The main goal of this research was to determine the distribution of genus Forsythia Vahl species and variability among them in Slovenia. Determination keys of Forsythia genus are numerous, but not all are appropriate for our analysis, because they do not contain all the species which occur in Europe, they also do not have unified entrances or they are simply not accurate enough. To avoid the deviations and determination of different species we decided to use the key with the highest number of described species and the most accurate entrances. With the Gehölze determination key we did not manage to determine variability within Forsythia Vahl genus species in Slovenia. We confirmed the presence of Forsythia * intermedia species, and its numerous types. The presence of the other species could not have been confirmed. Morphological analysis of the leaves verified a significant difference among leaves growing on the northern and southern side of the bush. With PCA analysis the differences could not have been proved. The differences in the specimens from Ljubljana, Kranj and Postojna may be due to clonal reproductionof Forsythia with clones originating from the same local tree nurseries.