[5] The main morphological characteristics of the lichen include its blue-grey thallus, Trentepohlia algal photobiont partner, and white sporodochia.

Additional populations are scattered throughout the Ozarks and Piedmont regions of the southeastern United States, with disjunct occurrences in Minnesota and a single known site in Ontario, Canada.

In rarer instances, S. americanum can be observed on non-calcareous rock overhangs in high-humidity environments, often associated with talus slopes or water bodies.

This rare lichen, found primarily in isolated pockets of mature forests in eastern North America, has experienced significant historical decline due to widespread logging and land-use changes.

Because of the pressures on its localized populations, increasingly fragmented habitat, and the lack of any planned protection actions, it was assessed as an endangered species for the IUCN Red List in 2021.