The aim of this paper is to validate the use of additive partitioning diversity models (species richness & Shannon index) and the mosaic landscape factors used in landscape ecology on the plant diversity present in the low-middle stretch of the Segre river. This model would be useful to evaluate the weight of exotic species within regional landscape diversity. The model implies that what we measure as within-community diversity at a higher scale level is the combined effect of heterogeneity at various lower levels. We have considered three different habitats integrated in the riparian ecosystem: the muddy line, the reed bed community and the riparian forest. In addition, we have partitioned the within and between diversity values depending on the chorology of the plants surveyed: native species and exotic species. The results show that the additive partitioning diversity model can be used in the riparian landscape despite of the proportions of the individual diversity components depending on the habitat type and the diversity aspect chosen. Nevertheless, the muddy line is the habitat that contains more exotic species. In the Segre river, the majority of the exotic species in the muddy line and the reed bed are agricultural weeds whereas ornamental plants are concentrated in the riparian forest.