The Graphidion

The name Graphidion is used widely by British lichenologists, sometimes to specifically refer to smooth bark communities rich in rare oceanic species. The Graphidion scriptae alliance, however, actually includes a wide range of lichen communities found on smooth bark and characterised by the dominance of crustose species. The full range of communities includes some ecologically quite separate communities. Barkman (1958) gives the faithful lichen species to the Graphidion as Graphis scripta, Pyrenula nitida (then an aggregate including Pyrenula macrospora but as the alliance is ‘typed’ on a continental stand this may actually equate to Pyrenula nitida ss), Thelotrema lepadinum, Lecanorasubfuscata” (Lecanora chlarotera?), Lecanora intumescens, Pertusaria pertusa, Pertusaria leioplaca, Pertusaria hymenea and Pertusaria flavida, that is all smooth bark communities including a lot of ordinary communities on young bark.

It is only at the association level that interesting and specialist species are faithful and many of the most interesting associations have yet to be described. James et al (1977) described the following associations:

 

Arthopyrenietum punctiformis: pioneer communities of twigs with non-lichenised black dots dominant, and including Arthonia punctiformisArthopyrenia analeptaArthopyrenia punctiformisOpegrapha atra and Tomasellia gelatinosa. There are probably further related communities to be described, particularly of sheltered twigs in woodland such as those dominated by Eopyrenula grandicula or Anisomeridium viridescens, and in hyper-oceanic woods, twigs with Arthonia excipienda, leaving the Arthpyrenietum punctiformis for more exposed ordinary twigs.

Graphidetum scriptae: communities with Graphis scripta, Graphina anguina and Phaeographis species but lacking many Pertusaria species. These are typically found in sheltered but well lit and not too wet niches. Communities in southern England appear synonymous with this, but the west of Scotland Graphidion stands are not and eastern stands are impoverished. It includes fairly uninteresting stands on fast growing young trees but old Holly and Hazel and suppressed slow growing young trees can support rich communities with uncommon or rare species such as Arthonia anglica, Arthonia astroidestera, Arthothelium ruanum, Graphina pauciloculata, Graphina ruiziana, Melaspilea lentiginosa, Mycoporum antecellens, Mycoporum lacteum, Phaeographis inusta, Phaeographis lyellii and Schismatomma niveum. Ancient woodland species shared with the hyperoceanic smooth bark communities are Arthonia ilicina and Arthonia stellaris. Sampling would probably reveal much scope for defining sub-associations, for example communities on Holly are quite distinctive.

Pyrenuletum nitidae: this is listed by James et al (1977) but is really a continental association, the tail end of which is seen on ancient Beech and Hornbeam in south east England with species such as Pyrenula nitida and Megalaria laureri present. What James et al were describing is probably a separate southern oceanic community characterised by Pyrenula chlorospila with Enterographa crassa and Pyrenula macrospora. A suitable NVC type name could be the Pyrenula chlorospila – Enterographa crassa community. It may be equivalent to the French Pyrenuletum chlorospilae Giralt. It probably has a more western distribution than the Graphidetum scriptae and replaces it in damper more shaded conditions. Gradual transitions are common. It seems to be generally a species poor community compared to the Graphidetum scriptae over much of its range and has few rare species associated with it. It is certainly abundant in numerous young and dark over grown coppices in the SW, where rare and interesting species are generally looked for on better lit trees within communities closer to the Graphidetum scriptae in composition. An exception is in the New Forest, on old Beech trees, which support Mediterranean – Atlantic species such as Enterographa elaborata and Strigula tagananae in Pyrenula chlorospila – Enterographa crassa communities. These species are also found in similar communities on old Ash trees in Ireland, so rich Pyrenula chlorospila – Enterographa crassa communities should be looked for on old Ash trees in the south west.
    

Pertusarietum amarae: shade tolerant communities on rougher bark, with Pertusaria species dominant. They are particularly characteristic of Beech and Ash, but also on less damp Oak bark. The basic community is composed of widespread species particularly Pertusaria species: Pertusaria albescens, Pertusaria amara f amara, Pertusaria flavida, Pertusaria hymenea and Pertusaria pertusa along with Phlyctis argena and Ochrolechia subviridis. This is a common community in drier areas but gets displaced by moss dominated communities in strongly oceanic areas. Within old growth stands it can be rich in old woodland species including Arthonia vinosa, Cliostomum flavidulum, Mycoporum antecellens, Phaeographis dendritica, Pertusaria multipuncta and Thelotrema lepadinum. The rare taxa include Arthonia zwackhii, Melaspilea amota, Melaspilea lentiginosa, Pertusaria amara f. pulvinata, Pertusaria pustalata, Pertusaria velata and Phaeographis lyellii.

On better lit field trees the community grades into the leafy lichen dominated Parmelietum revolutae association within the Parmelion perlatae alliance, but there are some rare specialist species centred in Pertusarietum amarae in this habitat, including Lecanora quercicola, Lecanora sublivescens and Caloplaca herbidella.

James et al (1977) mention Loxospora elatina and Schismatomma quercicola as ancient woodland species occurring in the Pertusarietum amarae but they are mainly found on more acidic bark. They are characteristic of undescribed shade tolerant crust dominated communities of strongly acid bark, probably better placed in the Parmelion laevigatae.

 

Nowhere in this is the Graphidion of hyperoceanic areas, which has yet to be formally described. James et al (1977) notes this but the taxonomy had to be sorted out first and conservation action was more urgent. A possible NVC style name could be the Pyrenula laevigataPyrenula occidentalis community. The community shares widespread species with other Graphidion communities such as Graphis scripta, Pyrenula macrospora, Graphina anguina, Pertusaria hymenea, Lecanora chlarotera and Thelotrema lepadinum. Phaeographis species are conspicuously absent with Enterographa crassa and Pyrenula chlorospila rare. Some old woodland species such as Arthonia ilicina and Mycoporum antecellens are shared with the Graphidetum scriptae. Faithful widespread species are likely to include Arthopyrenia carneobrunneola, Arthopyrenia nitescens, Bactrospora homalotropa, Mycomicrothelia confusa, Pyrenula laevigata, Pyrenula occidentalis, Thelotrema macrosporum and Thelotrema petractoides. There are numerous local species and rarities including: Arthonia cohabitans, Arthonia graphidicola, Arthonia ilicinella, Arthonia thelotrematis, Arthothelium dictyosporum, Arthothelium lirellans, Arthothelium macounii, Arthothelium orbilliferum, Eopyrenula septemseptata, Graphis alboscripta, Melaspilea atroides, Mycomicrothelia atlantica, Opegrapha brevis, Opegrapha thelotrematis, Pyrenula hibernica and more. As with the other communities there is probably much scope for subdivision; there seems to be a gradation from coastal stands with much Pyrenula macrospora to inland stands lacking this species and also specialist variants such as Pyrenula hibernica dominated stands – a lot of sampling to be done!

Beyond this the Kerry Pyrenula dermatodes stands on old Holly potentially marks a graduation towards to another more southern hyperoceanic association.

References

Barkman, J. J. (1958) Phytosociology and Ecology of Cryptogramic Epiphytes

James, P. W., Hawksworth, D. & Rose, F. (1977) Lichen communities in the British Isles: A preliminary conspectus. In: Lichen Ecology (ed. M. R. D., Seaward) 295-413.