information on the biology of species and the ecology of habitats found around the coasts and seas of the British Isles

Fennel pondweed (Stuckenia pectinata)

Distribution data supplied by the Ocean Biogeographic Information System (OBIS). To interrogate UK data visit the NBN Atlas.
Only coastal and marine records shown



A submerged aquatic pondweed characterized by many long narrow leaves. The leaves are 3 -11.5 cm long by only 0.2-4 mm wide, lack a stalk and are bright green to olive green in colour. Leaves are variable in shape and may be linear or thread-like, circular or grooved in cross-section, with 0-5 large and several small air channels bordering the midrib. Leaves taper to a fine point when narrow, or have rounded ends with a short point when broad. Stems are richly branched, slender or robust, circular in cross-section and up to 2.3 m in height. Leaves form a long (1-7cm), open leaf sheath where they meet the stems. Rhizomes are very slender or robust. Flowers born on tall bending stalks 2-9 (up to 28) cm long, in 2-7 groups of 1-2 flowers. Fruits egg-shaped 3-5 mm by 2-4 mm, with a short, curved beak, and pale brown in colour becoming brown with age.

Recorded distribution in Britain and Ireland

Widely distributed around the coasts of Britain and Ireland in brackish habitats but more common in inland waters (see Preston, 1995). Only coastal records are shown.

Global distribution

Near cosmopolitan in distribution occurring in Europe, North and South America, South Eurasia, South Africa and New Zealand.


Grows on sediments in still or flowing eutrophic fresh water in lakes, rivers, streams, canals, ditches, ponds, flooded sand and gravel pits, and in brackish water ditches and lagoons. The only Potamogeton species to occur in brackish water.

Depth range


Identifying features

  • Leaves narrow, many times longer than wide, with pointed tips.
  • Leaves bear air channels either side of an inconspicuous midrib.
  • Leaf sheaths open.
  • Floating leaves absent.
  • Stems circular in cross-section.
  • Flowers borne on long, bending stalk or peduncle up to 28 cm tall.
  • Carpels of flowers with a distinct style.
  • Fruits 3-5 mm long.

Additional information

Also known as sago pondweed. Potamogeton pectinatus is included in the subgenus Coleogeton (Preston, 1995). It may be confused with Potamogeton filiformis but is more branched, with finer leaves, open leaf sheaths and larger fruits. It may also hybridize with Potamogeton filiformis to form Potamogeton x suecicus, which is often mistaken for Potamogeton pectinatus (Preston, 1995).

Listed by

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Further information sources

Search on:


  1. Cronquist, A., 1988. The evolution and classification of flowering plants (2nd edn). New York: New York Botanical Garden.

  2. JNCC (Joint Nature Conservation Committee), 1999. Marine Environment Resource Mapping And Information Database (MERMAID): Marine Nature Conservation Review Survey Database. [on-line]

  3. Kantrud, H.A., 1990. Sago pondweed (Potamogeton pectinatus L.): a literature review. U.S. Fish & Wildlife Service, Fish & Wildlife Resource Publication no. 176, version 16 July 1997. [On-line], 2002-07-03

  4. National Biodiversity Network (NBN) Atlas website. Available from:  Accessed 01 April 2017

  5. Preston, C.D., 1995. Pondweeds of Great Britain and Ireland. London: Botanical Society of the British Isles. [B.S.B.I. Handbook no. 8.]

  6. Rose, F., 1981. The wild flower key. British Isles - N.W. Europe with keys to plants not in flower. London: The Penguin Group.

  7. Stace, C., 1999. Field flora of the British Isles. Cambridge: Cambridge University Press.


This review can be cited as:

Tyler-Walters, H., 2003. Stuckenia pectinata Fennel pondweed. In Tyler-Walters H. and Hiscock K. (eds) Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 18-08-2018]. Available from:

Last Updated: 11/08/2003