To interpret this map it is necessary to know that detailed distribution data were available for some countries (such as Spain, France and Fennoscandia) whereas for others the only data available were presence or absence at a national level and therefore the map was created by selecting the whole country (Balkan states and Central and East Europe). This gives a false impression of a high density over very large areas in the centre and southeast of Europe.
In fact, the top five EU countries in terms of aquatic plant species richness (in descending order) are: France, Italy, Spain, Germany and Poland. It is notable, that most aquatic plants have a very wide distribution, occurring in a large number of countries. Of the 27 EU countries only seven support fewer than 200 species and the main correlation appears to be that south of Fennoscandia, it is the size of the country that has the greatest influence over the number of aquatic species which a country supports. Of the 395 species assessed, 38 are found in only one country, of which 17 (45%) belong to genera known to have taxonomic problems; Isoetes, Trapa or Zannichellia many of which may, in time, be shown to simply be forms of other taxa; 24 occur in two countries; 307 (approximately three quarters) occur in five or more countries and 197 (approximately half) occur in 20 or more countries.
The distribution of endemic aquatic plants shows that there is a high rate of endemism in the north and west of the Iberian Peninsula, central and northern France, Belgium and the Netherlands with the UK, Germany and Denmark as well as Ukraine and Russia. Regarding the size of the areas covered by endemic species, the same caveat as above applies.
Of the 26 threatened aquatic plant species, most are found in the Atlantic region, the Iberian Peninsula and other parts of the Mediterranean, with only a few occurring in northern countries. Six threatened species are endemic to the Iberian Peninsula and two threatened species are endemic to the Azores. Fourteen threatened species can be considered predominantly Mediterranean in distribution. The concentration of threatened aquatic plants in the Iberian Peninsula and the Mediterranean is more a consequence of the combination of the high diversity of threatened plants, particularly endemic species, and the distribution of the most vulnerable habitat types, mainly ephemeral pools. Only four threatened species have a predominantly northern distribution. Lythrum thesioides has a curious distribution, occurring in France, Italy, Hungary and Russia. It seems likely that the major gaps in its distribution must be due to under-recording or taxonomic confusion.