Thorney Island on the West Sussex coast is an area of low intensive farmland and salt marsh, surrounded by tidal mudflats and sandflats.

A large part of the Island is owned by the military but managed for its wildlife value by the Chichester Harbour Conservancy.

Thorney Island is well known as an internationally important bird area, but less known is the presence of a diminutive plant called Grass-poly Lythrum hyssopifolia. This small creeping plant with single pink flowers requires winter wet habitats which dry out in summer, and where there is heavy disturbance once a year to trigger germination. This can include pond habitats but may also include winter wet fields and both are found at Thorney.

Grass-poly has declined significantly across most of its historic range and is now classified as endangered. In 2017, over 500 plants were recorded from Thorney making it one of the largest and last remaining sites in the UK. We have been working at both local and national levels to standardise monitoring for Grass-poly and to raise the profile of this unique site.