Lichen communities in the British Isles: A preliminary conspectus

314 P. W. James, D. L. Hawkszoorth and F. Rose
dry dccorticate wood C. coniocraea rnay be almost entirely replaced by
C. parasitica, and in damp woods i'the south and south-west, the rather
rare c. caespiticia also cntcrs into the association. The most pollutiontolerant
facies of this community, however, merely compriscs swards of
c. coniocraea andlor c. macilenta. The association intergrades with othcr
noda containing species such as Lecidea granrtlosa, L. uliginosa, Micar.ea
prasirttt, Peltigera canina, P. polydactyla, P. praetextata and Sphaerophonts
globosus. Bryophytes are important components in this community, the
introduced Orthodontium lineare (see Rose and Wallace, 1974) bcing
particularly characteristic in the south-eastern and Midland counties. In
relatively rrnpolluted areas (lsnea-rich facies occur in better lit sites but
these, follorving Barkman (1958), are placed in the Cladonieto (.isneettLm
tnberculatae here (see p. 338).
The Cladonietum coniocraeae has been treated as a synonym of the
Cladonietum cenoteae by a number of lichen phytosociologists (e.g.
Wilmanns, 1966) follorving Klement (1955), but this vierv was rejectecl
for the llritish Isles by Hawksworth (1972a);from the information provided
above it will be evident that these two associations differ fundamentally
in species composition, habitat and distribution and thus clearlv
merit treatment as distinct associations.
\rarious infrassociational taxa have been described vvithin this association
(..g. var. macrocladonietum digitatae Duvign., yar. microcla.donietrnrt
coniocraeae Duvign., var. sphaerophoretum globosae Duvign., subass.
cladonietum digitatae Klem.) and while most can be recognized within thc
Ilritish Isles they appear to be of minor synsystematic value.
All. 3. Graphidion scriptae
Gral>ht)dion scriptae Ochsn., Jahrb. St. Gall. naturw. Ges.63,49 (1928); type:
Pyrenuletum nitidae Htl.-Graphidioz Almb., K. svensha VetenshAhad. Azth.
natursk. 11, 21 (1955); type: Nitidetum Llmb.
This particularly r,vell marked alliance is characteristic of smooth bark,
usually on young trees, branches or twigs, and comprises two distinct
elements, (1) the pioneer community of trees, and (2) some communities
persisting on mature trees lvith smooth bark or restricted to deep shade.
The ()rapltidion scrilttae is characterized by a wide range of crustose
specics and where macrolichens are encountered within its associations
they can be viewed as pioneers of subsequent successional stages. Most of
the crustose species involved are esorediate with either lirellate or pyrenocarpous
ascocarps.
The alliance is entirely restricted to the bark of deciduous trees in the
Btitish Isles. While it evidently merits subdivision into several associations,
10. Lichen Comnnnities in tlte British Isles 31--c
few studies have been made on this alliance in llritain so far and the
following treatment is conseyrenia fallax, A. punctiformis, Dermatina quercus
(second or third year oak twigs), O1>egrapha atra, Stenocybe pullatula
(confined to Alnus tv,'igs) and Tomasellia gelatinosa (mainly on Corylus).
The age of the trvigs and the degrecs of preliminarl' scarring influence the
intrusion of additional hypophloeodal species which first appear arottncl
leaf and girdle scars. Lecanora carpinea, L. chla.rotera, L. cottJusa, Lecidea
symmicta, Lecidella elaeochrome and Rinodin.a sophodes indicate transitions