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The δC values of submerged aquatic plants from contrasting but relatively defined habitats, and the δC values of emergent, floating and submerged leaves of dimorphic aquatic plants, were measured. In many instances the δC values of dissolved inorganic carbon in the water were also measured. Plant δC values in the vicinity of-40 to-50‰ were found in rapidly flowing spring waters with carbonate δC values of-16 to-21‰, consistent with the notion that species such as Fontinalis antipyretica almost exclusively assimilate free CO via RuP carboxylase. Plant δC values in the vicinity of-10 to-15‰ in sluggish water with carbonate δC values of about-5‰ were observed, consistent with the notion that boundary layer diffusion and/or HCO uptake may determine the δC value of submerged aquatic plants in these circumstances. Comparisons of δC values of the same or related species growing in waters of similar carbonate δC value but different flow rates confirmed this view; more negative δC values were frequently associated with plants in fast moving water. In Britain, but not in Finland, the δC values of submerged leaves of dimorphic plants were almost invariably more negative than in aerial leaves. The δC value of carbonate from chalk streams and in acid springs indicate substantial inputs of respiratory CO, as opposed to atmospheric carbon. The contributions of these variations in δC of the carbon source, and of isotope fractionation in diffusion, to the δC value of submerged parts of dimorphic plants is discussed.

Aim  To identify floristic elements in the European flora by an analysis of the distributions of species and species groups mapped in Atlas Florae Europaeae. Location  Europe, as defined by Flora Europaea. Methods  We analysed the native distributions of 2762 species and 33 species’ aggregates from 79 families, which represent c. 20% of the European flora. The distributional data base, derived from Atlas Florae Europaeae, includes records from 4420 50 × 50‐km UTM grid squares. We classified species into floristic elements by a three‐stage clustering procedure, which consisted of: (1) constructing a dissimilarity hierarchy by complete linkage clustering, using a distance measure based on Jaccard’s coefficient; (2) cutting the hierarchical tree at the 0.95 level to create initial clusters, and forcing small clusters to link with larger ones until the sum of within‐group pairwise distances exceeded a threshold value; and (3) checking the allocation of all species to the redefined clusters and reassigning species if appropriate, using the cosine of the angle between the species and cluster centres to measure the similarity of species to clusters. Results  The clustering procedure classified 2793 taxa into 18 floristic elements, which included between 66 and 289 taxa; two species had unique, non‐overlapping distributions and could not be classified. Main conclusions  The analysis highlights the floristic diversity of the mountains of central and southern Europe, and of the Mediterranean region. The floristic elements of northern latitudes and the temperate lowlands tend to be composed of wide‐ranging species and include only a low proportion of European endemics. The montane elements, including those centred on montane areas in the Mediterranean region, are composed predominantly of perennial species and include high or very high proportions of European endemics. Classifications that recognize one ‘Alpine’ and one ‘Mediterranean’ biogeographical zone in Europe fail to reflect this floristic diversity.

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