... and the protection of the lichen. The algal cells, through the process of photosynthesis provide the lichen with its organic nutrition. Lichens are photoautotrophs, so they obtain their organic nutrients using energy from sunlight. 1. The Cortex 2. The Algae Layer 3. The Pith 4. Under Cortex 5. The Rhizines The body of a lichen is termed the thallus, and its general shape enables us to group lichens into four broad categories. Crustose Lichens: Crustose lichens form a crust on the surface of the substrate on which they are growing. Crustose lichens tend to grow out from their edges and have their fruiting bodies in their centre. Crustose lichens are very difficult to remove from their substrates. An example of a crustose lichen is Pertusaria Multipuncta. Squamulose Lichens: Some lichens have a portion of their thallus removed from the substrate to form squamules. They have an upper cortex but no lower cortex. Cladonia cenotea is an example of a squamulose lichen. ...

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