Helosciadium repens, Creeping Marshwort
Creeping Marshwort, Helosciadium repens is a European Protected Species as well as being on Schedule 8 of the CROW Act and Section 41 of the NERC Act. It grows in the Canaries, northern Morocco and is rare in the Netherlands, Belgium, France, Spain, Slovenia, Germany, Switzerland, Austria and Turkey. It was once widespread in the UK, occurring in Scotland, Wales, Yorkshire and East Anglia, but always rare. Recently it has been confined to Port Meadow, Oxford (now an SAC) but recurred temporarily at Binsey Green and was introduced to North Hinksey. In 2002 it was found by Brian Wurzell in the Lee Valley SSSI in Essex, but after disappearing for several years, it has now reappeared following more intensive grazing and management. It has also appeared in Suffolk following clearance.
Note that this species used to be known as Apium repens but is now Helosciadium repens. Similarly Apium nodiflorum is now Helosciadium nodiflorum.
Following the Rio Convention in 1992 the Joint Nature Conservation Council commissioned the Plant Sciences Department of Oxford University to make a DNA study of the Oxford and continental material and it was confirmed that the Oxford plants were the real thing dispelling fear that only the hybrid with Helosciadium nodiflorum survived. It was then entered into English Nature’s Species Recovery Programme and conservation actions have been supported ever since by Natural England.
Annual monitoring of the main area was undertaken, showing a mobile population that was killed by summer flooding and very seldom flowered. The population returned by germination of seed from the soil seed bank until in 2009 prolonged flooding lasting over two summers killed this part of the population and all other plants due to “summer fouling” which is when levels of oxygen fall in the soil due to respiration, and then sulphates are reduced to the highly toxic sulphides. This area emerged as bare mud.
Recolonisation started with bistorts (Persicaria) and Speedwells (Veronica catenata and V. scutata).
Perennial vegetation did not return till until 2017. It had changed, though; Mudwort (Limosella aquatica) is now frequent, but Tubular Water-dropwort (Oenanthe fistulosa) has gone.
Holland and Belgium
A visit to Holland and Belgium in 1997 enabled us to meet people there who were also concerned about Creeping Marshwort. We saw the plant in a variety of conditions: a mown lawn in a rose garden; a water-logged bomb crater in the dunes where it had suffered frost damage; a river bank grazed by geese, and a recently unmanaged reedbed where it was very etiolated (tall, spindly and yellowish). Since then Anne Ronse in Begium has been making a detailed study of growth of Creeping Marshwort under experimental conditions.
As part of the Species Recovery Plan new populations were to be established in the wild. The only successful such introduction to date is that at North Hinksey, Oxford, where 20 plants were planted out in 1997; these plants have now spread to cover an area over 50 m long and have “jumped” to form new patches 10 m and 20 m distant.
An attempt was made to restore the population at Binsey by reintroducing intensive grazing. This was successful, but the sward has since become too dense and the plant has disappeared again. Restoration was also tried at Cogges, Witney by removing the sward, setting the topsoil on one side, excavating a scrape and replacing the topsoil, but the efforts were in vain.
An experimental study of submergence of Creeping Marshwort was carried out at the Oxford University Botanic Garden. This showed that when plants remained submerged during the summer they floated free of the soil.
Experiments were also carried out in people’s gardens to test whether the plants were self fertile; they were, slightly.
Historically, the hybrid with A. nodiflorum, A. x longipedunculatum (F. W. Schultz) Rothm., was suspected to be on Port Meadow. It has recently been found by Judy Webb and has been confirmed by DNA analysis. This hybrid is now being used to test potential introduction sites e.g. at Cutteslowe which in the floodplain of the Cherwell river, Oxford.
For more information about Creeping Marshwort see the report covering the work undertaken from 1995-2005. This report was written by Dr Alison McDonald and Dr Camilla Lambrick and is published on the Natural England website.
This work is funded by Natural England and is greatly assisted by the Oxford City Council, the Oxford Preservation Trust, the Oxford Botanic Garden, the University of Leicester, the Environment Agency, and many volunteers, most notably Alison McDonald, Camilla Lambrick and Judy Webb, the current Flora Guardian.