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Aim To establish the relationship between coastal dune vegetation and its pollen representation as an aid to interpret Holocene vegetation dynamics and environmental changes from pollen assemblages.

Location The study area is situated on the temperate Atlantic coast of south Buenos Aires Province, Argentina (c. 39° S and 61°20′ W).

Methods The vegetation of the active dune area adjacent to the beach was described on the basis of its floristic composition from 25 plots. Classification of the vegetation into distinct zones was carried out by cluster analysis. Surface samples were collected from each vegetation stand and analysed for their pollen composition. Pollen percentage data were analysed using principal components analysis in order to investigate the degree to which the different vegetation units can be distinguished by their pollen spectra. Pollen–vegetation relationships for selected taxa were explored using simple scatter plots and indices of association, under- and over-representation. Indices of floristic diversity and palynological richness were used to assess the representation of the vegetation in the pollen spectra.

Results and conclusions Five vegetation zones are defined on the basis of species composition and their quantitative variation: back shore, mobile dunes, slacks, semi-fixed and fixed dunes. Pollen assemblages from back shore, mobile dunes and slacks are clearly differentiated from semi-fixed and fixed dunes. Pollen assemblages differ considerably from the associated vegetation composition. Major discrepancies are caused by large differences in pollen and vegetation proportion of Hyalis argentea and Discaria americana. There is a considerable proportion of non-local pollen in every spectrum. Pollen representation in the coastal dunes at Monte Hermoso is influenced by differences in pollen production, dispersal and preservation of individual taxa as well as by the spatial distribution of the vegetation, the topography of the dune system and the wind pattern. The pollen–vegetation relationship established in this study has important implication for understanding and interpreting fossil pollen records from coastal dune environments.

Amphicypris argentinensis sp. nov., is described and illustrated from Laguna Caliba, an ephemeral fresh water lake from the southern coast of Buenos Aires Province, Argentina. Specimens were raised from dried sediment recovered from a bank of ostracod shells found at the edges of the lake. Deposition of progressively smaller ostracod valves stacked one into another (cup-in-cup structure) is documented. The geographical distribution and ecology of the genus is briefly discussed.