Due to their complexity, vegetation phenomena are not understandable without
a consistent conceptual framework. A few indispensable concepts to explore the
northeastern Portuguese ultramafic vegetation are set out in Tables 9 and 10. Association. The Phytosociology fundamental abstract unit is the association or associatio.
The concept of association comprises an ecological-taxonomic model of the reality.
Therefore, the association includes the notion of a plant community (biological information:
floristic, physiognomic etc.) that occupies a particular biotope (chorologic
information) where a specific set of environmental conditions can be found, i.e. the
habitat (environmental information). The taxonomic element is mainly supported on
the floristic composition, which is characteristic and statistically constant between
associations. The development of a hierarchical syntaxonomic system (synsystem) is
based above all on floristic, but also on environmental, biogeographic and physiognomic
characters. Although the association concept is not a true synonym of phytocoenosis
the two terms are often used interchangeably, which may result abusive
