World distribution: Endemic to South Norway
Ecology: Results. The substrate (indicated in 18 localities) included Betula pubescens (14), Picea abies (2), Juniperus communis (1), Pinus sylvestris (1), and Sorbus aucuparia (1). The habitat (indicated at 14 localities) included northern boreal birch forest (8), northern boreal mixed birch/spruce forest (1), middle boreal birch forest (1), pine forest (1), mire (1), 'by a lake' (1), and scree (1). Discussion. Nordnes (1982b, 1983; see notes below) gave special attention to P. esorediata in his study of the lichen flora in Setesdalen. It is most common in northern boreal birch forests, but also occurs on solitary trees above timberline. At lower altitudes the species was most common on Betula pubescens in mires and by lake shores. A characteristic substrate was smooth bark on old or dead parts of small deformed birch trees near the timberline (Nordnes 1982b, 1983)
Threats: Results. Recorded threats were land development (building of cottages) in one locality (1929)
Status: Only 2 of the old localities were investigated; the species was present in both. Three new localities were discovered. Most collections are from the early 1980's, when the species was actively searched for. In Setesdalen, the species was characterized by Degelius (1956, translated) as 'not rare within a limited area' and by Nordnes (1983, translated) as 'very common at Valle and Bykle'. No localities are protected
Notes: Nordnes (1983) found the species in 16 localities in Setesdalen, but only eight of these are represented by material in O and included in this treatment; the precise localizations of the other eight localities are unknown, but they were certainly close to those filed in O. The identity of the material from Oppland (1927) is doubtful since the herbarium material is rather poor. It may represent fruiting specimens of P. hyperopta. Poelt (1970) considered P. esorediata to be the primary taxon of P. hyperopta. The postglacial history makes it more likely that P. esorediata originated by a mutation in P. hyperopta which affected its capacity for producing soralia (Nordnes 1982b)..
Specimens in other herbaria, litterature, etc.