Bulletin of the British Museum (Natural History)

92 BRIAN JOHN COPPINS
Saxicolous habitats
Of the 45 European species of Micarea, 21 have been found growing directly on rock (lists I,
II, and IV), although the genus is poorly represented in the main saxicolous lichen alliances of
exposed siliceous rocks (e.g. Lecideion tumidae, Rhizocarpon alpicolae, and Umbilicarion
cylindricae; list IV). As saxicoles Micarea species are more prevalent in sheltered ravines and
woodlands. In dry underhangs in rock faces, steep banks, and below overhanging trees, up to
seven species (Hst I) may be found in the ombrophobous, aerohygrophilous Micareetum
sylvicolae. The species in this community grow on rock, loose or lodged stones, exposed roots,
consolidated soil, and encroaching dry mats of bryophytes. Associated lichens from other
genera may include Coniocybe furfuracea, Enterographa hutchinsae, Melaspilea subarenacea,
Microcalicium arenarium, Opegrapha gyrocarpa, O. zonata, Porina chlorotica, P. lectissima,
Psilolechia clavulifera, and P. lucida. This community is usually well defined, but in some
situations it intergrades with other assemblages of shaded rocks such as the Lecideetum lucidae,
Coniocybetum fururaceae, Opegraphetum horistico-gyrocarpae, and the Racodietum rupestris.
A few Micarea species (list II) may be found on the upper sides of stones, boulders, and rocks
where they are subjected to direct wetting by rain, or by drips from the overlying tree canopy. In
most cases these are incidental occurrences of species more characteristic of other substrata.
However, such situations may be the normal habitat of the little known M. curvata and M.
lithinella.
In northern and western Britain several Micarea species occur on mossy rocks. The communities
involved are often difficult to place, some belonging to bryophyte-dominating syntaxa,
others to normally epiphytic communities (e.g. Parmelietum laevigatae), or to chomophytic
communities dominated by bryophytes and Cladonia species which, in turn, are often invested
by a gelatinous algal scum.
Terricolous habitats
Areas of lowland heathlands where the peaty or sandy soil has been laid bare of tall vegetation
by erosion, disturbance, or burning are colonised by several species of algae bryophytes and
lichens. The lichens involved often include species such as Lecidea icmalea, L. uliginosa, L.
oligotropha (rare in Britain), Baeomyces rufus, B. roseus, and some Cladonia spp. Micarea
species are not usually involved in such communities, although M. melaena may at times be
present, occasionally achieving local dominance. In mature Callunetum in the heathlands of
eastern England and Jylland (Denmark) M. nitschkeana is sometimes encountered in abundance
on litter, as well as on the thin attached twigs of the Calluna. Acidic soils contaminated by
heavy metals (especially lead) are often rather bare with an open vegetation, and Micarea
species (especially M. lignaria) may occur in quantity growing over moribund bryophytes and
plant debris. Soil, plant debris, and moribund bryophytes amongst coastal rocks are often
colonized by M. prasina (q.v.). M. melaenida (q.v.) is found exclusively on consohdated fine
grained (argillaceous) mineral soils. The terricolous species encountered in upland, montane, or
arctic regime are given in list V; the reader is referred to the individual species accounts for
further details.
Man-made substrata
A detailed treatment of the lichens of man-made substrata is given by Brightman & Seaward
(1977). Several Micarea species occur on worked wood (list X), but M. denigrata {q. v. ) is by far
the most successful species. M. denigrata has also been found on pieces of hardboard lying in a
dune slack at Tentsmuir in Fife. Old sackcloth and other fabrics lying on the ground in old
lead-mine workings are frequently colonised by lichens, including M. lignaria. A more surpris-
ing find was that of M. nitschkeana, growing with Scoliciosporum umbrinum, on a small plastic
carton in a heathland on the Isle of Wight. Further field studies will undoubtedly extend this list
of artificial substrata. Micarea denigrata and M. prasina are rapid colonisers of newly available
substrata, and have been collected respectively on dead culms of Cladium mariscus and
Phragmites australis in natural habitats. Both of these reeds are sometimes used as thatch, and a
close inspection of thatched roofs ought to reveal the presence of Micarea species.