Lichen communities in the British Isles: A preliminary conspectus

392 P. W. James, D. L. Hazphsworth and F. Rose
El>hehetum lanatae F rey
Mitt. naturf. Ges. Bern 6, 172 (1922) fas,,Ephebe lanata-Ass."l.
of algae and the bryophytes Bryu ancl
Rh m are additional important com thc
ass bryophyte cover is well develop ngia
tar y, Polychidium muscicola, enter the
I onas pide turn su ats eolentis F r ey
Mitt. naturf. Ges- Bern 6, 170 (1922) las "Jonaspis suaz,teolens-Lss."l.-Ionaspidetumodoraewirth,
Diss.Bot.,LehreL7,223(1972)fas"(tlrey 1922)iom.roo.;,1.
competition with numerous species of blue-green algae. Thelidium aeneo-
'u^inosa cited by wirth (1972) as a characteristic species in the association on
the orded from the British Isles (Durhanr).
Th n higher mountain areas ol Scotlanci,
par tains where it seldom occurs below an
altitude of 910 m. At lower altitudes the community grades into the
Aspicilietum lacustris in u'hich Placynthium pannariellum and. polyblastia
cruenta, at least above 200 m, may also be present as subsidiary species.
Verrucarietum siliceae Wirth & Ullrich
lz Wirth, Diss. Bot., Lehre 17,219 (1972)-
This association, the verrucariehtm siliceae, comprises communities
growing on siliccous rocks in streams and lakes where therc is a moderate
10. Lichen Communities in the British Isles 393
to rapid water flow, sufficient light and lack of mud and silt. Although the
association is frequently submerged throughout the year it may also bc
found in shaded strcam beds which dry out for relatively short periods of
the year. Verrucaria aquatilis, V. hernstochii and V. silicea are characteristic
of the Verrucarietum siliceae. According to Wirth (1972), V. silicea is the
siliceous rock morphotype of V. elaeomelaena which occurs in similar
situations on submerged limestones. \iarious free-living algae of u'hich
Hildenbrandtia and Lemanea merit particular mention are often present
as is the moss Fontinalis antipyretica. The rcre Collema fluoiatile is
faithful to the association in Britain.
A nodum characterizedby Bacidia inundata, Staurothele fissa, Verrucaria
latebrosa and V. margacea, not uncommon in western areas of the British
Isles, is also referred to the Verrucarietum siliceae. This may be identical to
the V erruc arietum laeo ato- funudatae W irth.
VII. Terricolous Communities
In gcneral, terricolous lichens present much greater problems of phytosociological
delimitation than communities characteristic of other substrates,
because lichens on soil usually form an intimate and integral part
of alrcady designated higher plant associations; they do not form the more
or less exclusive stands seen in the case of most corticolous and saxicolous
lichen communities. In the case of terricolous communities, lichenologists
have often adopted classificatory schemes which pay only minor attention
to the vascular plants involved (e.g. Klement, 1955). While this approach
can be sympathized with, as those describing higher plant syntaxa have all
too frequently ignored lichens in their surveys, in our vierv an entirely
acceptable system for terricolous communities must take a proper account
of both phanerogam and cryptogam components.
An outline of the higher plant syntaxa which may be recognized in
Britain is included in Shirnwell (1971). Those present in Britain as a u'hole
were summarized by Tansley (1939) although he did not adopt the nomenclatural
system used by continental workers, and those in Scotland are
reviewed in some detail in the work edited by Burnett (196+). A survey of
the plant associations of lowland Britain is currently in progress but results
from it will not be generally available for some time.
For simplicity, we have separated the terricolous lichen communities into
the following four categories, those of pebbles, basic soils, coastal soils
and acid soils or peat.