| Site of Special Scientific Interest | |
 | |
  Location within Somerset | |
| Location | Somerset |
|---|---|
| Grid reference | ST619454 |
| Coordinates | 51°12′24″N 2°32′48″W / 51.20653°N 2.54676°W / 51.20653; -2.54676 |
| Interest | Biological |
| Area | 0.84 hectares (0.0084 km2; 0.0032 sq mi) |
| Notification | 1972 (1972) |
| Natural England website | |
Windsor Hill Marsh (grid reference ST619454) is a 0.84 hectare biological Site of Special Scientific Interest, north of the town of Shepton MalletinSomerset, and adjacent to the Windsor Hill Quarry geological Site of Special Scientific Interest. It was notified in January 1972.
Windsor Hill Marsh is a marshy silted pond, with adjacent damp, slightly acidic grassland. Adjoining the marsh are a limestone bank, and a short stream which flows into a swallet.
The site is of interest for its diverse flora, in large part down to the varied habitats present within the small area. English Nature's SSSI citation sheet states that 114 species have been found at the site. Two species are present which are rare in Somerset: flatsedge (Blysmus compressus) and slender spike-rush (Eleocharis uniglumis). Flatsedge was discovered here in 1946 by Humphry Bowen. This species occurs at no other site in Somerset. Slender spike-rush was discovered in 1972 by Florence Gravestock, and is only found at one other site in Somerset, West Sedgemoor. Both species were still present in 2004. Other marshland plants found here include purple loosestrife, yellow flag (Iris pseudacorus), hard rush (Juncus inflexus), soft rush (Juncus effusus), flowering rush (Butomus umbellatus), devil's-bit scabious (Succisa pratensis), three species of horsetail Equisetum spp. and seven sedges Carex spp.
