The foliose forms are flat, leaflike, and loosely attached to a surface.
Other common foliose genera include Cetraria, Parmelia, Peltigera, and Physcia.
A heteromerous thallus may have a stalked (fruticose), crustlike (crustose), or leafy (foliose) form; many transitional types exist.
The largest known lichens have a foliose form; species of Sticta may attain a diameter of about a metre.
Parmelia, largest genus of foliose (leafy) lichens, which includes among its members the species commonly known as crottle and skull lichen.
Fruticose lichens, which usually arise from a primary thallus of a different growth form (i.e., crustose, foliose), may be shrubby or pendulous or consist of upright stalks.
Crustose form varies: granular types such as Lepraria, for example, have no organized thalloid structure; but some Lecanora species have highly organized thalli, with lobes that resemble foliose lichens lacking a lower cortex.
Umbilicaria, called the common rock tripe, differs from other foliose forms in its mode of attachment in that its platelike thallus attaches at the centre to a rock surface.
Crottle, the largest foliose lichen, resembles crumpled leather and sometimes grows 90 to 120 centimetres in diameter.
Foliose lichens are large and leafy, reaching diameters of several feet in some species, and are usually attached to the substrate by their large platelike thalli at the centre.
The edges of foliose lichen rise up from the surfaces they grow on like the margins of curling paper.
