*1: Mousehole Cave, 1859, WC
(PNZ) (Paton 1969a:
752).
*2: Probus, 1861, ES
(TRU) (Paton 1969a:
752).
An aquatic or semi-aquatic moss that can vary
widely in appearance even when only submerged forms are
studied (Wehr & Whitton 1986). Some fertile plants with
small leaves from sites high in the flood-zone are much
smaller and softer than the usual aquatic forms and might be
mistaken for Rhynchostegium
confertum, but their leaves are more rounded and the
spores are larger.
Forms patches (smooth mats) or occasionally extends
as pendant wefts on vertical surfaces where water trickles or
spray lands. Habitat notes from C&S are as follows. Grows
mostly on rock and boulders (gabbro, granitic, serpentinite,
slate), masonry, concrete, tree roots or hard soil in and
beside water, sometimes also established on firm mud. Mainly
found from ca 10 cm
below normal summer water-levels to 50 cm or more above them,
but usually within the flood-zone (except occasionally in the
most humid and shaded places); also on rocks receiving spray
from waterfalls. Sometimes found in the open, commonly partly
to moderately shaded, occasionally in rather heavy
shade.
Habitat types occupied are mainly along streams and
rivers (both hard- and soft-water, oligotrophic and
eutrophic), sometimes mere trickles or in spray from
waterfalls, or flushed rocks in quarries or on sea-cliffs
(down to near HWST level). It apparently prefers sites with
fast-flowing water, such as at weirs and other obstructions,
but was also recorded occasionally from ditches, along the
Bude Canal and the inundation zones at edges of two
reservoirs. Once seen well established on concrete around a
leak in a water trough in pasture.
Evidently tolerant of hypertrophic conditions in
streams since it was found in pure stands on vertical concrete
of the outlet channel at one sewage works and not far below
the outlet from another. It is often the only bryophyte in
eutrophicated streams below sewage outlets, typically
occurring just above normal water-level in these situations
rather than submerged (presumably because it can grow only
where high concentrations of pollutants are diluted during
high-stage river discharges).
Often occurs as pure patches, but its closer
associates frequently include Chiloscyphus
polyanthos, Fontinalis
antipyretica var. antipyretica, Fontinalis squamosa,
Hygrohypnum
ochraceum, Scapania
undulata, less commonly Cratoneuron filicinum,
Fissidens
crassipes, Fissidens pusillus, Leptodictyum riparium,
Platyhypnidium
lusitanicum.
Commonly c.fr.: capsules immature 1, 7-12;
dehiscing 1-3, 9-12; dehisced 1-5, 11. Some large populations
of robust plants on rock in streams apparently do not bear
capsules, especially where they grow permanently submerged,
while small slender plants in rather dry sites may fruit
freely.