Lichen communities in the British Isles: A preliminary conspectus

340 P. W. James, D. L. Hawhsworth and F. Rose
Although this association has generally been placed in the Xattthorion
we suspect that it may be more closely allied to the (Jsneion as it parallels
the (Jsneetum articulato-foridae b:ut is found in somewhat more nutrientrich
sites. Some tendency to intergrade with the Llsneetum sultfloridanae
also supports its positioning here.
U sne etum artic ulato-floridae v ar. c er atinae D. Hawksr.r'.
Fld stud.3,5+3 (1972).
This often spectacular community (Fig. 6), which characteristically occurs
in very well lit situations and is optimally developed on the uppermost
sloping or horizontal boughs of trees, has a markedly southern and southwestern
distribution in the British Isles. The most important species of
the variant are Usnea articulata, U. ceratina, U. florida and U. rubiginea,
although U. inflata (syn. U. intexta) and U. subfloridana are often also
present.
In the southern counties of England a facies dominated by U. cet,atinu
and U. inflata occurs not uncommonly on almost vertical lvell lit trunks of
Fagus and Quercus in glades; U. articulata is generally absent in this
facies although U. rubiginea is often present. This nodum may in future
merit separation as a distinct association.
The "typical" variant of this association, as interpreted by Barkman
(1958), is still present in Brittany and includes Heterodermia leucomelos,
Pseudocyphellaria aurata and Teloschistes flaaicans. These species are now
very rare in Britain, perhaps prefer more nutrient-rich barks, and seem
better placed in a separate association, the Teloschistetum flavicantis (p.
348), which is always poor in (Jsnea species. The relationships between
this community and both the Usneetum forido-neglectae Bibinger and the
Llsneetum rubicundae Barkm., both unrecognized in Britain, merit further
study.
Usneetum filipendulae ass. nov. prov.
This poorly understood association, which is not validated here in the
absence of detailed records, is characteristic of ancient coniferous forests
in Scotland and dominated by Usnea filipendula and U. fbrillosa. Alectoria.
sarmentosa, Bryoria capillaris, and sometimes (J. hirta, may be further
important components of this association. It should be noted that this
commr,rnity may perhaps be in reality a species-poor variant of the central
and northern European montane (Jsneetum barbatae Ochsn. (for which the
later name Letharietum dioaricatae Frey was employed, perhaps unnecessarily,
by Barkman, 1958),
Frc. 6. (Jsneetum articulato-floridae var. ceyatinae on salix in marsh' species
present include Eaernia prunastri, Hypogymnia pl'4tsodes, Parmelia perlata, P.
sulcata afld (Jsnea ceratina (s. Devon: slapton, Duck Marsh, 1975, F. S. Dobson).