Synonymy

Potamogeton pecrmöZws-Gesellschaft Oberdörfer 1977.

Constant species

Potamogeton pectinatus.

Physiognomy

The Potamogeton pectinatus community comprises species-poor vegetation dominated by this fine-leaved pondweed. It overwinters as fruits or small tuberous buds, but can make rapid growth in early summer to form bushy clumps, up to 2 m or so long and often very luxuriant, among which there are but few and typically only sparse associates. Small patches of duckweed thalli, with Lemna gibba and/or L. minor, are sometimes found floating above the stands in quieter waters, but submerged there are generally just scattered individuals of such plants as Callitriche stagnalis, Myriophyllum spicatum, Elodea canadensis and Ceratophyllum demersum with infrequent E. nuttallii, L. trisulca and Zannichellia palustris. In brackish water, the last can be joined by Ruppia spiralis and, in Scottish sea lochs, by Fucus ceranoides. Other Potamogeton spp. are rare, but P. perfoliatus has been recorded very occasionally.

Habitat

This kind of vegetation is characteristic of still to quite fast-moving, eutrophic waters, often with some measure of artificial enrichment, and frequently polluted and turbid. It is widespread through the warmer lowlands of Britain and has become increasingly common in pools and canals, dykes and streams as these have been contaminated by agricultural and industrial effluents and sewage.

P. pectinatus is a frequent plant through much of lowland England and the milder parts of the north and west, where the mean annual maximum temperature is for the most part above 25 °C (Conolly & Dahl 1970). Through these regions, it is characteristic of various kinds of aquatic vegetation in sites that are naturally rich in cations and nutrients, and sometimes attains the sort of overwhelming dominance typical of this community in such unpolluted situations. Vigorous stands can be found, for example, in clean, standing or sluggish -waters with clay or silt beds, habitats once common enough in the subdued scenery over softer, sedimentary rocks in the south and east of the country. But P. pectinatus seems especially well able to capitalise on the eutrophication that is now so widespread in our intensive agricultural landscapes and around settlements and industrial developments. It is also tolerant of various kinds of chemical pollution, indeed will actually grow more luxuriantly at certain levels of contamination with some effluents, provided the waters are not too fastmoving, shallow or very turbid (Haslam 1978).