There is convincing evidence that, over many centuries, people from many cultures in widespread parts of the world have eaten or drunk lichens or products derived from lichens. However, there is no evidence that lichens have consistently formed a major part of the diet within any society. Some lichens have been seen as delicacies but more often they appear to have been a food of last resort or have been used to eke out other food supplies. Rather than producing a long list of the many species that have been consumed by humans I will confine myself to a few examples which will give you some idea of the range of culinary uses of lichens.
In India a Parmelia species (known in Telugu as rathapu or 'rock flower') has been used as a curry and Lecanora esculenta has been eaten by inhabitants of the Middle Eastern deserts, with suggestions that this was the biblical manna. The evidence for this is weak. Nevertheless the expression manna lichen has been coined as an informal collective term for the small, terrestrial VAGRANT LICHENS of the Northern Hemisphere, though not all have been recorded as being eaten. Two examples of such manna lichens are shown in the photo (right) and you can read more about the subject in the DIYARBAKIR'S HEAVENLY BREAD CASE STUDY.
Cetraria islandica , even though a lichen, has been sold commercially as Icelandic Moss. It has been used as a constituent in broths or gruel and, when dried and ground to meal, mixed with ship's flour to make a bread reputedly less liable to weevil attack. Iceland Moss was also used in other ways, as shown by the following classified advertisement from the Sydney Morning Herald of Saturday of the 18th of April in 1863