Pondweeds grow in many environments

On the Finnish coastline, pondweeds are probably the most well-known aquatic vascular plants in the sea. They grow in both clear and turbid waters, and on soft- and mixed-sediment bottoms. Provided other conditions are favourable, even a surprisingly small patch of soft sediment is enough to support pondweed growth.

Pondweeds often tangle fishing lures, fishhooks and boat propellers, as well as tickle swimmer's feet and belly. In shallow coastal communities, they are invaluable because they:

  • anchor bottom sediment, keeping it in place
  • bind available nutrients in the water
  • photosynthesize and produce oxygen in the water
  • form protective structures as they grow, which provide shelter for fish and various invertebrates
  • provide a source of food for many small plant-eating grazer species

Pondweeds can be divided into two genera

Pondweeds comprise a broad and diverse group of plants which are now divided into two genera, i.e. Stuckenia and Potamogeton. Pondweeds can be found along the entire coastline, from the almost freshwater ponds of the inner archipelago to the open sandy beaches of the outer archipelago.

Many pondweed species are familiar to summer-cottage owners and boaters

In Finland, the most common species are the fennel- (Stuckenia pectinata) and the perfoliate pondweed (Potamogeton perfoliatus). Both species thrive in all kinds of environments and salt levels and are not particularly sensitive to eutrophication. There are also more demanding and sensitive species among the pondweeds, such as the now much-diminished flat-stalked pondweed, i.e. Potamogeton friesii.

The curled shoots of the fennel pondweed, i.e. Stuckenia pectinata, are familiar on almost every summer-cottage shore. Shoots may reach up to one and a half metres in length and these plants can grow either as individuals or in an extensive monoculture or a mixed community with other vascular plants. Stuckenia has several similar-looking relatives, the most common of which is the threadleaf pondweed (S. filiformis), which favours more open spaces, and the sheathed pondweed (S. vaginata) which is particularly common in the Bay of Bothnia.

The oval leaves of the perfoliate pondweed, i.e. Potamogeton perfoliatus, clasp around the stem, which can grow to more than two metres in length. Although the appearance of this pondweed species can vary widely depending on the habitat, the characteristic leaves with their long stripes help to distinguish it from the diverse range of other pondweeds. The perfoliate pondweed is one of Finland's most recognisable aquatic plants and is certainly familiar to both boaters and anglers alike.

 Vascular plant Potamogeton's leaf structure can be seen in clear water
Perfoliate pondweed is a familiar site along summer-cottage shores and in shallow bays.

Pondweed species

  • Fennel or Sago pondweed (Stuckenia pectinata)
  • Perfoliate pondweed (Potamogeton perfoliatus)
  • Flat-stalked pondweed (Potamogeton friesii)
  • Threadleaf (Stuckenia filiformis)
  • Sheathed pondweed (Stuckenia vaginata)