Species diversity has been of particular interest e.g. for nature conservation as well as human well-being. This study demonstrates the complex relationships between environmental conditions and species diversity. Against a theoretical background, it is the first study that represents various, partly interrelated phytodiversity relationships, in particular, in the context of coastal dune systems. Species diversity relationships are scale-dependent e.g. from global across regional to local scales, and in a hierarchical approach, various patterns and processes are highlighted.