Grass-poly Lythrum hyssopifolium

Best Time to See

A low-growing plant, with a branched stem that sometimes creeps along the ground.

In the early summer single pink flowers bloom where the leaves meet the stem.

Best time to see

Flowers from June to July.


Grass-poly has very specialised ecological requirements: it is a species of disturbed ground which is flooded or wet in the winter but which dries out in the spring, so can be found in the hollows and ruts of arable land and also damp pastures disturbed in winter by waterfowl. It requires water retentive soil.


It was once scattered throughout southern England, particularly around London, Cambridgeshire and Oxfordshire but it has now declined dramatically to a handful of sites.


It is classified as ‘Endangered’ and is therefore considered to be facing a very high risk of extinction in the wild. It is protected under Schedule 8 of the Wildlife and Countryside Act 1981. This makes it an offence to intentionally pick, uproot or destroy any plants. The species is also listed as a priority species under the UK Biodiversity Action Plan.

Key threats

Field drainage has limited the amount of wet arable habitat available so its need for very wet ground in winter is now rarely available. The introduction of broad-spectrum herbicides has also been a direct cause of decline.