Phaeophyscia orbicularis

Family: Physciaceae

Brown Rosette Lichen (Phaeophyscia orbicularis) is a small, gray-brown foliose lichen that forms tight rosettes on tree bark and other substrates. Though modest in size, it is widespread and reliable, often appearing as part of mixed bark-lichen communities where subtle color and texture differences reward close inspection.

For representative images and visual context, see the Mealy Shadow Lichen in the Gallery section.

Description

Phaeophyscia orbicularis is recognized by:

Growth form: foliose
Thallus: gray-brown to olive-brown, thin, closely appressed
Lobes: narrow, short, rounded to slightly elongate, often overlapping
Surface features: fine soredia common along lobe margins and surface
Underside: pale to dark brown, with simple rhizines
Attachment: firmly attached to substrate

Colonies typically form compact rosettes, though adjacent individuals may merge into irregular patches on suitable bark.

Substrate and Habitat

Typical substrates and settings include:

Bark of deciduous trees (frequently hardwoods)
Occasionally on wood or rock in urban and disturbed areas

Notes may include:

Tolerance of open light to partial shade
Frequent occurrence in nitrogen-enriched environments
Often growing intermixed with other small foliose lichens

Identification

Key features for field diagnosis:

Color: gray-brown to olive-brown
Form: small, tight foliose rosettes
Surface: dull, often lightly pruinose, with granular soredia
Underside: brown with evident rhizines
Reproductive structures: apothecia may be present but are not always conspicuous
Chemistry: typically K−

Commonly confused species include:

Physcia species (usually with black undersides and different attachment)
Other Phaeophyscia species, which may require underside and soralia details for separation

Consistency across multiple observations—particularly underside color and attachment—helps confirm identification.

Ecology and Notes

Phaeophyscia orbicularis is a nitrophilous species, frequently associated with nutrient-rich or disturbed environments. Its presence is common in urban, suburban, and agricultural landscapes, where it contributes to diverse bark-lichen assemblages.

In Minnesota, it is widespread and regularly reaches Research Grade on iNaturalist, reflecting both its abundance and relative ease of confirmation with clear photographs.

References

Consortium of Lichen Herbaria
https://lichenportal.org/
Minnesota Lichen Guide
https://www.minnesotalichens.org/
iNaturalist taxon page
https://www.inaturalist.org/taxa/Phaeophyscia-orbicularis