Monterey Bay Aquarium Research Institute
Marine Botany

Caloplaca coralloides

Morphology


There are four major growth forms of lichens: foliose, fruticose, crustose and squamulose.

C. coralloides is a dwarf fruticose lichen, which means that it has a radial structure without a lower cortex (whereas many foliose lichens have a lower cortex) and that it generally grows in clumps up to 2 cm in diameter. C. coralloides has a shrubby thallus that can be greenish to yellowish to orangeish and with yellowy-orange apothecia that are disc shaped and can be concave, flat or convex. The “branches” of the thallus are somewhat cylindrical in shape and branch up to five times. The surface of the thallus is covered with little bumps that are the color of the thallus or a little lighter.


fruticose growth form

C. coralloides has pseudocyphellae, which are small round to angular holes that are .1-1mm diameter in the cortex.  

C. coralloides is anchored to its substratum by basal rhizoidal strands that are derived from the cortex.  The rhizines are ash gray and trap a powdery gray substance. Rhizines do not function as absorbing structures. However, they can sometimes function to trap water under the thallus of the lichen so that the thallus is exposed for longer to the water and can absorb more of it. Lichens also have no conductive tissue for rapid movement of water from one part of the thallus to another.



The thallus of a lichen consists of fungal hyphae, which are thread-like fungal cells, and algal cells. The hyphae are organized into different tissue layers:
  • -Upper cortex: ~ 30um thick. This is a dense layer of heavily gelatinized hyphae on the outer surface of the thallus that protects the lichen and can help slow water loss from evaporation. Lichens have no waxy cuticle like green plants.
  • -Hypothecium: densely branched, randomly oriented hyphae located underneath the upper cortex.

  • image of algal layer: green algae with nuclei
  • - Green algal layer: The photobiont of C. coralloides is a green alga. The most common green alga in lichens is Trebouxia. The algae are held within a mesh of fungal hyphae in a layer usually 10-50um thick. The hyphae around the photobionts are slightly expanded at the tips and pressed against the photobionts’ cell walls.
  • -Medulla: This is a loosely packed layer of hyphae that are not very gelatinized and have a large cell lumina. The medulla is where food reserves are stored in the lichen.


Lichens have special food-absorbing hyphal structures called haustoria that are associated with the algae. Different growth forms are associated with different types of haustoria. C. coralloides, like other fruticose lichens has haustoria that do not penetrate the algal cell. (In crustose lichens, haustoria are observed to penetrate the alga.)

cross section of apothecia zooming in on microscope picture of spores Sexually produced spores of the fungal component are colorless and two-celled, contained within sacs called asci within the hymenial layer of the apothecia. Apothecia are usually 0.4-2mm in diameter. The wall of the fruiting body is called the exciple. (For the morphology of reproductive structures see the section on sexual reproduction).


For the structure of vegetative structures, see asexual reproduction.

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2005 Megan Kelso

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