The number of C4 plants living in Europe is increased to 120, and data on geographic origin, metabolic subtype, microecology and biotype, are given and compared with previous data. Our data agree with current ideas regarding the origin and biotype of the C4 plants, and only partially regarding ecology. At present, many C4 plants grow on disturbed sites or in stressed conditions, but ťhere is a lesser number of xerophytes than is currently thought and, conversely, some of them grow in favourable conditions. Among the latter mentioned, hydrophytic plants stand out because of their relatively great number and originality, as well as because no previous work on the ecology of C4 plants has indicated this.