THE LICHEN FLORA OF THE BASILDON AREA 143
the total number of species of lichen present in the area occur in the church-
yards and a considerable percentage of these only occur in any numbers
or in well developed communities in this microhabitat. 11 % are entirely
restricted to churchyards since they are unable to colonise other calcareous
substrates, and this figure is probably an underestimation as a number of
very old churchyards within the area have not yet been studied in detail
or at all. It is interesting to compare the figures given by Laundon (1967)
for the species which grow in churchyards and cemeteries in the London
area (a radius of 16 km from Charing Cross) with the Basildon area, since
they are almost identical, with 62% in the Basildon area and 61% in the
London area. The importance of the churchyard habitat has been em-
phasised in a booklet resulting from a commission by the Board of Social
Responsibility of the General Synod of the Church of England (Barker,
1972).
The importance of calcareous substrates to lichens is due to their ability to
buffer acidic phytotoxicants. Concrete walls, posts, mortar and asbestos-
cement (which also has the added advantage of having a good water
retention capacity) as well as limestones are important habitats as is shown
by the fact that 50% of the species recorded from this area were growing
solely on these substrates. This is significantly less than the percentage
quoted by Laundon (1967) for London (66%), although this is largely due
to the paucity of the corticolous and lignicolous species in the London
area, whereas these constitute 34% of the total number of species in the
Basildon area.
Lichen Flora
The following list is based solely on the species recorded during the
present survey. The 10 x 10 km squares of the national grid from which
taxa have been recorded is noted together with some ecological and
phytosociological details. Nomenclature mainly follows James (1965,
1966). Voucher specimens of critical species are now housed in the her-
barium, Bankfield Museum, Halifax (HFX).
IMH =I. M. Harding (Mrs)
PME-B =P. M. Earland-Bennett
SJH =S. J. Harding
Acarospora fuscata (Nyl.) Arnold
Scarce on sandstone. 51/69.
Sloping arches of railway bridge, Hutton (1971, PME-B); horizontal
surface of chest-tomb, All Staints' churchyard, Hutton (1974, PME-B).
A. smaragdula (Wahlenb. ex Ach.) Massal.
Rare on brick. 51/69.
A few specimens on bricks of old kale beds, Norsey Farm, Billericay
(1973, PME-B).
Bacidia sabuletorum (Schreb.) Lett.
Scarce on soil and moss over limestone. 51/69, 79.
Limestone chest-tombs in churchyards of the Congregational Church,