Forests dominated by Salix neotricha, and Populus alba found along the mesoeutrophic rivers in the Iberian Peninsula, were
studied. We discuss the floristic circumscription, chorology, and community segregation based on the available releve´s of all
Iberian riparian communities included in Populenion albae. Eleven formerly described communities were analyzed and due to
original floristic combination, habitat features, and biogeographic scope, a new willow and poplar forest type is proposed
within a well-defined biogeographical unit (Sadensean-Dividing Portuguese Subprovince): Clematido campaniflorae-
Salicetum neotrichae. This syntaxon is found under a semi-hyperoceanic thermomediterranean to lower mesomediterranean,
subhumid to humid bioclimate. Cluster analysis including all Iberian communities of Populenion albae shows a clear floristic
segregation within the suballiance and confirms the originality of the new association. Furthermore, chemical characteristics
of the water along some of the Portuguese watercourses with Populenion albae were studied and compared to the oligotrophic
rivers occupied by Osmundo-Alnion communities. This study suggests that floristic separation between the communities of
Populenion and Osmundo-Alnion is accompanied by a differentiation of the water trophic level
