''Physcia millegrana'', commonly known as the mealy rosette lichen, is a species of

corticolous This glossary of mycology is a list of definitions of terms and concepts relevant to mycology, the study of fungi. Terms in common with other fields, if repeated here, generally focus on their mycology-specific meaning. Related terms can be found ...

(bark-dwelling),

foliose lichen A foliose lichen is a lichen with flat, leaf-like , which are generally not firmly bonded to the substrate on which it grows. It is one of the three most common growth forms of lichens. It typically has distinct upper and lower surfaces, each o ...

in the family

Physciaceae The Physciaceae are a family of mostly lichen-forming fungi belonging to the class Lecanoromycetes in the division Ascomycota. A 2016 estimate placed 19 genera and 601 species in the family. Description The Physiaceae family includes various ...

. It is common in the eastern United States. It was

formally described A species description is a formal scientific description of a newly encountered species, typically articulated through a scientific publication. Its purpose is to provide a clear description of a new species of organism and explain how it differ ...

as a new species in 1940 by the lichenologist

Gunnar Degelius Gunnar Bror Fritiof Degelius (né Nilsson until 1932; 27 January 1903 – 22 July 1993) was a Swedish lichenologist. Between the publications of his first and final scientific papers, Degelius had a 70-year-long research career. While he was b ...

. This gray lichen with a pale underside is characterized by its coarse

soredia Soredia are common reproduction, reproductive structures of lichens. Lichens asexual reproduction, reproduce asexually by employing simple fragmentation and production of soredia and isidia. Soredia are powdery propagules composed of fungus, fung ...

(granular vegetative

propagule In biology, a propagule is any material that functions in propagating an organism to the next stage in its life cycle, such as by dispersal. The propagule is usually distinct in form from the parent organism. Propagules are produced by organisms ...

s) that are densely distributed the margins of , giving them a somewhat ruffled appearance.

Secondary metabolite Secondary metabolites, also called ''specialised metabolites'', ''secondary products'', or ''natural products'', are organic compounds produced by any lifeform, e.g. bacteria, archaea, fungi, animals, or plants, which are not directly involved ...

s (

lichen product Lichen products, also known as lichen substances, are organic compounds produced by a lichen. Specifically, they are secondary metabolites. Lichen products are represented in several different chemical classes, including terpenoids, orcinol deri ...

s) found in ''Physcia millegrana'' include atraric acid, methyl 3-hydroxy orsellinate, and divaricatic acid.

References

millegrana Lichen species Lichens described in 1940 Lichens of the United States Taxa named by Gunnar Degelius {{Caliciales-stub