Synonymy

Rorippa islandica-Gnaphalium uliginosum community Birse 1984.

Constant species

Filaginella uliginosa, Rorippa palustris.

Rare species

Limosella aquatica.

Physiognomy

The Rorippa palustris-Filaginella community comprises open or closed vegetation in which R. palustris and Filaginella uliginosa are the most consistent feature and where either can be abundant over patches of damp mud, but which may also be variously dominated by the occasional to frequent annual knotweeds, Polygonum persicaria, P. hydropiper and P. aviculare. Bidens tripartita also occurs commonly but not usually with any abundance and there is usually some Juncus bufonius. Other plants recorded occasionally are Plantago major, Lythrum portula, Littorella uniflora and the grasses Agrostis stolonifera, Alopecurus geniculatus, Poa annua and Phalaris arundinacea. Scattered individuals of Rumex crispus, R. obtusifolius, Chenopodium rubrum, Cirsium arvense and Epilobium obscurum may catch the eye but such species are never common. This community can provide a locus for the nationally rare Limosella aquatica.

Habitat

The Rorippa-Filaginella community is characteristically found in periodically-flooded, eutrophic muds and sands around the margins of fluctuating pools, lakes and reservoirs, on islands and banksides in mature river systems and in ruts along paths and trackways.

The community depends upon the exposure of bare, damp substrates by lowering of water-tables in rivers and lakes after the winter or by evaporation from smaller pools and flooded ruts with the warmth of spring.