ASCOMYCOTA | LECANOROMYCETES > CALICIALES > Physciaceae

Genus Physcia, meaning 'inflated, sausage-like' - from the form of the type species

Common name:            Star Rosette Lichen

Synonym:                    -

Habitat:                         Woodland, wayside trees, fences

Substrata:                     Primarily bark, but also worked timber; rarely rock and old walls

Growth form:                Corticolous, lignicolous (saxicolous)

Thallus:                  Foliose

Apothecia:                    Lecanorine

BLS identity rating:        Graded 2/5 (visual identification possible, although spot-testing recommended to be sure)

Thallus usually spherical and relatively compact, typically 2-4cm across, sometimes spreading to 6cm, but rarely more; closely appressed with radiating lobes that are more or less separate, only occasionally overlapping by a small amount; upper surface whitish pale grey, sometimes with a slightly greenish-blue tinge, indistinctly white-flecked, not pruinose, without soredia or isidia; blister-like warts or small secondary lobules sometimes at the centre of the thallus and on apothecium margins; underside whitish to pale grey or pale tan, with numerous pale to dark coloured rhizines that can protrude beyond the lobe margins.

Apothecia usually abundant, often clustered towards the centre, sessile or shortly stalked, up to 3 or 4mm dia., discs initially flat, becoming convex, normally dark brown to black, but sometimes pruinose, exciple concolourous to the thallus.

Although Physcia stellaris is not as common or widespread as Physcia aipolia, the UK distribution map is now starting to show a gradual spread south, whereas in the past it was mainly considered to be a species that you'd probably only find in the west and in Scotland. That said, it's still very much a localised species in low-pollution areas. Most records have been on branches or twigs of deciduous wayside or woodland edge trees, rather than on timber structures; rarely on rock and other hard substrates.

It can be easily confused with the much more frequent and generally larger Physcia aipolia, with which it often grows, but distinguished by its less conspicuous white flecking (best observed when moist under a x10 lens). However, reliable identification can only be confirmed through spot testing with medulla showing K-, whereas Physcia aipolia is K+.

The specimen featured here was separately identified as "very likely Physcia stellaris" by different lichenologists on the 'Lichens, Mosses, Ferns and Fungi' FB group.