Floristic Provinces
A phytochorion, in phytogeography, is a geographic area with a relatively uniform composition of plant species. Adjacent phytochoria do not 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.
Read more about Floristic Provinces: Explanation, Floristic Kingdoms, Takhtajan's Floristic Provinces