Grass-wrack pondweed (Potamogeton compressus)

GenusPotamogeton (1)
SizeStem height: 0.5 - 0.9 m (2)
Stem diameter: 3 - 6 mm (2)

Classified as Nationally Scarce in Great Britain (3).

This submerged aquatic plant has very flattened, branching stems that can reach up to 0.9 m in length (4). The leaves are long and slender; they usually have five main veins running along their length, and are translucent (2). The small flowers are produced sparingly (3) on spikes (5). The Latin name Potamogeton derives from the Greek for 'river neighbour' and indicates the aquatic habits of this genus of plants (5).

This nationally scarce species has suffered a prolonged decline in the UK (3). At present it occurs in scattered sites in central England, coastal areas of Norfolk, the Welsh borders and a single site in Scotland (6). It is widespread in temperate Eurasia (7).

Occurs in either still or gently flowing water and has been recorded in a variety of aquatic habitats including rivers, ox-bow lakes, canals, lakes in low-lying areas and ditches (3).

Most populations produce very few flowers and new plants are produced mainly from special modified branches called 'turions', which start to form in early June (3).

A number of threats to this species have been identified, including eutrophication (nutrient enrichment) of the water bodies it inhabits, recreational pressures such as boating and the resulting pollution and churning up of the sediment, as well as the neglect of canals and ditches (3).

Grass-wrack pondweed is a UK Biodiversity Action Plan priority species, and a Species Action Plan has been produced to guide its conservation. The action plan aims to maintain and enhance the current UK range of the species and encourage it to spread to new sites (3). In addition, a programme of research has been proposed to investigate the requirements of this plant and ways to conserve it (3).

Information authenticated by Richard Lansdown.

  1. National Biodiversity Network Species Dictionary (October 2002)
  2. Clapham, A. R., Tutin, T. G. & Moore, D. M. (1987) Flora of the British Isles. 3rd Ed. Cambridge University Press, Cambridge.
  3. UK Biodiversity Species Action Plan (October 2002):
  4. Preston, C. D. (1995) Pondweeds of Great Britain and Ireland. BSBI Handbook No. 8. Botanical Society of the British Isles, London.
  5. Hyam, R. and Pankhurst, R. (1995) Plants and their names. A concise dictionary. Oxford University Press, Oxford.
  6. Preston, C. D., Pearman, D. A. and Dines, T. D. (2002) New Atlas of the British and Irish Flora. Oxford University Press, Oxford.
  7. Stewart, A., Pearman, D. A. and Preston, C. D. (1994) Scarce plants in Britain. JNCC, Peterborough.