Hybridisation of a wild flower in north London

Overview of Silene records for greater London from 2000 to 2010.
Overview of Silene records for greater London from 2000 to 2010.

During summer 2010, Open University student, Michael Hartup, supported by GiGL species data, investigated hybridisation between white campion Silene latifolia and red campion Silene dioica in north London.

GiGL provided Michael with campion species records for the previous ten years so that he could identify a site with a suitably large population of this wild flower to investigate.

By reviewing the species data, Barn Hill in north London was chosen as a study site because of a high density of red campion records. A second study site, 8 Km east of Barn Hill at Hampstead Heath, was also selected.

The habitat and underlying soils at the two sites were different. Barn Hill, within Frient Country Park, is an area of traditionally managed hay meadow (semi-improved grassland and species rich grassland) with some deciduous woodland, the campions here grow by the meadow path, screened by shrubs and low trees at the woodland edge.

Hampstead Heath is mainly acid grassland and ancient woodland and the campion population is set in a shaded woodland clearing. Michael was interested to find out if the genetics of the two populations was different due to their differing isolation and habitats.

A sample of individual plants at each site was chosen to record characteristics that vary between red and white campion. Characteristics recorded included leaf and calyx size and shape, petal colour, seed colour and texture and if a night-time scent is produced.

Scoring of these variable characteristics produced a character profile for each site, from which the levels of hybridisation within each population can be inferred.

Results indicated that, although there are currently no white campions at either the site, the red campion population at Barn Hill includes a notable level of hybridisation with the white species. The level of hybridisation at Hampstead Heath however was significantly different, plants were much more strongly ‘red campion’ in their characteristics.

The reasons for these differences will require further investigation, but it is likely that the population at Hampstead is ecologically isolated from hybridisation and possible that the habitat there favours the characteristics of red campion, making hybrids with white campion less likely to flourish.

Silene records provided by GiGL, Greenspace Information for Greater London. Maps created with Open Source map data from the Ordnance Survey, using Quantum GIS. Soil data obtained with permission from the Greater London Authority.