5
eastings first then northings, or in at the door before going up the stairs.
Hydrocotyle ranunculoides
Can you please let me have any new records for this aquatic alien which is spreading like wild
fire, before trying to pull it all out of any pond or stream you find it in! Its very easy to mistake
for well-grown H. vulgaris. Two diagnostic characters will clinch it. The leaves of H. vulgaris
are peltate, that is, circular with a centrally inserted petiole or leaf stalk. In H. ranunculoides
the lamina appears to be peltate but there is a slit on one side that reaches the centre. It may
however be obscured by the overlap of the two edges. The petioles are fat and spongy (c.5mm
diameter), and glabrous, whereas those of H. vulgaris are somewhat wiry and spindly
(c.l-2mm diameter) and usually thinly clothed with a few fine spreading hairs.
Lemna minuta (=minuscula)
This tiny alien Duckweed is now widespread in Essex and almost certainly occurs in every
10km square. But beware tiny forms of L. minor during the winter months.
GRASS GRIPES
'AGROPYRON'
Hopefully this genus will one day be reinstated! Meanwhile we have to put up with Elytrigia
repens (= Agropyron repens) and Elymus caninus (Agropyron caninum). Please be careful in
recording caninus/um. It is a relatively uncommon, distinctly droopy plant of woodland
margins, and grows in tufts without rhizonies. On the other hand the awned form of the
rhizomatous repens is common in all sorts of habitats, including woodland.
AGROSTIS
This is probably the most difficult genus of British grasses to identify, and to quote Tom Cope
at Kew, who is producing a new book on British Grasses, there is no getting away from having
to dissect the one-flowered spikelets (by removing the two enclosing glumes) to see if the
palea is vestigial or well developed, and to see whether the awn on the lemma, if present, is
inserted near the base, on the back or on the tip. Identification is also frustrated by the need
to have the flowers at anthesis to see the palea, and in post-anthesis to see the position of the
closed panicle! As a double check, the small (vestigial) palea character is correlated with a
long pointed ligule, whereas a well developed palea correlates with a short truncate ligule.
Another character that gives difficulty is the position of the spikelets in the panicle. If these
are largely confined to the outer branches the panicle appears to be a hollow cone, whereas
if the spikelets occur on the lower branches the density of the panicle appeals to be even
throughout. This is very obvious in pressed material. The presence or absence of an awn is not
a good character, as for example, A. stolonifera often has an awn, whereas some forms of A.
castellana sometimes do and sometimes don't. Of more importance is the position of the
insertion of the awn. So while you are dissecting your spikelet with a fine pair of forceps or
a mounted needle under a lens or microscope to look for the palea, make a note of whether
any lemma awn present arises from the base, back or tip of the lemma.
Essex Field Club Newsletter No. 19. November 1996