Phytochorion


In phytogeography, a phytochorion 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, called a vegetation tension zone.
In traditional schemes, areas in phytogeography are classified hierarchically, according to the presence of endemic families, genera or species, e.g., in floral 'zones and regions, or also in kingdoms, regions and provinces, sometimes including the categories empire and domain'. However, some authors prefer not to rank areas, referring to them simply as "areas", "regions" or "phytochoria".
Systems used to classify vegetation can be divided in two major groups: those that use physiognomic-environmental parameters and characteristics and those that are based on floristic relationships. Phytochoria are defined by their plant taxonomic composition, while other schemes of regionalization may variably take in account, depending on the author, the apparent characteristics of a community, environment characteristics, the fauna associated, anthropic factors or political-conservationist issues.

Explanation

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 made up of smaller floristic communities, and so on. Phytochoria are defined as areas possessing a large number of endemic taxa. 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, mainly in Africa.
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.

Early schemes

In the late 19th century, Adolf Engler was the first to make a world map with the limits of distribution of floras, with four major floral regions. His Syllabus der Pflanzenfamilien, from the third edition onwards, also included a sketch of the division of the earth into floral regions.
Other important early works on floristics includes Augustin de Candolle, Schouw, Alphonse de Candolle, Drude, Diels, and Rikli.

Good (1947) regionalization

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 regions and provinces. The Paleotropical kingdom is divided into three subkingdoms, which are each subdivided into floristic regions. Each of the other five kingdoms are subdivided directly into regions. There are a total of 37 floristic regions. Almost all regions are further subdivided into floristic provinces.

Takhtajan (1978, 1986) regionalization

, in a widely used scheme that builds on Good's work, identified thirty-five floristic regions, each of which is subdivided into floristic provinces, of which there are 152 in all.

[Holarctic kingdom]

I. [Circumboreal region]

II. [Eastern Asiatic region]

III. [North American Atlantic region]

IV. Rocky Mountain region">Rocky Mountain floristic region">Rocky Mountain region

V. Macaronesian region">Macaronesia">Macaronesian region

VI. [Mediterranean region]

VII. [Saharo-Arabian region]

VIII. [Irano-Turanian region]

8A. Western Asiatic subregion
8B. Central Asiatic subregion

IX. [Madrean region]

[Paleotropical kingdom]

X. [Guineo-Congolian region]

XI. [Usambara-Zululand region]

XII. [Sudano-Zambezian region]

12A. Zambezian subregion
12B. Sahelo–Sudanian subregion
12C. Eritreo–Arabian subregion
12C. Omano-Sindian subregion

XIII. [Karoo-Namib region]

XIV. [St. Helena and Ascension region]

XV. [Madagascan region]

XVI. [Indian region]

XVII. [Indochinese region]

XVIII. Malesian region">Malesia">Malesian region

18A. Malesian subregion
18B. Papuan subregion

XIX. [Fijian region]

XX. [Polynesian region]

XXI. Hawaiian region">Hawaiian Islands">Hawaiian region

XXII. Neocaledonian region">New Caledonia">Neocaledonian region

Neotropical kingdom">Neotropic">Neotropical kingdom

XXIII. Caribbean region

XXIV. [Region of the Guayana Highlands]

XXV. [Amazon region]

XXVI. [Brazilian region]

XXVII. Andean region

[South African kingdom]

XXVIII. Cape region">Cape floristic region">Cape region

[Australian kingdom]

XXIX. [Northeast Australian region]

XXX. Southwest Australian region">Southwest Australia">Southwest Australian region

XXXI. Central Australian or Eremaean region">Eremaean province">Eremaean region

Antarctic kingdom">Antarctic Floristic Kingdom">Antarctic kingdom

XXXII. Fernandezian region">Juan Fernández Islands">Fernandezian region

XXXIII. [Chile-Patagonian region]

XXXIV. [Region of the South Subantarctic Islands]

XXXV. [Neozeylandic region]

Regionalization according to Wolfgang Frey and Rainer Lösch (2004, 2010)

;Notes:
  • The central European region and the central Russian region are sister regions.
  • The border between them is similar to the Fagus sylvatica limit.
  • The border between the central Russian region and the boreal region is similar to the Quercus spp. limit.
  • The border between the boreal region and the arctic region is similar to the tree line, taiga/arctic tundra limit.
  • The border of the Atlantic region is the limit of no frost, Gulf Stream influence.
  • The warm islands in the Atlantic Ocean are in the Macaronesia region: isolated populations in a more humid environment.
  • The Mediterranean region is similar to the occurrence of wild Olea europea and wild Cistus salviifolius.
  • The border between the submediterranean region and the central European region is similar to the alpine arc, a weather barrier.
  • The Pontic region border is similar to the tree line/ steppe limit.
  • The Turanian region has a semi-arid climate.

    Liu ''et al.'' (2023, 2024) Regionalization

Critiquing previous attempts for their lack of phylogenetic relationships in the construction of their regions, Liu et al. incorporated distribution data alongside phylogenetic relationships to configure their realms. This led to the classification of eight realms organized into two super-realms and each composed of a number of sub-realms.
  • Gondwanan super-realm
  • Laurasian super-realm
Differences from Takhtajan's floristic kingdoms mainly focus on emphasizing the uniqueness of certain realms that he had as subdivisions within kingdoms. Two examples are separating some kingdoms into two separate realms, as happened to the Paleotropical and Antarctic kingdoms, reasoning that they have been separated form each other for long enough time to constitute a different phylogenetic trajectory. The merging of the Cape floristic kingdom with the African realm was based by the low endemism of higher taxonomic ranks, which could be found outside the cape region in the rest of Africa. The final major change is the separation of the Saharo-Arabian realm from the Holarctic kingdom, though they admit the northern boundary is not clear, with flora from the Holarctic being found within this area.
After publishing their regions, Dr. Hong Qian criticized Liu et al. for the inclusion of nonnative distributions in their analyses. In response to this, the group cleaned their data to remove nonnative ranges and reassessed their regions. They suggest that the previous inclusion of exotic species did not significantly affect their mapping and found that the cleaned data revealed the same floristic realms.