| TAXON: | Protoparmeliopsis muralis (Schreb.) M. Choisy (1929) |
| RECENT SYNONYMS: | Lecanora muralis (Schreb.) Rabenh. (1845) |
| FAMILY: | Lecanoraceae |
| GROWTH FORM: | Crustose, heteromerous |
| SUBSTRATES: | Nutrient-enriched or calcareous rock; also nitrogen-polluted rock, wood, bark and a wide variety of hard artificial substrates |
| PHOTOBIONT: | Trebouxia alga |
| REPRODUCTION: | Apothecia, pyncidia |
| ASCUS: | Elongate-clavate; apex Lecanora-type; 8 spores |
| SPORES: | Ascospores ellipsoid, aseptate, 9-15(-16) × (4-)5-7 µm; conidia filamentous, sometimes curved |
| NOTABLE FEATURES: | Thallus pale yellow-green, placodioid, becoming discontinuous with age; marginal lobes sometimes long and flat, and sometimes concave with paler edges; apothecia lecanorine, abundant, crowded; discs yellow to red-brown |
| CHEMICAL TESTS: | Thallus KC+ pale yellow, Pd± yellow; UV+ dull orange (usnic acid, zeorin, ±murolic acid, ±psoromic acid) |
| HABITAT: | Wide ecological range where suitable rock is exposed; associated strongly with bird perches; agricultural and urban areas |
| DISTRIBUTION: | Common in southern and eastern England; uncommon to rare in southwestern England, Wales and Scotland |
| CONSERVATION STATUS: | Least Concern |
| LICHENICOLOUS FUNGI: | Arthonia protoparmeliopseos, Cercidospora macrospora, Spirographa sp. |
| IDENTIFICATION DIFFICULTY: | Green 2: Field identification possible with care |
| CONFUSION SPECIES: | – |
FIELD NOTES
Protoparmeliopsis muralis is unlikely to be mistaken for another lichen. At first glance, it might seem to belong to Lecanora or Myriolecis, but upon closer examination its diagnostic lobe-like edges give it away. It doesn’t merit the British Lichen Society’s lowest identification-difficulty rating perhaps only because it could be overlooked without close attention to that special feature.
It’s worth noting, though, that this feature can vary. In some cases, the lobes are long, flat and branching; in others, short, concave and edged in a paler hue. Both types of lobe are shown below. The former type is perhaps more confusing, reminiscent as it is of other placodioid lichens, such as Caloplaca sens. lat.
P. muralis is sometimes humorously called the ‘chewing-gum lichen’, and indeed it’s often found on nutrient-enriched pavement, such as around park benches. In my own experience, though, blotches of ‘chewing gum’ underfoot turn out more often to be Lecanora campestris than they do P. muralis. To me, P. muralis usually looks more like an intricate mosaic of tiny, flattened bits of putty than it does a splodge of old chewing gum.
P. muralis is nitrophilic, and it’s naturally associated with bird perches (hence muralis meaning ‘on the wall’). Tolerant of both pollution and disturbance, it fares well in modern agricultural and urban environments. There’s no doubt a ‘splodge’ of P. muralis on a pavement (or wall, kerb, tile, gravestone, bench, fence, etc) near you.
LAB NOTES
Protoparmeliopsis muralis can normally be identified without microscopy.
SPECIMENS
Protoparmeliopsis muralis : England : VC28 West Norfolk : TF8742 : October 2024 : On concrete kerb
Protoparmeliopsis muralis : England : VC27 East Norfolk : TG0743 : October 2024 : On derelict metal culvert
Protoparmeliopsis muralis : England : VC28 West Norfolk : TF9528 : October 2024 : On concrete bridge parapet
Protoparmeliopsis muralis : England : VC25 East Suffolk : TM3957 : July 2024 : On wooden bench
Protoparmeliopsis muralis : England : VC25 East Suffolk : TM3957 : July 2024 : On concrete wall
Protoparmeliopsis muralis : England : VC20 Hertfordshire : TL3510 : March 2024 : On chipseal pavement
