9
BOTANICAL MEETING, RIVER STORT: 18th July 1993
Six members gathered at Twyford Lock. Rain was forecast for the day but in the event it
remained dry until the end of the meeting. In the morning we walked the one kilometre to
the Thorley Flood Pound. This is an area which is flooded at times of heavy rainfall. It
proved to be an area rich in rare and local marsh plants which are decreasing rapidly in
Essex due to loss of habitat. The margins of the river had many of the more common
water-side plants such as Purple Loosestrife Lythrum salicaria, Hemp Agrimony
Eupatorium cannabinum and Indian Balsam Impatiens glandulifera.
The flood pound has a large population of Common Valerian Valeriana officinalis in full
flower. Southern Marsh Orchid Dactylorhiza praetermissa was abundant but had almost
finished flowering. There were also a few plants of Early Marsh Orchid D. incarnata.
Other local plants present in quantity were Fen Bedstraw Galium uliginosum, Lesser
Water Parsnip Berula erecta, Marsh Ragwort Senecio aquaticus, Brown Sedge Carex
disticha and Blunt flowered Rush Juncus subnodulosus. The latter could be compared
with the much commoner Sharp flowered Rush J. acutiflorus. Around a shallow pond
Bristle Club-Rush Isolepis setacea was abundant whilst in the pond large fruiting
colonies of the Stonewort Chara vulgaris var.vulgaris occurred.
An area which is occasionally grazed revealed an interesting occurrence. Both Water-
Plantain Alisma plantago-aquatica and Narrow leaved Water-Plantain A. lanceolatum
were growing together in quantity. Although I have read of a difference in flowering time
during the day I have never seen the two species intermixed before to confirm it. The
time was 1pm and the flowers of A. lanceolatum were fully open whereas those of A.
plantago-aquatica were fully closed and would open later in the day. There was no sign
of any hybrids which have occasionally been reported when the two species grow
together. Some of the A. lanceolatum plants were as large as A. plantago-aquatica and
had leaves approaching the latters in width and this character had to be used with caution
when separating them.
After lunch we walked in the opposite direction along the Stort to Rushy Mead N. R.
There were a few large clumps of Greater Tussock Sedge Carex paniculata in a pond.
Both Common Hemp-Nettle Galeopsis tetrahit and Bifid Hemp-Nettle G. bifida grow in
the reserve and the subtle differences in corolla shape could be observed.
In the river a small colony of Sweet Flag Acorus calamus was pointed out by Charles
Watson showing the characteristic transverse wrinkling of the leaves. Shining Pondweed
Potamogeton lucens also grew in the river.
Tim Pyner