Foliose: leaf-like group
Introduction to the Foliose Group
Much of the foliose thallus is in contact with the substrate except the leaf-like lobes which, being curled up, may be easily removed. They might be paper thin when dry but swollen when wet. The dry and wet specimens may also have distinctly different colours
They are dorsiventral: have very different upper and lower surfaces and it is this feature which distinguishes the group from fruticose.
The difference in colour of the upper and lower surfaces (which is the fungal cortex) and, the colour and shape of root like stuctures (rhizines) are used in this group's identification.
Although Evernia prunastri "Oak Moss" is technically foliose, I have placed it with the fruticose group. Not only is it found with lichens in the fruticose group, it is also more difficult to distinguish it from genera within that group than it is from others of its own group.
Grey-green thallus with loosely attached lobes 15mm wide. The edges of the lobes are wavy and raised up. The underside is black with the exception of the region near to the edge of the lobe which is brown. Rhizines are simple (unbranched) and black.
Test with potassium hydroxide solution gives a positive result of yellow (K+y).
Peltigera polydactyla, one of the dog lichens
Large thallus, brown when wet, grey when dry. Underside white with white rhizines. Spore producing structures (apothecia), orange/brown standing erect at the lobe ends and with their margins curled over
The long narrow apothecia distinguishes the polydactyla from the canina where they are short and broad (Dobson 2011 p 315)
Dobson says that P. canina once used for treating rabies. A doctrine of signatures indication from the canine tooth-like the rhizines.
Hypogymnia physodesdescriptive text
Parmelia saxatilis, Crottle
Once collected to make a reddish-brown dye for wool.