Collection location: Sewanee, Franklin Co., Tennessee, USA [Click for map]
Location: 35°13’49.26"N 85°57’47.14"W, el. 575 m. Dotson Point Trail.
Substrate and habitat: Growing 2 m above the ground on the bark of a small tree under oak-dominated eastern deciduous hardwood forest at the edge of the western escarpment of the Cumberland Plateau.
Identification: This appears to be a corticolous Buelia with light grayish thallus and black apothecia, and with the apothecial rim concolorous with the disk. In the Ozarks, there are two species with these characteristics. They are identical in the field, but can be distinguished by spore characteristics (Harris and Ladd, 2005, pp.80-82):
Buellia stillingiana (“common on boles and branches of a variety of hardwoods … old fields … woodland edges … mature woodlands”)
Buellia curtisii (“occasional … often growing on upper branches of canopy trees”)
Common name: common button lichen
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This image does appear to be a buellia, but which species I am not sure. A specimen needs to be collected and keyed using microscopy and possibly chemical spot testing. Keys available include those in Brodo et al.’s Lichens of North America and Harris & Ladd (2005) Ozark Lichens.