Lichen morphology

Lichen morphology refers to the physical characteristics and structures of lichen, a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship. The combined lichen has properties different from those of its component organisms.

Thallus forms and structures

The body of a lichen, known as the thallus, is typically formed of layers. The layers differ among the various types of lichens, which include crustose, foliose, fruticose, leprose, and squamulose.

Crustose

Crustose lichens, or crust lichens, are typically flat and form a crust-like covering that is tightly attached to the substrate, which can be rock, soil, bark, or leaves.

Foliose

Foliose lichens have a leafy appearance. They are somewhat flat, and the thallus is not tightly bound to the substrate, allowing for a bit of movement.

Fruticose

Fruticose lichens are free-standing and have a cylindrical structure. They can be either branched or unbranched.

Leprose and Squamulose

Leprose lichens have a powdery appearance, while squamulose lichens have scale-like lobes.

Reproductive structures

Lichens reproduce either sexually or asexually. Sexual reproduction involves the formation of fungal spores, while asexual reproduction can occur through the dispersal of diaspores, which are parts of the lichen body that can grow into a new organism.

Apothecia

Apothecia are the most common form of sexual reproductive structure in lichens. They are typically disc-shaped, but can also be convex. The disc contains the hymenium, the spore-producing layer.

Perithecia

Perithecia are flask-shaped structures that are embedded in the thallus. The spores are produced in the interior and are released through a small opening at the top.

Pycnidia

Pycnidia are small, flask-shaped structures that produce conidia, a type of asexual spore.

Ecological roles

Lichens play important roles in their ecosystems. They are pioneers on bare rock and soil surfaces, where they help to initiate soil formation. They also contribute to the nutrient cycle, particularly of nitrogen, through biological nitrogen fixation.

See also

• Lichenology
• Lichenometry
• Lichen substances