Rock tripe is a common name for edible rock-dwelling lichens, especially species of Umbilicaria. The term is vernacular rather than taxonomic, and its scope has varied by region and source. In North America, rock tripe was known primarily as a famine food, eaten by Cree, Inuit, and other Indigenous peoples and later by European explorers and voyageurs during periods of extreme scarcity. In East Asia, by contrast, Umbilicaria esculenta has been valued as a delicacy in Japanese, Korean, and Chinese cuisine since at least the 17th century. The English name derives from the Canadian French expression tripe de roche. Rock tripe requires extensive processing, typically soaking and repeated boiling, to reduce bitter secondary metabolites such as gyrophoric acid that otherwise cause severe gastrointestinal distress. The principal carbohydrate in Umbilicaria is pustulan, which humans digest poorly, so the lichens provide less usable nourishment than their dry mass might suggest. They also contain bitter secondary metabolites, especially gyrophoric acid, which may help explain the nausea and bowel complaints described in historical accounts. Rock tripe is best known in Western historical writing for its role during John Franklin's disastrous overland Arctic expedition of 1819–1822, when it was one of the few available foods as the party retreated across the Barren Grounds. Because Umbilicaria lichens grow very slowly, heavy harvesting can deplete local populations for long periods.
Terminology Historical lexicography defines rock tripe as an edible lichen of the genus Umbilicaria, or less often of the former genus Gyrophora. The same source describes the lichen as having a leathery thallus (body) attached to rock by a threadlike holdfast (anchoring structure). The English name derives from Canadian French tripe de roche. Because the term is a common name rather than a formal taxonomic one, it has been used somewhat loosely in historical writing.
Lichens involved The lichens most often meant by "rock tripe" are species of Umbilicaria, foliose (leafy) lichens attached to exposed rock by a central umbilicus. In North American food and expedition accounts, however, the lichen is often mentioned without precise species identification. A well-documented food species is U. esculenta, known as an edible lichen in Japan, Korea, and China. The names iwatake in Japan, seogi in Korea, and shí'ěr in China have been used for that species. In British and European usage, the closely related genus Lasallia is also sometimes included under the name, while in North America species of Lasallia are more often distinguished as "toadskin" lichens.
Use as food
North America
In North America, rock tripe was mainly a fallback food rather than a preferred staple, and Turner and Davis listed it among the famine foods of northwestern North America. It was eaten by Cree, Chipewyan, Inuit, and other Indigenous peoples. In northern Saskatchewan, the Western Woods Cree used rock tripe as a thickener for stews and gravies. Preparation typically involved gathering the lichen from rocks, washing it, breaking it into pieces, and boiling it in soups or broths; it was combined with fish, fish roe, or caribou blood, and one account describes "stone moss" being boiled with flour, lard, and salt. Indigenous people later introduced rock tripe to European explorers, Jesuit missionaries, and voyageurs in the Canadian subarctic, where it became a recognized, if dreaded, emergency food during periods of severe shortage. Turner and Davis associated its use with severe gastrointestinal pain.
East Asia In East Asia, by contrast, U. esculenta has long been treated as food in its own right rather than merely as an emergency ration. A 1643 Japanese cookbook, Ryōri Monogatari, already mentions it. In East Asia it is known as iwatake or wawatake and has been described as a delicacy used in dishes such as salads, soups, and fried preparations. Isao Yoshimura noted that Umbilicaria esculenta had long been known in Japan by the name iwatake, literally "rock mushroom", and that people were already using it as food well before Miyoshi formally described the species in 1893. He also recorded a southern Kyushu name, gantare-naba, meaning 'false mushroom'. Evgeny Davydov and Yoshihito Ohmura also recorded the Korean name seogi and the Chinese name shí'ěr for the same species. According to Yoshimura, early Japanese culinary literature included recipes for iwatake, including preparations boiled with sugar and soy, teacakes, and dishes made after scalding it with hot water. The difficulty and danger of gathering iwatake from cliff faces made it a subject of popular interest in Edo-period Japan. Utagawa Hiroshige II's 1860 woodblock print Iwatake Gathering at Kumano in Kishū, from the series One Hundred Famous Views in the Various Provinces, depicts collectors suspended on ropes over a gorge, scraping the lichen from vertical rock walls with long-handled tools. Rock tripe lichens are extremely slow-growing. In a study of four Umbilicaria species colonizing a Norwegian glacier foreland over 240 years, radial growth rates ranged from 0.9 to 2.4 mm per year, and individual thalli took 50 to 80 years from establishment to first reproduction. A modestly sized specimen may therefore represent decades of growth, and harvested populations cannot regenerate quickly. Yoshimura noted that iwatake had become increasingly scarce in its traditional Japanese harvesting areas by the late 20th century.
Expedition and survival use
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