S14 - Sparganium Erectum Swamp Sparganietum Erecti Roll 1938

Summary

Synonymy

Sparganium ramosum zone Walker 1905; Sparganium erectum society Spence 1964; Sparganium erectum reedswamp auct. angl.

Constant species

Sparganium erectum.

Rare species

Butomus umbellatus, Wolffia arrhiza.

Physiognomy

The Sparganietum erecti is generally dominated by Sparganium erectum which forms an open or closed cover of shoots about 1 m tall. Although pure and denser stands occur, there are usually some associates and certain of these can attain local prominence. The diversity and moderate species-richness of the vegetation are partly a reflection of the characteristic occurrence of the community in narrow open-water transitions where zonations are often contracted into jumbled mixtures but there are also some morphological and physiological features of the dominant which perhaps permit ready colonisation by other species. The underground organs of S. erectum comprises monopodial shoot-producing corms which, though bulky, are relatively short-lived (Cook 1961) and rhizomes which, though sometimes extensive, are much narrower than those of some other swamp dominants (Walker 1905, Cook 1961). The rather open and shifting network of buried organs and aerial shoots may thus leave patches of open water or substrate for invasion. Furthermore, although S. erectum thrives best in full sunlight (Cook 1961), it is shade-tolerant and will stand overtopping by other species, provided these are not too bulky. Indeed, elements of this community comprise one of the commonest synusial components of swamps under a variety of other dominants.

Sub-communities

Sparganium erectum sub-commuity. Here are included pure and very species-poor stands in which S. erectum is overwhelmingly dominant. There are sometimes floating or floating-leaved aquatics, notably duckweeds, on small areas of open water between the S. erectum shoots and Butomus umbellatus has been recorded in this vegetation.

Alisma plantago-aquatica sub-community. There may also be a patchy aquatic element in the more species-rich vegetation of this sub-community but the distinguishing feature is the occurrence, beneath and sometimes fronting the S. erectum, of an open and fragmentary understorey of species typical of shallow water margins, most frequently Alisma plantago-aquatica, sometimes with Callitriche stagnalis, Nasturtium officinale or Apium nodiflorum. Other swamp dominants, notably Typha angustifolia, and tall herbs such as Epilobium hirsutum or Urtica dioica may occur but these attain no more than local prominence, scattered plants or small clumps protruding above the bur-reed cover.