THE LICHEN FLORA OF THE BASILDON AREA 151
Peltigera spuria (Ach.) DC.
Scarce on well-drained soil. 51/69.
Soil-covered clinker railway embankment, Hutton (1971, PME-B);
garden lawn, Norsey Road, Billericay (1974, IMH).
Physcia adscendens (Th. Fr.) Oliv. em. Bitt.
Frequent on limestone and mortar; rare on sandstone and Salix. 51/68,
69, 79.
Limestone headstones and wall of All Saints' Church, Hutton (1972,
PME-B); limestone and sandstone gravestones, St Mary's Church, Little
Burstead (1973, IMH); limestone gravestone, Congregational Church,
Billericay (1974, PME-B); mortar of church wall and limestone grave-
stones, St Mary's Runwell (1974, PME-B); single specimen on old Salix
stump, Westley Heights, Langdon Hills (1974, PME-B).
P. caesia (Hoffm.) Hampe
Common on limestone, asbestos-cement, concrete, marble, sandstone,
and moss over concrete and marble. 51/68, 69, 78, 79.
This nitrophilous lichen is particularly common on the hypertrophicated
tops of limestone headstones in churchyards, concrete roofing tiles and
asbestos-cement roofs, either by farms or under partial tree shade (where
it benefits from bird lime-droppings). It is sparingly fertile. This species is
frequently the dominant member of the Physcietum caesiae union, although
this dominance may be shared with Physcia adscendens, P. orbicularis and
Physconia grisea.
P. nigricans (Florke) Stiz.
Scarce on asbestos-cement. 51/69.
Asbestos-cement roof, Havering's Grove, Hutton (1972, SJH); corru-
gated asbestos-cement roofs, disused barracks, Langdon Hills (1974,
PME-B).
P. orbicularis (Neck.) Poetsch
Very common on asbestos-cement, concrete, mortar, limestone, marble,
sandstone, brick and moss over concrete and limestone; scarce on de-
corticate parts of Salix and Ulmus; also recorded on roofing-felt. 51/68,
69, 78, 79.
The commonest species of Physcia in the area.
This species is frequently associated with Physcia caesia in the Phy-
scietum caesiae, although it does show an affinity for damper situations
such as damp vertical surfaces and the channels of corrugated asbestos-
cement roofs. A good example of the Physcietum caesiae is present on the
asbestos-cement roofs of an old, disused army barracks at Langdon Hills.
Here, the Physcietum caesiae consists of Caloplaca citrina, C. decipiens,
C. holocarpa, Candelariella aurella, Catillaria chalybeia, Lecania erysibe,
Lecanora dispersa, L. muralis, Lecidella stigmatea, Physcia caseia, P.
nigricans, P. orbicularis (dominant), P. tenella, Rinodina subexigua,
Verrucaria muralis, Xanthoria aureola and X. parietina.