*2: On rock shallowly
submerged on edge of river shaded by woodland, River Tamar
below Clitters Wood, SX47G, DTH 98-362 (BBSUK,
DTH) (Rothero 1999b:
41).
Known inCornwall
only by four recent records from rocks submerged in the River
Tamar. The species is likely to occur more widely along the
Tamar since three of the finds resulted from prolonged
searches for Pearl Mussels Margaritifera
margaritifera carried out by wading to search the river
bed in summer when water levels were low using 'glass-bottomed
buckets'.
Grows as more or less dense patches or more
extensive low (1-3 cm) lawns up to ca 30 cm in diameter.
Recorded only from the horizontal or sloping upper surfaces of
slaty rocks (bedrock, cobbles and boulders) permanently
submerged in water that is slow- to quick-flowing and 5-30 cm
deep at times of low summer water-levels. The largest
populations grew partly shaded by edges of deciduous woodland,
but others were in the open. It mainly grows in pure patches,
but sometimes mixed with sparse Fontinalis squamosa;
Fontinalis antipyretica
var.
antipyretica and lichens sometimes also occur close by.
The species is thought to tolerate water that is somewhat
polluted (C. D. Preston & A. J. E. Smith in Hill et al. 1992: 205) so
that it may have colonised the Tamar or at least increased
there as a result of eutrophication of the river resulting
from sewage inputs and agricultural
runoff.
Not seen c.fr. [capsules are unknown in British
Is.].
