The Bonaerense Lower delta islands are formed by the accretion of silts transported and deposited by the Paraná river in the de la Plata river.
Unit B, downstream from A and locally referred to as forest nucleus, has a transitional hydrology between the fluvial influence of the Paraná river and the tidal influence of the de la Plata river.
Unit C forms the front of the delta and is subjected to direct influence of the tidal and eolic tides of the de la Plata river, which range from 1 to over 3 meters during strong southeastern winds.
The delta's accretion portion, where it grows by the deposition of sediments carried on the main rivers on their way to their mouth in the de la Plata river forming new islands and banks, constitutes Unit D.
The remaining species were mentioned as plant members of the Paraná river delta and the riverside of the de la Plata river by several authors (Hauman, 1923; Cabrera and Dawson, 1944; Cabrera, 1971, to name a few).
In addition, the tidal regime of the de la Plata river causes a bidirectional hydrological flow, which incorporates an additional hydric input and compensates for the seasonal drought characteristic of the Paraná river.