Reproduction in Lichens
Reproduction in lichen takes place both by sexually and asexually.
Asexual reproduction takes place by following methods:
- Fragmentation:On maturity, the older portions of the thalli of lichens die and decay. The thallus breaks into pieces accidentally and each piece develops into a new plant. This occurs more frequently in pendant thallus, such as of Ramalina reticulate.
- By soredia:Soredia are spherical bundles of fungal filaments and algal cells that are produced in the algal region (usually the medulla) and rupture through the thallus to the outside. They give the thallus a powdery appearance. The soredia blow away and germinate to produce a new lichen. Aggregates of soredia on the lichen surface are called Somalia. Soredia may be laminal or marginal.
- Isidia: Isidia are tiny peg-like or finger-like structures containing fungal filaments and some photobiont cells. They are found on the surface of lichens and are nearly always laminal. Isidia break off and colonize new areas in a similar manner to soredia.
Sexual reproduction involves fungal partner of the lichen thallus. Most lichens resemble the fungi belonging to ascomycetes or basidiomycetes as they produce either ascospores or basidiospores.
Male reproductive organ ( Spermogonium );
The flask-shaped structure also called spermogonia or picnic. Found embedded in the thallus, opens outside by small pore called ostioles. The hype lining the inner surface of the spermogonium produce numerous non-motile gametes called spermatia which are set free in a slimy mass which oozes out through the ostioles.
Female reproductive organ ( Carpogonium );
Multicellular that develops in the medulla of the young lobes of the thallus. Consists two portions that are coiled portions having multicellular ascogonium and the upper straight portion also called trichogyne which is also multicellular.
At the point of contact between spermatia and trichogyne, wall dissolves and content of spermatium passes into trichogyne through a pore and male nucleus passes to the ascogonium and fuse with egg nucleus. Ascogenous developed from ascogonium and withering of the trichogyne, numerous sterile hyphae are developed forming the paraphyses in between the asci and finally ascocarp is formed which may be apothecium or perithecium consisting layer of fertile tissue called the hymenium. Each ascus consists of 8 ascospores which are variation in size, color, and form. During wet weather, the ascospore germinates hype which on coming contact with an appropriate algal cell makes the new lichen thallus.
- Lichens are complete organisms formed by a permanent and mutual or symbiotic association between an algae and a fungal partner.
- Soredia are the small microscopic structures formed on the lichen thallus.
- Isidia are small projections formed on the upper surface of the thallus. The isidia consist of an external cortical layer and an internal algal layer.
- The male reproductive organs are called spermogonia or pycnia which are flask-shaped structure.
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