Nephroma helveticum was first
described by the Swedish lichenologist
Erik Acharius in 1810. The
species epithet alludes to its
type locality, Switzerland. The species is part of a complex taxonomic group that includes
N. tropicum, with which it has historically been confused. Modern
molecular phylogenetics studies have shown that material previously identified as
N. helveticum actually comprises two distinct species. Early
molecular phylogenetics studies in the early 2000s provided the first evidence that
N. helveticum likely represented a complex of closely related taxa. Lohtander and colleagues (2002) found high genetic variability in both nuclear and mitochondrial DNA regions that corresponded with morphological and chemical variation, suggesting the presence of multiple distinct species within what was then considered
N. helveticum sensu lato. Their work also established the placement of
N. helveticum within one of four major clades in the genus
Nephroma. The application of the name
N. helveticum remains somewhat uncertain, as the
type specimen from Switzerland has never been found again in that country, leading some researchers to speculate that the original material may have been mislabelled. The
lectotype specimen is held in the Acharius Herbarium (H-ACH 14703B), housed at the Botanical Museum of the
Finnish Museum of Natural History. Molecular analysis of
ITS and
mtSSU DNA regions has revealed two major
clades within what was traditionally considered
N. helveticum. One clade corresponds to
N. helveticum sensu stricto (in the strict sense), while the other represents
N. tropicum. The species can be distinguished by subtle
morphological differences and chemical composition, though there is some overlap in characteristics. Several other species names have been historically associated with this complex, including
N. subhelveticum (now considered a
synonym of
N. helveticum) and
N. sipeanum (now considered a synonym of
N. tropicum). In total, about 20 different species names have been applied to members of this complex since its first description. In Nordic countries, where the species complex has been extensively studied,
N. helveticum sensu stricto is known from approximately 20 localities across Finland, Norway and Sweden, while
N. tropicum is known from just a single Norwegian location. These are extremely rare species in the Nordic region, with both being classified as
critically endangered (CR) in Norway. In Sweden,
N. helveticum is listed as
data deficient (DD), reflecting uncertainty about its conservation status. In North America, the species is commonly known as the "fringed kidney lichen". ==Habitat and distribution==