132 The Essex Naturalist
KEY TO SPECIES Leaves decurrent:
Lvs greyish-green, transversely wrinkled, 2-5mm long;
Mid-lf cells only 8-9um wide, plants large, robust, with long straggly
markedly flattened shoots. Very local in S.E. England and very rarely in fruit,
sloping banks under trees in sheltered sites with moderate shade, occasionally
growing over Sphagnum. Calcifuge............. Plagiothecium undulatum
Lvs yellowish-green to dark green, not or only slightly
undulate (see P. ruthei), rarely exceeding 3.2mm long............... 5
Most mid-lf cells less than 10um wide.................................... 6
Most mid-lf cells more than 10um wide.................................. 8
Lvs symmetrical, tapering to a long acuminate apex;
Margin entire or faintly denticulate near apex, long decurrent in single
row of elongated cells, somewhat shrunken when dry, cells in mid-lf
6-8um x 80-150um, fusiform gemmae often present in If axils and on lf tips.
Shoots slender and semi-erect. Glossy, yellowish green, on decaying logs,
fern shuttlecocks, tussock sedge stools, tree bases - usually in wet but
sometimes in quite dry situations. Rarely found in fruit and very local in
the S.E............................................ Plagiothecium latebricola
Most lvs asymmetric with one side +. straight, or with one side flat and the
other broadly folded across;
Margin entire or faintly denticulate near apex, scarcely altered when dry,
long decurrent in 1-4 rows of narrow rectangular cells. Cells in mid-leaf
linear vermicular, 6-10um x 85-145um.................................... 7
Lf apices characteristically curved downwards when moist, not undulate,
leaves 1.0-2.6mm long, decurrent bases to (D3-4 cells wide:
Fusiform axillary gemmae occasional. Young capsules dark preen, inclined
and curved, sporophytes common in S.E. England. Glossy, pale green, often
very pale in exposed situations. Tree stumps, logs, leaf litter (including
conifer needles) and humus rich soil. Widely distributed on neutral to
strongly acid soils............................. Plagiothecium curvifolium
Lf apices not curved downwards when moist, sometimes undulate when
dry, l-2mm long, decurrent bases to 1-2(3) cells wide:
Fusiform gemmae usually present in lf axils and on leaf tips. Young capsule
pale green, slightly inclined to erect ±_ straight. Plants yellowish-green,
smaller than P. curvifolium, in very glossy smooth tufts, shoots short and
fragile. Rare and sporadic in the south east, on tree bases and stumps in
woodland, on neutral to mildly acid soils.. Plagiothecium laetum
Lvs mostly asymmetric, cells of decurrent bases rounded to rounded
rectangular and forming distinct auricles............................... 9
Lvs mostly symmetrical, cells of decurrent bases rectangular,
Scale bar = 1mm (leaf outlines) not rounded, and not forming distinct auricles......................... 10