What is “Phytochorion” ?
A phytochorion, in phytogeography, is a geographic area with a relatively uniform composition of plant species. Adjacent phytochoria don’t usually have a sharp boundary, but rather a soft one, a transitional area in which many species from both regions overlap. The region of overlap is called a vegetation tension zone.
Several systems of classifying geographic areas where plants grow have been devised. Most systems are organized hierarchically, with the largest units subdivided into smaller geographic areas, which are composed of smaller floristic communities, and so on. Phytochoria are defined as areas possessing a large number of endemic taxons. Floristic kingdoms are characterized by a high degree of family endemism, floristic regions by a high degree of generic endemism, and floristic provinces by a high degree of species endemism. Systems of phytochoria have both significant similarities and differences with zoogeographic provinces, which follow the composition of mammal families, and with biogeographical provinces or terrestrial ecoregions, which take into account both plant and animal species.
The term phytochorion is especially associated with the classifications according to the methodology of Josias Braun-Blanquet, which is tied to the presence or absence of particular species.
Taxonomic databases tend to be organized in ways which approximate floristic provinces, but which are more closely aligned to political boundaries, for example according to the World Geographical Scheme for Recording Plant Distributions.
Botanist Ronald Good identified six floristic kingdoms, the largest natural units he determined for flowering plants. Good’s six kingdoms are subdivided into smaller units, called provinces. The Paleotropical kingdom is divided into three subkingdoms, which are each subdivided into floristic provinces. Each of the other five kingdoms are subdivided directly into provinces. There is a total of 37 floristic provinces. Almost all provinces are further subdivided into floristic regions.
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