Rare Plants Group Apium repens

Apium repens, Creeping Marshwort

What is it?

This insignificant little umbellifer is one of Oxfordshire's rarest plants. For a long time its only UK locality was on Port Meadow at Oxford and it is endangered in Europe. Attention was drawn to it after the Rio convention in 1992 and we have been monitoring its up and downs on this open access site ever since. Flooding is part of its natural cycle, but summer flooding can bring population crashes There has been successful introduction to one new site and it has returned following suitable management to another in Oxford and one in Essex. Its future depends on partnership, with Natural England, the Environment Agency and Oxford City Council playing leading roles.

Apium repens
Apium repens

Does it grow anywhere else?

Creeping marshwort is known in the Atlas Mountains of Morocco and in the Canaries. In Europe it is widely scattered but never common, being found in the Czech Republic, Italy, Spain, France, Belgium and Holland. It grows in a wide range habitats from mown graves in Austria, river-side gravel banks in Slovenia, under water in Italy, to slightly saline pasture and dune slacks in Holland. Creeping marshwort has always been rare in England and Scotland with sites in Essex, Norfolk, Yorkshire, Fife and Argyle. During the 1960s it was only known at three localities in Oxfordshire, but by the 1970s only one site in the whole country.

The Oxfordshire Sites

Witney

The West Oxfordshire site at Witney had been subjected to improved drainage and treated with herbicide, leaving a species-poor, grassy field. The Environment Agency dug a scrape designed to enable buried seed to germinate in damp conditions, but although a number of other interesting species appeared there is still no creeping marshwort.

Binsey

The common land at Binsey, just across the river Thames from Port Meadow, had been enclosed and rented out by the city. A brief time under the plough in the 1970s reduced the floral interest but following restoration and an extensive cattle grazing regime, a number of species have returned including creeping marshwort, bristle club-rush and tubular water-dropwort. The field is designated as a Site of Local Importance for Nature Conservation.

The Introduction Sites

As Apium repens is so rare, it has been considered important to introduce the plant to new locations. Plants were grown from collected seed and were bulked up in the University of Oxford Botanic Garden. Two places around Oxford were tried for the introductions. At New Marston SSSI a damp pony field looked suitable, but the plants soon disappeared, probably eaten by geese. At South Hinksey a pony paddock owned by the Oxford Preservation Trust has proved successful and the plants have spread and flowered well. During 2007 the plants were under water for most of August, but never-the-less dried out enough to flower in September.

Monitoring

Creeping marshwort is monitored annually by volunteers. On Port Meadow, two areas are marked by buried transponders (devices which respond to a radio signal from a retriever) and plants are counted or mapped. This has shown that they move about both by runners and by seedlings germinating from the seed bank in the soil. This is particularly important when mature plants are knocked back by summer flooding. Flooding affects plants most in summer when microbial activity means that oxygen levels in the soil can drop and a build up of ethanol and hydrogen sulphide can reach toxic levels.

Port Meadow
Monitoring on Port Meadow

Port Meadow is part of the Oxford Meadows Special Area of Conservation and the Environment Agency and Natural England have contracted studies by the Open University of the water level regime and likely impacts.

Future Action

A steering group meets as required to discuss water level management on Port Meadow. The interests of commoners cattle and horses, as well as public access and migrating birds have to be considered.

Floods
Floods on Port Meadow: looking approximately north east from the raised area at the south end of the meadow. The south population area is in the foreground with the civil war defences showing up as strips of grass at right angles, and the north population area is in the distance.

Further introduction sites in Oxfordshire and in Essex are being sought.

2009 Update

After the dramatic floods of late July 2007 water continued to lie on the lowest parts of Port Meadow through till autumn 2008. This had already stimulated us to discuss the impact on creeping marshwort in December 2007, and after the water remained high throughout the spring of 2008 the City Council called another meeting with Natural England and the Environment Agency to discuss drainage of water from Port Meadow.

Ditch
An old silted-up ditch which carries water westwards off the main creeping marshwort area into the river (in background) at the southern end of Port Meadow.

We heard that the persistent water was perhaps not mainly the result of trapped rainwater but of water coming up through the gravel, possibly from channels further north. As result the high water might be difficult to remove just by surface drainage. Summer of 2008 brought more water which slowly retreated in August exposing mud on which the vegetation has died.

Dead Vegetation
Port Meadow looking north west on 1st September 2008, the main area for creeping marshwort now a sheet of mud with duckweed and water-mint at the edge.

Some creeping marshwort plants were found around the edge of its former areas, and a few were flowering quite high up against the track along the east side of the meadow. Further north by the entrance to Burgess Field more plants were found, but all were etiolated from sitting in water, and none were flowering. One consolation as we retreated in a rainstorm was refinding the rare slender spike-rush (Eleocharis uniglumis), truly finding a needle in a haystack. A week later autumn rain arrived and the Apium repens areas were under water again.

Thames
Concern for plants on Port Meadow or just doubt about the weather, a volunteer looking over the River Thames from Binsey as the river burst its banks again, re-submerging the main area for creeping marshwort which is straight across the picture towards Oxford.

The introduction site at North Hinksey is slightly higher and the raised water levels have been beneficial. Creeping marshwort was introduced to an area a few metres across and has now spread to cover an area some 50 x 15 m along a shallow depression.

Hinksey
A volunteer talks to one of the ponies at North Hinksey which have been maintaining the short sward which has proved favourable for the creeping marshwort introduced here on Oxford Preservation Trust land in 1996. The introduction area is in the foreground.

We were delighted to witness two plants actually doing long distance vegetative spread at this site. A floating plant had become detached from the soil. and previous experimental work has indicated that this happens probably because the roots are weakened by the anoxic conditions when water-logged. Floating on the flood-water such plants can be distributed to new areas, perhaps a nice mud bank somewhere downstream.

Floater
Creeping marshwort in the flood water at North Hinksey. It has been floating for some time, as can be seen by the coiling roots and rotten runner. We hope that renewed flooding carried it to pastures new.

However the wet conditions also made grazing difficult and at Binsey Green (the only other Oxfordshire site for creeping marshwort) a dense growth of grass has made the sward very thick. Sadly creeping marshwort was not seen this year, though it will probably come back as it did before. However we were pleased to find other rare plants flourishing, especially the tiny bristle club-rush (Isolepis setacea).

More information

For full details see the Ten Year Report on the Species Recovery Programme in English Nature Research Report no. 706, 2006 A W McDonald and C R Lambrick, Natural England report number ENRR706.