The Essex Naturalist 131
MOSS & LIVERWORT FAMILIES OF SOUTH EAST ENGLAND. I
This series is intended to assist beginners with the recognition and identification of moss and liverwort species
belonging to families that are critical to identify. In addition to key identification features, the distribution,
abundance and ecological preferences, specifically related to their occurrence in the south east, are given for
each species.
I. PLAGIOTHECIACEAE
This is a family of mainly subtropical-tropical pleurocarpous mosses, with irregularly branched shoots, that are
characterized by leaves that are twisted above their helically arranged insertions so that they lie more or less
in one plain, giving the shoots a flattened (complanate) appearance, though scarcely so in Herzogiella. The
leaves on both the main stems and branches are identical, and those of most species have a characteristic short
double nerve. Vegetative propagation by bunches of green, spindle-shaped (fusiform) gemmae, produced in the
leaf axils, is common in many species, and some also produce fusiform gemmae from the leaf tips. In the south
east, they occur on humus rich soil, or on tree bases, in woodland and in hedgebanks. Characters useful for
identification are leaf shape, cell dimensions in mid-leaf, the degree of overlap of adjoining cells, presence or
absence of undulations of the leaf lamina, the shape and cell structure of any decurrent leaf bases or auricles,
the presence or absence of marginal denticulations near the leaf tips, the extent to which the capsule is straight
or curved, (and the angle at which the capsule is mounted on the seta), the colour of the plant en masse, and
the degree of shrinkage on drying.
N.B. Three non-plagiotheciacean genera found in the south east, Neckera, Homalia and Hookeria also have
complanate shoots with similar branch and stem leaves. Beginners are advised to learn these first before tackling
members of the Plagiotheciaceae.
[To identify a suspected member of the family, remove several leaves as completely as possible by gripping with
fine forceps and pulling downwards (away from the shoot tip), and mount in water under a coverglass on a
microscope slide. Measure the length and width of several cells mid-way from the base to apex, and mid-way
from margin to nerve. You will need a calibrated micrometer eyepiece scale to measure the cells. Then isolate
a still-attached leaf or two on a segment of stem, by pulling off any leaves that are overlapping them above and
below and obscuring their attachment to the stem. Mount the segment in water so that you can observe their
bases in situ under the microscope. If the margin of the leaf continues down the stem as a narrow extension,
more or less in line with the leaf, it is simply said to be decurrent. Where however the decurrent extension
widens out like an ear it is called an auricle. Of the taxa dealt with here, only members of the P. denticulatum
agg. have auricles. N.B. the fusiform gemmae (and twiglet propagules of J. elegans) detach readily and can be
lost when the plants are dried or immersed in water. They are therefore best observed in fresh material].
KEY TO GENERA OF THE PLAGIOTHECIACEAE FOUND IN SOUTH EAST ENGLAND
(N.B. this key is artificial and applies only to the species included here)
1 Lf bases decurrent................................. 4 (PLAGIOTHECIUM)
c. 100 species worldwide
Lf bases not decurrent............................ 2
2 Lf apex acute....................................... 13 (TAXIPHYLLUM)
c. 36 species worldwide
Lf apex filiform.................................... 3
3 Lf margin +. denticulate throughout;
twiglike deciduous shoots absent................ 11 (HERZOGIELLA)
c. 3 species worldwide
Lf margin, entire or denticulate only at apex;
twiglike deciduous shoots usually present..... 12 (ISOPTERYGIUM)
c. 270 species worldwide