A15 - Elodea Canadensis Community Elodea Nuttallii in Aquatic Vegetation

Summary

Synonymy

Elodetum Matthews 1914, Tansley 1939; Mediumslow current vegetation Butcher 1933 p.p.; Pflanzengesellschaft mit Elodea canadensis Solinska 1963; Elodeetum canadensis (Pignatti 1953) Passarge 1964; Elodea society Spence 1964.

Constant species

Elodea canadensis.

Physiognomy

The Elodea canadensis community comprises speciespoor vegetation in which this particular kind of North American pondweed has become dominant. The plant overwinters as short unbranched stems or as turions but, by early summer, it can become very abundant, either as free-floating masses or with the shoots rather loosely anchored in the substrate. In such stands, other species are at most only occasional, though quite a variety are represented at low frequency. Commonest among other submerged aquatics are Ceratophyllum demersum, Myriophyllum spicatum, Potamogeton pectinatus, P. crispus, P. perfoliatus, Callitriche stagnalis, C. hamulata, Ranunculus circinatus and R. penicillatus ssp. pseudofluitans. Then, there are quite often some associated mats of duckweeds Lemna minor and L. gibba, with Potamogeton natans and Polygonum amphibium forming an open canopy of floating leaves. Glyceria fluitans shoots sometimes trail in from water margins.

Habitat

The Elodea canadensis community is most characteristic of still to sluggish, nutrient-rich waters, shallow to quite deep, and generally with fine mineral beds. Since the introduction of the plant, some century and a half a go, it has become very widespread through the warmer lowlands of Britain, occurring commonly in ponds and lakes, canals, dykes and slow-moving rivers and streams. Although its overall range seems to have now stabilised, E. canadensis will still actively colonise new water bodies, and the community often makes an early appearance in sites like flooded gravel pits, as well as sometimes quickly returning to waters recovering from pollution.

E. canadensis is native to most of the United States and parts of Canada and was first authentically reported from Great Britain in 1842, having perhaps been introduced on imported timber. Its period of rapid spread started shortly after 1850, when it began to appear in abundance around the Fens, and within a decade it was to be found in most of southern England and parts of the Midlands, extending through nearly all of the English lowlands and into some of southern Scotland by 1880.