| TAXON: | Polycauliona polycarpa (Hoffm.) Frödén, Arup & Søchting (2013) |
| RECENT SYNONYMS: | Xanthoria polycarpa (Hoffm.) Th. Fr. ex Rieber (1891) |
| FAMILY: | Teloschistaceae |
| GROWTH FORM: | Foliose, heteromerous |
| SUBSTRATES: | Bark of well-lit twigs and branches of broadleaf shrubs and trees; also nitrogen-polluted bark, wood or rock |
| PHOTOBIONT: | Trebouxioid alga |
| REPRODUCTION: | Apothecia, pycnidia |
| ASCUS: | Elongate-clavate; apex Teloschistes-type; 8 spores |
| SPORES: | Ascospores ellipsoidal, polarilocular, 11-15 × 6-8 µm; conidia ellipsoidal |
| NOTABLE FEATURES: | Thallus yellow-orange, small, neat, typically subfruticose or cushiony; lobes plump, divided; apothecia lecanorine, copious, often obscuring lobes; discs orange |
| CHEMICAL TESTS: | Thallus K+ crimson-purple, UV+ red (parietin, minor amounts of other lichen substances) |
| HABITAT: | Scrub, open woodland and parkland featuring broadleaf shrubs or trees; increasing in agricultural and urban areas |
| DISTRIBUTION: | Widespread and common across Britain |
| CONSERVATION STATUS: | Least Concern |
| LICHENICOLOUS FUNGI: | Erythricium aurantiacum, Illosporiopsis cf. christiansenii, Lichenoconium erodens, Lichenoconium xanthoriae, Marchandiomyces corallinus, Spirographa sp. |
| IDENTIFICATION DIFFICULTY: | Green 1: Field identification possible |
| CONFUSION SPECIES: | Xanthoria parietina |
FIELD NOTES
Polycauliona polycarpa is a highly distinctive corticolous lichen that tends to form neat, cushiony yellow rosettes nearly smothered in abundant yellow-orange apothecia. It can be overlooked because of its small size, but also because it superficially resembles young Xanthoria parietina, whose general habit it shares. And since X. parietina is one of the most common lichens in Britain, it’s easy to assume that any foliose, yellow lichen that you see must be that most ‘inevitable’ of species.
Yet if you avoid that assumption, it’s easy to distinguish the two. X. parietina forms large and expansive thalli, and even young specimens show distinctive wide, flat, skirt-like lobes. By contrast, mature P. polycarpa remains small and compact, and its plump, divided lobes can be hard to spot for the many crowded apothecia. And though both lichens tend to prefer well-lit situations, P. polycarpa seems particularly to thrive in the ‘nooks’ where twigs branch, perhaps because it competes less well on open surfaces than loose and spreading X. parietina.
Like X. parietina, though, P. polycarpa is nitrophilic. It has increased its range especially in agricultural and urban areas, where surfaces are impregnated with ammonia and nitrogen oxides. In these areas, P. polycarpa can be found on worked wood and on stone as well as on bark. It’s a common lichen in its own right, and it’s worth looking for it where X. parietina also grows.
LAB NOTES
Polycauliona polycarpa can normally be identified without microscopy.
SPECIMENS
Polycauliona polycarpa : England : VC25 East Suffolk : TM3957 : August 2024 : On wooden rail
