The lichen vegetation of ferry-five acid watercourses in England is de
scribed and related to ecological variables. The zonation scheme adopt
ed for chalk and limestone streams that involves four overlapping band
s of lichen vegetation related to length of submergence is also approp
riate for this habitat. The flora involves around 90 species, a number
of which are rarely recorded specialists. Evidence is presented that
substratum chemistry is a more powerful ecological factor than water c
hemistry. An attempt has been made to relate the lichen flora to homog
eneous stream segments from the headwaters down to the alluvial lowlan
ds. An investigation into the effects of water quality showed that bot
h suspended solids (silting) and eutrophication are highly deleterious
to the lichen flora; the submerged and fluvial mesic zones are the fi
rst to be affected. The zonation across streams in England is compared
with those reported from Germany and found to be closely similar. (C)
1997 The British Lichen Society.