Foliose lichen

A foliose lichen is a lichen with leafy body parts (thallus),^[1] and which generally have a "skin" (cortex) on each side of the leafy lichen body part (thallus). Crustose lichens (lichens that grow like a crust of paint on their substrate), and especially sqamulose crustose lichens, may not be attached to the substrate at the edges, giving a leafy appearance similar to foliose lichens, but there is no lower cortex on the leafy part. Fruticose lichens (lichens that have a form similar to a tiny leafless, branching shrub) may have the "branches" flattened, so as to appear leafy, but foliose lichens have a single cortex wrapping around the "branches", whereas foliose lichens generally have an upper and a lower cortex. Gelatinous lichens may appear leafy, but lack a cortex or internal structure, having the photobiotic component diffuse throughout the nonfruiting part of the lichen body, whereas in foliose lichens the algae are in a layer. In foliose lichens, the layer of tissue containing the photosynthetic component has the algae more diffuse in the fungus than in foliose lichens, where the algal layer is generally very distinct.

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