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Phytosociology is the study of the characteristics, classification, relationships, and distribution of plant communities. A phytosociological system is a system for classifying these communities. It is often suggested that it is not a Science in its formal sense.

The aim of phytosociology is to achieve a sufficient empirical model of vegetation using plant taxa combinations that characterize univocally vegetation units. Vegetation units as understood by phytosociologists may express largely abstract vegetation concepts (e.g. the set of all hard-leaved evergreen forests of western Mediterranean area) or actual readily recognizable vegetation types (e.g. cork-oak oceanic forests on Pleistocene dunes with dense canopy in SW-Iberian Peninsula). Such conceptual units are called "syntaxa" (singular "syntaxon") and can be set in a hierarchy system called "synsystem" or syntaxonomical system. The act of creation, amelioration or adjusting the synsystem is called "syntaxonomy". Therefore, the syntaxonomical system is putatively a sufficient empirical representation of vegetation of a given territory. An International Code of Phytosociological Nomenclature, issuing the rules for naming ‘‘syntaxa’’ exists and its use has increased among vegetation scientists.

The basic unit of syntaxonomy is the "association". The association is a conceptual model of a concrete phytocenosis (the plant component of a biocoenosis). The association is defined by its characteristic combination of plant taxa, habitat features, physiognomy, biogeographical area, role in ecological succession, historical (e.g. history of use by humans) and paleo-biogeographical relationships. Associations with floristic and territorial affinities can be grouped in larger ecological conceptual units (i.e. syntaxa) called "alliances". Similar alliances may be grouped in "orders" and orders in vegetation "classes". The setting of syntaxa in such a hierarchy makes up the syntaxonomical system, or the reference model of the given vegetation and territory.

In spite of early attempts (e.g. Charles Flauhault in the late XIX century), this science started in Europe, with the Swiss botanist and ecologist Josias Braun-Blanquet (1884 - 1980).

Nowadays, Phytosociology try to develop to include higher levels of complexity in the perception of vegetation, namely by describing whole succesional units (vegetation series) or, in general, vegetation complexes. These lie in the scope of Landscape Phytosociology. Other developments include the use of multivariate statistics for the definition of syntaxa and their environmental interpretation.

On one hand, some authors consider that Phytosociology is in the scope of contemporary Vegetation Science, as a successful approach because of its high descriptive and predictive power, and its use in Nature Management issues. In the other hand, there are numerous critics that are focusing several methodological limitations: the absence of statistical approaches, the complexity and non-stability of the nomenclatural system, the mistakes in the predictive models, and the assumption of several concepts that are in the basis of the theory.

Even if in continental Europe, a complete synsystem describing vegetation types has been developed and it is a basis for habitat-type classification (e.g. NATURA 2000 typology and habitat network), there are numerous scientific experts that do not inform positively about the suitability to be the main geobotanical approach to manage our vegetation systems. An important point of disagreement is the floristic-phytosociological assumption considering that the forest patches the Mediterranean species of pines mainly derived from afforestations, non-stables and incidental.

• Landscape disagreement with phytosociological theories
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