Area: 5.21 hectares.

Description and Reasons for Notification:

Tregonning Hill is located approximately 6 km west of Helston. The site is underlain by the Tregonning Granite, a detached outcrop of the Cornubian batholith. Zones within the granite were altered by kaolinization and have since been worked for china clay. Evidence of this previous mining activity is shown by the profusion of disused pits, gullies, spoil tips and granite debris that now litter the hillside. 

Much of the site supports western lowland heath dominated by heather Calluna vulgaris, bell heather Erica cinerea and western gorse Ulex gallii, with bilberry Vaccinium myrtillus and tormentil Potentilla erecta. The occurrence of cross-leaved heath Erica tetralix indicates wetter conditions. Scrub vegetation, dominated by european gorse Ulex europaeus, bracken Pteridium aquilinum and bramble Rubus fruticosus agg. has developed on the deeper soils of the hill slopes.

The major importance of the site is the occurrence of an extremely rare liverwort, western rustwort Marsupella profunda.* This species is found growing on bare outcrops of weathered granite within and around the old china clay workings. This vulnerable and rare species requires the retention of bare stones and rocky outcrops for its continued survival. 

Tregonning Hill is the only known British location for western rustwort and internationally it is restricted to this site in Cornwall and a few locations in Portugal and Madeira. 

In addition, a nationally scarce moss, bristle leaf Brachydontium trichodes, which is restricted in Cornwall to two sites, is present at Tregonning Hill. 

* Western Rustwort, Marsupella profunda is listed on:
Schedule 8 of the Wildlife and Countryside Act, 1981:
Appendix 1 of the Bern Convention:
Annex II of the EC Habitats and Species Directive (Council Directive 92/43/EEC)