The author discusses different life and growth form systems. Several of them are very complex, based on many criteria and difficult to apply in floristical and vegetational studies. The so-called dynamic systems are easier to apply and include several different simple systems each based on another criterium. Apart from this the life form systems can also be divided into phenotypical and genotypical systems. In a genotypical system the life forms depend on the genetic properties of the species, e.g. the ability to form rhizomes (e.g. the system of Warming; plants of the same species in different areas belong to the same life form), but in a phenotypical system the life forms depend also on the habitat of the plants (e.g. the system of Raunkiaer; plants of the same species in different areas can belong to different life forms). The first system is easier to apply than the second one. An important factor preventing immediate application of life form systems is that no Dutch flora mentions life forms and a few floras of other countries mention only the system of Raunkiaer. Within the framework of the study of Dutch dune slack vegetations the author devised and applied a dynamic genotypical system. It appeared that important results were obtained by making life form spectra for a number of successive years.