Rock tripe (Umbilicaria mammulata) is an edible lichen. There are 65 species of rock tripe, found in rocky or mountainous environments worldwide, especially where other organisms are scarce. The common rock tripe grows on shaded rocks in the forests of eastern North America.
Lichens are complex life forms that comprise at least two separate organisms, primarily a fungus and a photosynthesizing organism or “photobiont,” either an alga or cyanobacterium. They are able to live in a wide range of environments, including some of the most hostile on the planet such as the arctic tundra and hot, sandy deserts.
The symbiotic nature of lichens was discovered in 1867 by the Swiss botanist Simon Schwendener. Since that time, and especially with the advent of new molecular technologies, research has shown that the nature of the symbiosis is far from the simple picture of one algal species in partnership with a single fungus.
Common Rock Tripe. Credit: Andrew Khitsun, Mushroom Observer. CC BY 3.0
The genus name Umbilicaria refers to the lichen’s single attachment point in the middle, like a navel. The species name mammulata, literally means "small breasted" but is more accurately translated as "bumpy," describing the papillae or bumps on the black lower side of the lichen. The name of the lichen is usually the same as that of its unique fungus, but the algae have their own species names as some can be part of more than one lichen. The algal partner in Umbilicaria is from the genus Trebouxia, which is a common partner in many lichen species.
The common name, rock tripe, relates to their habitat of rocky surfaces and their resemblance to the food stuff "tripe," which is eaten around the world. Some lichens have common names that include the word “moss” for example "reindeer moss," as they may superficially resemble and grow with mosses. However, mosses are a different group of organisms that are not closely related to lichens.
A lichen is not a simple plant or fungus but a partnership of at least two organisms growing together. Lichens combine a fungus and a “photobiont,” either algae or cyanobacteria, which together form a new organism such as the rock tripe lichen. While ordinary fungi get nutrition by decomposing dead organic material, such as rotting wood, the fungi in lichens are fed by the carbohydrates produced by their photobiont. “Lichens are fungi that have discovered agriculture,” according to lichenologist Trevor Goward.
Recent research has shown that lichen symbiosis is not as clear-cut as it first seemed. For example, the same lichen species can involve different algal partners depending on its geographic location. Recently scientists have discovered a third partner in many lichen species: single-celled basidiomycete yeasts embedded in the lichen’s cortex ("skin"). This other species most likely produces chemicals that help lichens ward off predators and repel microbes.
Did you know? Many (but not all) lichens are very sensitive to air quality as they have no roots and very efficiently absorb elements from the air. Lichens have been used to monitor air quality since the late nineteenth century when the increase in industrial pollutants, particularly sulphur dioxide, led to the decline of lichens around urban areas.
Food is the primary human use for rock tripe lichens, although some species are also used for fabric dye. However, rock tripe and other lichens are not to be considered an agricultural product. Because they grow very slowly, they are not commercially farmed, but rather are “foraged” from the wild.
In North America, rock tripe lichens are viewed as an emergency survival food, but in other countries they are viewed as a delicacy. “Tripe” is the culinary name for a ruminant’s stomach (typically beef), and is usually cooked by boiling for several hours. George Washington’s troops were said to have gathered and boiled rock tripe for soup at Valley Forge, Pennsylvania, during the winter of 1777–78.
The common name in French is tripe-de-roche, the exact translation of the English. It was eaten as survival food by French Canadian settlers and traditionally boiled in soups by the Cree and other Native Canadians. In Japan, rock tripe (Umbilicaria esculenta) is called iwa-take, or "rock mushroom." They are harvested by foragers then either deep-fried or added to salads.
Did you know?
Beatrix Potter (1866-1943). Credit: Wikimedia Commons. Public Domain
|The author Beatrix Potter (1866–1943) was also a naturalist who was particularly interested in fungi and lichens. She was one of the first to recognize the lichen’s symbiotic nature. Although it was never published, her paper on fungi “On the Germination of the Spores of Agaricineae” was presented to the Linnean Society in London in 1897. Because the Linnean Society did not admit women to meetings at that time, it was read on her behalf by George Massee, a mycologist at the Royal Botanic Gardens at Kew.|
Detailed information on lichens, written for hikers on the Hiker’s Notebook website
Podcasts from the Encyclopedia of Life (EOL), produced by Atlantic Public Media and funded by the Museum of Comparative Zoology at Harvard University.