Umbilicaria torrefacta (Lightf.) Schrader
Punctured Rock Tripe Lichen
Basis for Listing
Umbilicaria torrefacta is a boreal lichen species with a mainly northern and western distribution. It is found from Alaska south to California, and east to the Lake Superior region and the high mountains of New England. In Minnesota, U. torrefacta is known from a single population documented in Cook County in 1980. At the time of its designation as a state special concern species in 1984, its distribution in the state was uncertain and the known locality was not threatened. However, further searches have not yielded any new locations in the state, and the single known population in is being subjected to increased rock-climbing activity. For these reasons, U. torrefacta was subsequently reclassified as state endangered in 1996.
Umbilicaria torrefacta is a foliose (leaflike) lichen. The thallus (lichen body) is olive green to brown, with deep cracks in the upper surface. The upper surface often appears to be cut or eroded near the margins, sometimes becoming actual holes in the thallus tissue. The center part of the thallus is smooth and fairly thick. Apothecia (disk-like sexual reproductive structures) are common on the upper surface of this lichen, usually being closely appressed to the thallus. Like other Umbilicaria, this species attaches to the substrate at a single point. The lower surface of the thallus is brown, with plates near the center attachment point and rhizines (rootlike structures) near the margins. When subjected to chemical spot tests, this lichen does not react to potassium hydroxide, but it does turn red when exposed to bleach (Wetmore 1981).
Like all species of Umbilicaria, this lichen grows on bare, sunny exposed rocks, usually on nearly-vertical faces on rocky ridges. In Minnesota, U. torrefacta is found on a rocky ridge that extends into Lake Superior.
Biology / Life History
Umbilicaria torrefacta reproduces sexually through the dispersal of spores. Wind and rain are the likely agents for dispersing this lichen's spores.
Conservation / Management
The preferred rock outcrop habitat for this lichen is also attractive to rock climbers, who are drawn by the physical challenge. Consequently, recreational use of the rock faces that harbor this rare lichen presents a serious threat to the only known population in the state.
Conservation Efforts in Minnesota
This species and other rare lichens are targeted for botanical searches by scientists in an attempt to locate additional occurrences and conserve remaining populations.
References and Additional Information
Brodo, I. M., S. D. Sharnoff, and S. Sharnoff. 2001. Lichens of North America. Yale University Press, New Haven, Connecticut. 795 pp.
NPLichen, A Database of Lichens in the U. S. National Parks [web application]. 2008. Version 4.5. U. S. Geological Survey.
Wetmore, C. M. 1981 (revised 2005). Keys to the Lichens of Minnesota. Department of Plant Biology, University of Minnesota, St. Paul, Minnesota. 92 pp.