*1: Trevaylor,
Penzance, 1863, WC (PNZ) (Paton 1969a:
713).
*2: Trehane near
Probus, 1861, ES (TRU) (Paton 1969a:
713).
A few gatherings appear absolutely intermediate
between F. dubius and F. adianthoides, e.g.
from fixed sand-dunes at Gwithian Towans, but most F. dubius are readily
separable on smaller leaf-cell size and presence of bistratose
areas in upper part of leaf.
Forms patches or lawns. Although not especially
common over much of Cornwall,
this species occurs in a curiously varied range of
habitats:
(1) Frequent on calcareous sand or sandy soil in
short turf of dune grassland on fixed dunes, extending onto
similar blown-sand areas on hillslopes (e.g. above dunes) and
light sandy soils blown onto cliffs. Associates include Barbula and Didymodon spp., Homalothecium
lutescens.
(2) On soil or thin soil over rocks, e.g. on partly
shaded or shaded banks and among rocks near streams and rivers
and in quarries (in open or in woodland), amongst unshaded
short turf on slope in old serpentinite quarry above
sea-cliffs, on heathy areas above serpentinite cliffs and
quarried slate/shale cliffs, tops of 'hedges' inland and near
cliff tops and on thin soil over old
concrete.
(3) Directly on rock (serpentinite, slaty, less
often granitic), old concrete or mortar of mortared walls
(e.g. of viaducts, bridges and wall of mill-leat), on
horizontal to vertical surfaces, where at least some base is
probably present. Occurs on both wet (flushed) and rather dry
rocks and concrete, in open and unshaded to rather heavily
shaded and sheltered places. The records include boulders near
outcrops, rocks on and above sea-cliffs, a disused railway
cutting, quarries and a stony path.
(4) Five records of patches on tree bark: in some
quantity 1-2 m above ground on old oak in deciduous woodland
(W. of Lerryn); single patch low on large oak tree near stream
in edge of deciduous woodland (near Callestick); low on old
Ash trees, once part-shaded in woodland near stream, once near
coast; patch on silted bark of tree low in flood-zone beside
R. Tamar.
Infrequent (11) records c.fr. (but at least 3 of
them with capsules abundant): capsules immature 1, 2, 11, 12;
dehiscing 1, 2, 3*; dehisced 1, 3, 5, 6, 9 [* = plants
apparently intermediate with 30.17].
