In continuation of a former study on the ‘Elevation Effect’ in the Swiss mountain flora (Backhuys, 1968), the distribution of six Taraxacum species in Switzerland was examined in detail. This was enabled by the preceding monographic study by J. L. van Soest (1969). The interesting point was to compare species of one genus with a common dispersal mechanism. Data on the vertical distribution are provided in table I and diagrams 1—6. It was found that all six species show an elevation effect which varies from 200—750 m. In five species this range is as narrow as 500—750 m. See table II. It is concluded that in spite of the very obvious dispersal mechanism (parachute-achenes) the species are apparently not capable to colonise ‘mountain islands’ the summit altitude of which is situated between the lowest known locality and the lowest mountain island on which the species concerned is found. These data support the view that the elevation effect is a plant-geographical rule of universal validity for mountain plants.