Purn Hill (grid reference ST332573) is a 6.1 hectare biological Site of Special Scientific Interest near the village of Bleadon, Somerset, notified in 1990. The site is a small promontory of Carboniferous Limestone projecting southward from the main Mendip ridge.

Purn Hill

Site of Special Scientific Interest
Location within Somerset
Location	Avon
Grid reference	ST332573
Coordinates	51°18′40″N 2°57′32″W / 51.311°N 2.959°W / 51.311; -2.959
Interest	Biological
Area	6.1 hectares (0.061 km2; 0.024 sq mi)
Notification	1990 (1990)
Natural England website

The SSSI citation sheet describes the site as having an "exceptionally diverse unimproved calcareous grassland flora". The richest grassland communities are situated on the thin and stony soils of the steeper west-facing flanks of the hill. Over 200 species occur in the sward, including Salad Burnet (Sanguisorba minor), Dropwort (Filipendula vulgaris), Fairy Flax (Linum catharticum), Kidney Vetch (Anthyllis vulneraria) and Dwarf Thistle (Cirsium acaule). The rare plants are mainly associated with the small exposures of dolomitic limestone in the southern part of the site. Purn Hill is one of only five British sites for the nationally rare coastal limestone umbellifer species Honewort (Trinia glauca). White Rock-rose (Helianthemum apenninum) is found at the site and hybridises with Common Rock-rose (Helianthemum nummularium) to form the hybrid H. x sulphureum.^[1] Forty species of grass occur at the site, including Somerset Hair-grass (Koeleria vallesiana) which in Britain is confined to the western Mendips. Musk Stork's-bill (Erodium moschatum) occurs here.^[2]

The Mendip Way crosses the site.