Synonymy

Scirpeto-Phragmitetum medioeuropeaum (Koch 1926) R.Tx. 1941 p.p.; Gemeenschap van Acorus calamus en Iris pseudacorus Olivier & Segal 1963 p.p..

Constant species

Acorus calamus.

Rare species

Crassula helmsii.

Physiognomy

The Acoretum calami comprises stands dominated by Acorus calamus forming an open or closed cover of leafy shoots up to about 1 m tall.

Sub-communities

Acorus calamus sub-community. Here are included pure or very species-poor stands of dense Acorus.

Lemna minor sub-community. In this sub-community, a generally shorter and more open cover of the dominant emerges from open water with a sometimes abundant mat of floating Lemna minor. Other swamp dominants such as Typha latifolia and Sparganium erectum may attain local prominence and there are sometimes tussocks of Juncus effusus and sprawls of Solanum dulcamara and Galium palustre. Tall herbs like Angelica sylvestris, Lycopus europaeus and Rumex hydrolapathum occur occasionally and a wide variety of other water margin species are represented rarely. The introduced Australasian water-plant Crassula helmsii (e.g. Clement 1979) has been recorded here.

Habitat

The community occurs in standing or slow-moving waters, 20-80 cm deep, or more rarely on the waterlogged margins, of ornamental pools, ponds, canals and dykes. The substrate is usually silt or clay and pH values of 5.4-7.2 have been recorded.

Zonation and succession

Acorus was introduced into Britain, probably before 1660 (Salisbury 1964) and for the medicinal value of its underground organs (Haslam 1978). It was planted thereafter as an ornamental and its sweet-smelling leaves have been used for strewing in churches (Salisbury 1964, Ellis 1965). Isolated stands in ornamental pools often represent deliberate plants but, although seed is not produced in Europe, Acorus spreads well by vegetative means and the Lemna sub-community perhaps includes stands of natural swamp and marginal vegetation which have been invaded.

Distribution

Acorus occurs in scattered localities throughout the English lowlands with concentrations in Lancashire, the central Midlands and the London Basin.

Affinities

Swamp dominated by Acorus has hardly been mentioned in accounts of British vegetation, although a similar community has been describèd from The Netherlands (Westhoff & den Held 1969). The ecological amplitude of the species in Europe places the Acoretum alongside shallow-water swamps of mesotrophic mineral substrates such as the Sparganietum erecti and Typhetum latifoliae.