OV29: Alopecurus geniculatus-Rorippa palustris community: Ranunculo-Alopecuretum geniculati R.Tx. (1937) 1950

Summary

Constant species

Alopecurus geniculatus, Rorippa palustris.

Physiognomy

A mat of Alopecurus geniculatus, often extensive and lush, is the most distinctive characteristic of the Ranunculo-Alopecuretum, with sometimes a small contribution to the carpet from Potentilla anserina, Poa trivialis and Ranunculus repens. There are frequent scattered plants of Rorippa palustris and various annual knotweeds, among which Polygonum lapathifolium, P. aviculare and P. hydropiper are the most common. Rumex crispus also occurs often and there can be some Elymus repens and Phalaris arundinacea, though these are generally not very abundant. A wide range of plants of damp, weedy places occur at low frequency.

Habitat

The Ranunculo-Alopecuretum is typical of periodically-flooded sills and sands on terraces, bars and islands in mature river valleys, on the edges of seasonal pools and small gentle streams in the lowlands and around fluctuating ponds and lakes with more nutrient-rich waters. Modest trampling by people, stock or wildfowl can be important in maintaining open ground for this vegetation and for dispersal of propagules.

Flooding by river or lake waters or the seasonal accumulation of rainwater in shallow depressions can handicap the growth of pasture vegetation or leave deposits of silt and sand around shores and on the terraces of river valleys. Then the species of this community are often able to take rapid advantage of the areas of bare ground thus created, by germination of seed and spread of vegetative propagules.