41
some quantity along the edge of the causeway
that cuts off the large lagoon at the north-
west corner of Hanningfield Reservoir. In
October he checked on the plants again and
found the mericarps were mature enough to be
certain on dissection that the subspecies was
occidentalis, the only one found sop far in
Britain. Unfortunately the mericarps on the
Kelvedon Hatch' plants all dropped off before
they were mature enough to dissect out of their
covering envelope to check their morphology,
but the fact that they aborted so readily
suggests they are the same subspecies.
C. truncata has a southern distribution in
Britain enclosed by the 60° F July mean
isotherm, its main stronghold being in the east
midlands (Notts., Lincs. and Leics.), where it
has been recorded from some thirteen 10 km
squares. Apart from a stable pocket in
Somerset, however, the rest of its localities
(in Kent and Sussex) are sporadic and pre-
carious. I would think it more likely that
our Essex plants have been introduced from the
nearby continent by migrating water birds than
from elsewhere in the U.K. Having established
a foothold it will no doubt turn up elsewhere
in the county. Look out for a Callitriche
with small reddish-green leaves and lacking an
emergent rosette.
KEN ADAMS