The most relevant problems in plant taxonomy and geography for which numerical taxonomy is used are briefly discussed. The attention is focused to the problems of geographic variation within species and clinal variations in respect to ecological factors. Examples of applications to morphological data ofEuphrasiaproved the existence of a clear geographical pattern of variation withinE. minimawhich shows a decrement of sharpness of the leaves teeth along an East-West gradient and along an elevation gradient. The pattern of distribution of Italian species ofEuphrasiain respect to three factors—light, elevation and soil drainage—reflects very well the ordination and the classification obtained by numerical methods based on morphological characters. A software for phytogeographic data is illustrated with an example of application to a floristic data bank of the Italian Karst region. It allows to cluster geographic units and to define the discriminating species at different hierarchical levels.