycelium.