Water-primrose – an unwelcome arrival

    All photos © Bert Reid 2011

A large patch of a creeping, yellow flowered plant with long trailing non-flowering stems reaching into the water was found on the marginal mud of a pond near Bishampton. The structure of the flower showed it to be in the Willowherb family and the genus keyed out to Ludwigia (Hampshire-purslanes). The only plant with obvious yellow flowers and alternate leaves mentioned in the most recent British flora is Ludwigia grandiflora, the Water-primrose.  This is recorded as an established aquarists’ throwout in ponds in Surrey and S. Hants. 
Water-primrose is included as a red alert species on DEFRA’s Non-Native Species Secretariat where they ask for all sighting in the UK to be reported. It has become a serious pest in parts of Europe, especially France, where it has spread rapidly, choking waterways, increasing flood risk and crowding out native species. The Environment Agency is attempting to eradicate the plant in all known sites. This sighting has been reported and is the first in Worcestershire and about the 18th in the UK since the first record in 1999.
Questions concern the exact identity of the plant.  It appears that France has more than one species, and the botany section of the Smithsonia Institute website has a section on Ludwigia with about 90 taxa fully described.  The three species noted in Europe are all in this section, but seem to mainly differ from each other in chromosome numbers.  Not for certain field identification!
 So our only Worcestershire record for this attractive and interesting water plant may be eradicated without even being definitively identified!

Click here for the full text of Bert's report.