Lichen communities in the British Isles: A preliminary conspectus

376 P. W. James, D. L. Hawhsworth and F. Rose
The association is often rich in bryophytes of which Andraea rothii,
A. rupestris (syn. l. petrophila), C),nodontium polycarpum (rare), Hypnunt
cupressiforme, Isothecium tnyosuroides, Orthotrichum anomalum, Rhacomitriurnfasciculare
and R. heterostichumrnay be considered as characteristic"
The Parmelietum omphalodrs occurs at lower altitudes and latitudes than
the Umbilicarietum cylindricae often occurring even in or near coastal
areas in western parts of the British Isles. At higher altitudes it tends to
grade into the Umbilicarietum cylindricae and species such as Cornicularict
normoerica, Rhizocarpon lecanorinum, R. polycarpon, Sphaerophorut
tragilis, Umbilicaria polyphylla and U. polyrrhiza become more abundant"
As a rule the Parmelietum omphalodzs prefers more sheltered sites than the
(J mbilic ar i e tum c y lindr i c ae.
Klement (1955) treated Du Rietz's name Parntelion omphaloclis as a
synonym of the (Imbilicarion cylindt icae reserving a homonym of the
latter name for a different, more upland, community including, for
example, Hl,pogymnia intestiniformes. The usage adopted herc follows that
of Wirth (1972).
(lmbilic ariet am cylindric ae (Frey) Frey
Ber. Geobot. Inst. Rilbel 1932, +0 (1933). Gyrophoretum cylindricae Frey, Mitt.
naturf. Ges. Bern 6, 168 (1922) las "Gyrophora cylindrica-Ass."l.-Umbili-
carietum deustae Frey, Ber. Geobot. Init. Riibel 1932,49 (1933).
The Umbilicarieh,tm cylindricae is a more upland and more light-demanding
counterpart of the Parmelietum omphalodis characterized by species typical
of the alliance (p.374). Both associations may occur in very close proximity
to one another and the relative abundance of the characteristic species may
vary considerably in different sites depending on both geographical
location and altitude (particularly as its important components are limited
climaticallv in the British Isles). T'his association is optimally developed
on the uppermost slopes of mountains in the Scottish Highlands where it
represents a seral stage leading to the Rhizocarpetum alpicolae, an association
with a very limited distribution in the British Isles.
The synsystematics of the Llmbilicarietum cylindricae are poorly understood
in Britain but our observations suggest that they are very complex.
Preliminary studies indicate that there are sevcral distinctive noda (indicated
below), some of which may be referable to the Parmelietum omphalodis,
and others of which may well prove to merit recognition as separate
associations when thoroughly investigated.
1. I)ominatedby Fuscidea tenebrica with F. cyathoid,es and Rhizocarpon
geogra\hicum ^s
?rp.."a mounta
I,ake District an
^-
2. A shadY a
10. Lichen Communities in the British Isles 377
k.ro*n in Britain only from Scotland
acid, nutrient-Poor rock'
c of sunnY rocks in
rlY abunclant in the
Fuscidea toenlaYum'
and al"vays found on
*-1.' oo-itrated by Fuscidea cyathoides but including Lecidea leucophaea,
L. lithoph.ita, L. pantheTina, Pertusaria corallina and Rhizocarpon ge}-
/rat;ri* ugg.. (oft".r R. riparium) as characteristic associates. This
'rroarr- tends to occur at lower altitudes and latitudes than the preccding
i*o .roau and is particularly well developed in the Southern Pennines and
peak District on;illstone grit rocks. This nodum is close to the Parmelietum
omphalodisbut is placed heie tentatively as it sometimes includes LlmltiLicaria
polyphylta, U. polyrrhiza or (J. torrefacta.
' +: ifacies on mineral-rich rocks often in rathcr moist situations as in
shallow valleys or near mountain lakes dominated by Lecidea lithophilabt
including L.iapicida and. L. leucophaea; Alectoria nig icans and Cornicularia
aculeata arc fiequent associates on mosses in such communities. This
facies has a cleai affinity with the Acarosporetum sinopit:ae (p. 383) but is
poor in species restricted to mineral-rich sites while including many
mineral-tolerant ones'
5. A sun-loving markeclly wesrern community particularly well developed
in the Rhinog mountains in wales dominated by Lecanora mauroides and
Rhizocarpon geographiatm but including Lecidea pantlterina and L.
tenebrosa at high frcqtrencies'
6. The Umbilicar'ia deusta-dominated nodum treatcd as a distinct
association by many authors (the (lmbilicarietum deustae lirey, see above)
which is well developed by the sides of upland mountain streams.
7. The very high altitude (lmbilicaria hyperborea nodum'
8. The Umbitiiaria crustulosa-dominated nocr,um of almost vertical
south-facing, hard volcanic rocks found on the Langdale Pikes in the Lake
District (see Brightman, L962' for lists of associatcs)
The ,,typical'l Llmbilirarietum cylindricae is taken here to include high
fr.qt,,"..i". of Llmbiticaria cylindrica, (l' polyphylla, (l' p,ol1n'rhiza' LI'
proioscidea ancl/or LI . totre.facta. 'Ihis nodum has a particular prcference
?or well lit rather course-giained rocks in mountainous areas (particularly
granite) with Cornicularii normoerica, PserLdephebe pultescenr and the other
tacrolich".rs mentioned as characteristic of the alliance on p.374 occurring
in it. Associated bryophytes include Andraea rupestris, Grimmia doniana,
G. trichophylla, Gymnctmilrioz spp., Hedztigia ciliata, Ptychomitriun
polyphyllttmi Rhoromit",hLm fasciculaye and R. heterosticlntm var. heterostichum.