Physcia caesia (Hoffm.) Fürnr.
blue-headed rosette

Introduction to the Lichens


© Jim Riley     (Photo ID #12393)


E-Flora BC Static Map

Distribution of Physcia caesia unavailable

Species Information

Common Name: The Rosette Lichens. Describes the centrifugal growth form characteristic of many of the species.
Small to occasionally medium stratified foliose lichens, corticate above and below, sorediate or isidiate or not, lobes closely appressed to loosely attached, elongate-linear to elongate, averaging to 0.5–2 (–3) mm wide, thin. Upper surface usually pale whitish grey, rarely darker, K+ yellow, white-pruinose or white-spotted, dull. Lower surface pale to blackish, dull, bearing scattered, short, simple rhizines. Medulla white. Photobiont green.
Apothecia located over upper surface, disc white-pruinose to black; spores 2-celled, ellipsoid, brown, 8 per ascus.
Over acid or especially calcium-rich substrates, including rock, soil, duff, bark and bone.
Notes: Thirty species of Physcia are reported for North America and 11 of these are known to occur in B.C. Physcia has been subdivided into several segregate genera, including Phaeophyscia and Physconia.
Species description:
Lobe margins lacking cilia (Note: marginal rhizines may occur in some species, but these average to less than 0.8 mm long); lobe tips appressed AND
Thallus sorediate, isidiate or distinctly lobulate AND
Upper surface not distinctly white-pruinose; white-spotting conspicuous or not; soredia/isidia variously positioned; usually over rock (rare over bark); distribution and chemistry various AND
Lobe tips often finely sorediate, but never beaded-isidiate; distribution and chemistry various; frequent AND
Soredia located mostly over upper surface, but also occasionally in part as above; upper surface often distinctly white-spotted; medulla K+ yellow
Forms of P. caesia with soredia located primarily at the lobe tips are sometimes recognized as a separate species, P. wainioi Räsänen.
Cortex K+ yellow; medulla K+ yellow.
Atranorin and zeorin.

SourceLichens of British Columbia


If more than one illustration is available for a species (e.g., separate illustrations were provided for two subspecies) then links to the separate images will be provided below. Note that individual subspecies or varietal illustrations are not always available.

Illustration ByTrevor Goward

Habitat and Range

Habitat: Frequent over base-rich rock (rare over bark) in open to somewhat sheltered sites throughout

World Distribution: circumpolar, N to AK, S to AZ.

SourceLichens of British Columbia


Synonyms and Alternate Names:
Physcia wainioi Rasanen