Purn Hill is a 6.1 hectare

Hectare

The hectare is a metric unit of area defined as 10,000 square metres , and primarily used in the measurement of land. In 1795, when the metric system was introduced, the are was defined as being 100 square metres and the hectare was thus 100 ares or 1/100 km2...

 biological Site of Special Scientific Interest near the village of Bleadon

Bleadon

Bleadon is a village and civil parish in the historic countyof Somerset, England. It is about south of Weston-super-Mare and, according to the 2001 census, has a population of 1,068.-History:...

, Somerset

Somerset

The ceremonial and non-metropolitan county of Somerset in South West England borders Bristol and Gloucestershire to the north, Wiltshire to the east, Dorset to the south-east, and Devon to the south-west. It is partly bounded to the north and west by the Bristol Channel and the estuary of the...

, notified in 1990. The site is a small promontory

Promontory

Promontory may refer to:*Promontory, a prominent mass of land which overlooks lower lying land or a body of water*Promontory, Utah, the location where the United States first Transcontinental Railroad was completed...

 of Carboniferous Limestone

Carboniferous limestone

Carboniferous Limestone is a term used to describe a variety of different types of limestone occurring widely across Great Britain and Ireland which were deposited during the Dinantian epoch of the Carboniferous period. They were formed between 363 and 325 million years ago...

 projecting southward from the main Mendip

Mendip Hills

The Mendip Hills is a range of limestone hills to the south of Bristol and Bath in Somerset, England. Running east to west between Weston-super-Mare and Frome, the hills overlook the Somerset Levels to the south and the Avon Valley to the north...

 ridge.

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

Salad Burnet

Sanguisorba minor is a plant in the family Rosaceae that is native to western, central and southern Europe; northwest Africa and southwest Western Asia; and which has naturalized in most of North America...

 (Sanguisorba minor), Dropwort

Dropwort

Dropwort , also known as Fern-leaf Dropwort, is a perennial herb of the family Rosaceae closely related to Meadowsweet...

 (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

Dolostone

Dolostone or dolomite rock is a sedimentary carbonate rock that contains a high percentage of the mineral dolomite. In old U.S.G.S. publications it was referred to as magnesian limestone. Most dolostone formed as a magnesium replacement of limestone or lime mud prior to lithification. It is...

 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 (H. nummularium) to form the hybrid H. x sulphureum. 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 occurs here.

The Mendip Way

Mendip Way

The Mendip Way is an long-distance footpath across the Mendip Hills from Weston-super-Mare to Frome. It is divided into two sections.The West Mendip Way was opened in 1979 and starts at the Bristol Channel at Uphill Cliff. It climbs the Mendip escarpment affording views over the Somerset Levels....

crosses the site.

Source

• English Nature citation sheet for the site (accessed 17 July 2006)