When: 2015-07-03

Collection location: Atascadero, California, USA [Click for map]

35.4625°N 120.6761°W 277m [Click for map]

Who: J-Dar

Specimen available

Occurs on a large sandstone boulder outcrop in sycamore-oak riparian habitat of Atascadero Creek on the side of Highway 41 West.

Thallus white, 5cm diameter, with some crystals on lobes, especially tips, no hairs on lobe margins, lobe margin up to 2.5mm, but usually smaller, K+Y, medulla white, K-, lower side white with whitish to dark simple rhizines. No soredia or isidia present, apothecia 1-2(4)mm, disc black with distinct white pruina.

In the Nash key, you need to accept that the pruina on the lobes constitutes “crystals”. It seems light on this specimen, but if you go the other way you end up at Physcia halei, which does not have pruina on the apothecia disc, among other minor differences.


K- medulla, K+ thallus upper cortex
Medulla K- despite sloppy application showing K+Y reaction from upper thallus cortex
Note crystal-like pruina on upper lobe surface
Note pruina on apothecia disc

Proposed Names

92% (2)
Used references: Nash Sonoran Flora
Based on microscopic features: crystal-like pruina on lobe tips
Based on chemical features: Medulla K-

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= Observer’s choice
= Current consensus


Add Comment
Great, thanks!
By: J-Dar
2015-07-08 20:08:43 PDT (-0700)

Crystals were much more distinct on a recent observation of P. biziana on oak bark, so this one I had to make sure I understood if it fit within the “crystal” definition. I think I got my bearings now…

P. hale is a much narrower-lobed species
By: Jason Hollinger (jason)
2015-07-08 19:08:38 PDT (-0700)

This looks just right to me for P. biziana. Moberg’s “crystals”, as you see, require some experience to interpret! :)