PHYCOLOGICAL SOCIETY OF AMERICA
There are four major growth forms of lichens: foliose, fruticose, crustose
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
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
-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.
- 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
other fruticose lichens has haustoria that do not penetrate the algal
cell. (In crustose lichens, haustoria are observed to penetrate the
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
For the structure of vegetative structures, see asexual
2005 Megan Kelso