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Monterey Bay Aquarium Research Institute
Marine Botany

Caloplaca coralloides

Reproduction

Caloplaca coralloides can reproduce both sexually and asexually.

Sexual Reproduction:

An ascomycete with apothecia:

close up of apothecia of C. coralloidesCaloplaca coralloides is an ascomycete, which means that its fruiting bodies contain sacs, called asci, within which sexual fusion of nuclei takes place and spores develop. Some ascomycetes have fruiting bodies called apothecia while others have perithecia. Apothecia are disc or cup-shaped fruiting bodies in which the fertile tissue is exposed to the environment, whereas perithecia are flask shaped structures built into the thallus of the lichen in which the fertile tissue is less exposed. The fruiting bodies of C. coralloides are apothecia. The apothecia of C. coralloides are bright orange-ish yellow and are 0.4-2 mm wide.  The picture to the left shows apothecia of C. Coralloides.  The brighter orange circle in the center of the discs is the fertile layer, called the hymenium.  Surrounding the hymenium is the exciple, the wall of the apothecia.  Outside of the exciple is a layer of the thallus, which is more yellowy orange.

Where does the apothecium harbor its spores?

scanning electron micrograph of cross section of apothecium showing hymenium, hypothecium, algal layer and medulla.The structure of the fruiting body of the lichen is determined by the fungal component. The upper tissue layer is the hymenium, made up of thread-like hyphae (paraphyses) and small sacs called asci. The hymenium is generally 65-90 um thick and the paraphyses are simple or occasionally branched.  It is within the asci that sexual fusion of fungal cell nuclei takes place, followed by meiosis and mitosis, and resulting in the development of 8 ascospores (each 10-16 x 5-7um). When the spores are mature and environmental conditions are good for spore germination (when it is wet), the walls of the asci soak up water and swell. This structural pressure is used to shoot the spores out of the apothecium into the environment. Therefore, lichen need water to reproduce sexually.

*Cross section of C. Coralloides apothecium taken
with scanning electron microscope with the help of
Chris Patton, Hopkins Marine Station, Monterey, California.

Spores:

light microscope picture of ascospores in relation to tips of paraphysesThe sexually produced lichen spores in the apothecia are spores of the fungal component of the lichen. Only the fungal component of the lichen reproduces sexually. The lichenized algae reproduce by mitosis and are not packaged with the sexually produced fungal spores. Therefore, the lichen spores do not have everything that they need to grow into new lichens. Once the spores are released from the apothecium, land on a suitable substratum and germinate, they need to encounter an appropriate algal cell. Only then can the symbiosis be recreated. This is a picture of the sexually produced lichen spores of C. coralloides. They are colorless, two-celled and ellipsoid.

Pycnidia:

structure of pycnidia with conidia, pencil drawing Another group of structures that are important in sexual reproduction of lichen are the pycnidia. Pycnidia occur in all lichen groups. They are flask shaped structures embedded in the thallus of the lichen (similar in shape and size to perithecia) that produce hundreds of little flecks of fungal hyphae called conidia. Conidia can function as male spermatia, fusing with the “female” nucleus in the asci. However, conidia can also function as asexual fungal spores by falling onto the substratum, germinating, encountering a suitable alga and forming another lichen.

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2005 Megan Kelso

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