Corky-fruited Water-dropwort: a new record for this very scarce London species in Bexley

On 23rd July 2014 a number of plants of Corky-fruited Water-dropwort (Oenanthe pimpinelloides), a member of the carrot family, and a species of conservation concern for Greater London due to its rarity in the capital, were found in an uncultivated field by Bexley Natural Environment Forum Vice-chair Chris Rose, on a tour of privately-owned land in the Coldblow area of the Borough, not far from the Kent border.

The plants stood out as not being Wild Carrot, but since he had only seen the species once before, many years ago in Bristol, and was not carrying any field guides, some sample material was collected. This has just belatedly been identified. In particular, the corky swellings at the base of the seed capsules can be seen on the densely-packed dried flower head, and the spiky erect styles are also prominent.

Corky-fruited Water-dropwort from Coldblow in the Borough of Bexley. An important new record of a species that is very scarce in London. Lower stem leaf to the left, seed head centre, and upper stem leaf on the right. (Photo: Chris Rose)

Very few previous records from within London, or around its border, were known at the time of Rodney Burton’s ‘Flora of the London area’ (1983), but a few more locations have been added since then, notably on a Council housing estate in Southwark, in which Borough the species is the subject of a biodiversity action plan. It is known to have spread into parks, commons and a golf course from a site in Bromley probably, thinks Rodney, through mowing contractors inadvertently distributing seed. Otherwise the species is not noted for its dispersal ability, so the Coldblow population may be an old one.

A Google Earth photograph purporting to be from January 1940 (though obviously not taken in winter) shows the field to be down to what is probably an arable crop, possibly a cereal, and with what appears to be an orchard on the south side. In a 1960 image the orchard seems to have gone, and the whole patch shows closely-spaced rows of a dark-leaved crop which might be small fruit bushes, or very large potato plants. By the time of the next aerial view in 1990, the area now inhabited by the CFWD is grass. It should be noted that the common name of the species is misleading, and it is in fact a native perennial of hay meadows and pastures, particularly horse-grazed pastures. It is usually found growing on acidic soils and will tolerate both damp and dry conditions. It does, however, have close relatives that do habitually grow in damp ground, in marshes or in water.

GiGL’s latest dataset shows records made by Margot Godfrey in 2000 and Jon Riley in 2002 from Woodland’s Farm, but on the assumption that the grid references given are deadly accurate, and using the ‘Wheresthepath’ online mapping site, both were from a field adjacent to the Greenwich/Bexley boundary, but on the Greenwich side of it. So this new record may be a first for the Borough of Bexley unless there were or are any plants in the adjoining field on the Bexley side of the border at the farm, which is marked by a hedge. It is possible that only a sample grid reference was given for the population as a whole, which just happened to be one lying within Greenwich. Inquiries are being made on this point.

The occurrence of the plant in Greenwich, in close proximity to Bexley, came to particular prominence during 2012 when concerns were raised in the media about the proposal to site a Rapier Missile Battery near the cafe in Oxleas Woods. This was in order to protect the Olympic Park from airborne terrorist attack, and the CFWD was cited as an important part of the local wildlife which could be damaged as a result. We also know that CFWD was still present on Woodlands Farm in 2010 in a spot further into Greenwich, thanks to a record submitted to GiGL by the farm’s Trust.

According to the Botanical Society of the British Isles News, January 2009, No. 110, in an article by Tony and Val Marshall, CFWD in Britain and Ireland  occurs almost entirely in southern England and the extreme south-west and south-east of Ireland. It is said to be quite frequent in south Hampshire, IoW, Dorset, east Somerset, east Devon and the Severn Valley into Gloucestershire. There are a few sites in Sussex, Kent, Surrey and South London. There are also a few isolated records further north in England.