Is Stirtonia alba in North America? Resolving a nomenclatural impasse and assessing the taxonomic status of the Arthonia alba complex

Abstract The invalid combination Stirtonia alba (Mull. Arg.) ined., based on Arthonia alba Mull. Arg., is listed for the continental United States in several important online repositories, including CNALH, USDA PLANTS and EOL. Although Arthonia alba belongs in Stirtonia, the name cannot be used in that combination, as it is blocked by S. alba Groenh. ex Makhija & Patw., a species described from Java, Indonesia, and both taxa are distinct morphologically, anatomically and chemically. Here, we resolve this nomenclatural impasse by proposing the new name S. caribaea for A. alba. We examined further material identified as “A. alba / S. alba” from North America and the Caribbean. Specimens ascribed to “S. alba (Mull. Arg.) ined.” from North America (Louisiana, Florida) were found to be misidentifications in other genera, with only one collection confirmed as a Stirtonia. This specimen was determined to be S. punctiformis, and is here reported as new to North America, representing a northward range extension fr...