Rockrose - hoary or otherwise

Yesterday I visited Prestatyn Hillside SSSI with the CCW Conservation Officer for the site, to undertake some monitoring/ mapping of Helianthemum oelandicum, hoary rockrose. We were hoping that despite the lateness of the season we would be able to tell this species apart from the closely related Helianthemum nummularium, common rockrose. In fact once we got our eyes in it wasn't too difficult, with a significant difference in the size of leaves and prostrate-ness of the plant, the presence of stipules on H. nummumlarium but not on H. oelandicum, and the more dense hairiness of H. oelandicum. The small, low clumps of H. oelandicum were fairly easily picked out even when surrounded by large areas of H. nummularium. 

H. nummularium is common in calcareous habitats, while H. oelandicum is scarce in Britain and is restricted mainly to coastal areas, with North Wales being one of its hotspots. On Prestatyn Hillside it seems to favour areas around limestone outcrops, where the soil is thinner and presumably competition is less intense. H. nummularium is found throughout the site including in moderately coarse grassland where it is able to hold its own.

Helianthemum oelandicum, hoary rockrose

Helianthemum nummularium, common rockrose

 We were able to identify three areas with H. oelandicum, and another, steeper outcrop which we were unable to visit may well provide habitat for a fourth area.

The greatest threat to this site (which is designated for an assemblage of rare or scarce plant species) may be from invasive scrub, including several Cotoneaster species. As it is very steep and not fenced grazing presents multiple challenges and is unlikely to be a practical option, so the continuing scrub clearance which is being carried out by hand is probably the only option. Some areas of good habitat, however, would be lost if this scrub clearance (which appears to have been successful in recent years) was not continued.

Cotoneaster spp. together with native scrub spreading over the hillside