Vascular plant communities occupying gravel deposits of rivers, including pioneer vegetation and subsequent stages in the colonization sequence. Early-stage communities of Alpide, boreal and Mediterranean watercourses are specialised, those of nemoral lowlands and hills are related to other formations, in particular those of unit E3. Vegetation communites of e.g. Thlaspietea rotundifolii - Glaucion flavi and Salicion eleagno-daphnoidis, with the most typical species Caltha palustris ssp. laeta, Salix elaeagnos, Salix purpurea and Poa trivialis.