The results of mapping of grasses (Poaceae) from open and disturbed sites in South Tyrol are presented. The aim of mapping was to check the presence of species in the mentioned sites and to note their limits in horizontal and altitudinal distribution as well as their chorological status. The data is meant to be a basis for future comparative investigations. In total, 49 species and subspecies are treated. By comparing the results with distribution data from the literature it turns out that in the course of the20th century the following species, which are established for a long time, have spread along the main valleys: Cynodon dactylon, Digitaria sanguinalis, Echinochloa crus-galli, Eragrostis minor, and E. pilosa. The same goes for Eleusine indica, Panicum capillare, and Sorghum halepense, species which first emerged in South Tyrol only in the second half of the 20th century. A significant extension in vertical distribution is reported for Echinochloa crus-galli, Eragrostis minor, and E. pilosa. Dispersal vectors as well as possible causes of the extension of horizontal and vertical limits and, in some species, of decline are discussed. The behaviour of Cynodon dactylon provides an indication of increasing altitudinal distribution, possibly caused by elevated temperatures.