# Phytochorion

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.
In traditional schemes, areas in phytogeography are classified hierarchically, according to the presence of endemic families, genera or species, e.g., in floral (or floristic, phytogeographic) 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" (in a non hierarchical sense) 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 (i.e. shared genera and species) relationships. Phytochoria are defined by their plant taxonomic composition, while other schemes of regionalization (e.g., vegetation type, physiognomy, plant formations, biomes) may variably take in account, depending on the author, the apparent characteristics of a community (the dominant life-form), 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" (Werger & van Gils, 1976) 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 (1844-1930) was the first to make a world map with the limits of distribution of floras, with four major floral regions (realms). His Syllabus der Pflanzenfamilien, from the third edition (1903) onwards, also included a sketch of the division of the earth into floral regions.
Other important early works on floristics includes Augustin de Candolle (1820), Schouw (1823), Alphonse de Candolle (1855), Drude (1890), Diels (1908), and Rikli (1913).

## Good (1947) regionalization

Botanist Ronald Good (1947) identified six floristic kingdoms (Boreal or Holarctic, Neotropical, Paleotropical, South African, Australian, and Antarctic), 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

Armen Takhtajan (1978, 1986), 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

    1 Arctic province
    2 Atlantic Europe province
    3 Central Europe province
    4 Illyria or Balkan province
    5 Pontus Euxinus province
    6 Caucasus province
    7 Eastern Europe province
    8 Northern Europe province
    9 Western Siberia province
    10 Altai-Sayan province
    11 Central Siberia province
    12 Transbaikalia province
    13 Northeastern Siberia province
    14 Okhotsk-Kamchatka province
    15 Canada incl. Great Lakes province

#### II. Eastern Asiatic region

    16 Manchuria province
    17 Sakhalin-Hokkaidō province
    18 Japan-Korea province
    19 Volcano-Bonin province
    20 Ryūkyū or Tokara-Okinawa province
    21 Taiwan province
    22 Northern China province
    23 Central China province
    24 Southeastern China province
    25 Sikang-Yuennan province
    26 Northern Burma province
    27 Eastern Himalaya province
    28 Khasi-Manipur province

#### III. North American Atlantic region

    29 Appalachian province (forested areas extending east to include the piedmont and west to the start of the prairies)
    30 Atlantic and Gulf Coastal Plain province
    31 North American Prairies province

#### IV. Rocky Mountain region

    32 Vancouverian province
    33 Rocky Mountains province

#### V. Macaronesian region

    34 Azores province
    35 Madeira province
    36 Canaries province
    37 Cape Verde province

#### VI. Mediterranean region

    38 Southern Morocco province
    39 Southwestern Mediterranean province
    40 South Mediterranean province
    41 Iberia province
    42 Baleares province
    43 Liguria-Tyrrhenia province
    44 Adriatic province
    45 East Mediterranean province
    46 Crimea-Novorossijsk province

#### VII. Saharo-Arabian region

    47 Sahara province
    48 Egypt-Arabia province

#### VIII. Irano-Turanian region
##### 8A. Western Asiatic subregion

    49 Mesopotamia province
    50 Central Anatolia province
    51 Armenia-Iran province
    52 Hyrcania province
    53 Turania or Aralo-Caspia province
    54 Turkestan province
    55 Northern Baluchistan province
    56 Western Himalaya province

##### 8B. Central Asiatic subregion

    57 Central Tien Shan province
    58 Dzungaria-Tien Shan province
    59 Mongolia province
    60 Tibet province

#### IX. Madrean region

    61 Great Basin province
    62 Californian province
    63 Sonoran province
    64 Mexican Highlands province

### Paleotropical kingdom
#### X. Guineo-Congolian region

    65 Upper Guinean forests province
    66 Nigeria-Cameroon province
    67 Congo province

#### XI. Usambara-Zululand region

    68 Zanzibar-Inhambane province
    69 Tongoland-Pondoland province

#### XII. Sudano-Zambezian region
##### 12A. Zambezian subregion

    70 Zambezi province

##### 12B. Sahelo–Sudanian subregion

    71 Sahel province
    72 Sudan province

##### 12C. Eritreo–Arabian subregion

    73 Somalia-Ethiopia province
    74 South Arabia province
    75 Socotra province

##### 12C. Omano-Sindian subregion

    76 Oman province
    77 South Iran province
    78 Sindia province

#### XIII. Karoo-Namib region

    79 Namibia province
    80 Namaland province
    81 Western Cape province
    82 Karoo province

#### XIV. St. Helena and Ascension region

    83 St. Helena and Ascension province

#### XV. Madagascan region

    84 Eastern Madagascar province
    85 Western Madagascar province
    86 Southern and Southwestern Madagascar province
    87 Comoro province
    88 Mascarenes province
    89 Seychelles province

#### XVI. Indian region

    90 Ceylon (Sri Lanka) province
    91 Malabar province
    92 Deccan province
    93 Upper Gangetic Plain province
    94 Bengal province

#### XVII. Indochinese region

    95 South Burma province
    96 Andamans province
    97 South China province
    98 Thailand province
    99 North Indochina province
    100 Annam province
    101 South Indochina province

#### XVIII. Malesian region
##### 18A. Malesian subregion

    102 Malaya province
    103 Borneo province
    104 Philippines province
    105 Sumatra province
    106 Java province

##### 18B. Papuan subregion

    107 Celebes province
    108 Moluccas and West New Guinea province
    109 Papua province
    110 Bismarck Archipelago province

#### XIX. Fijian region

    111 New Hebrides province
    112 Fiji province

#### XX. Polynesian region

    113 Micronesia province
    114 Polynesia province

#### XXI. Hawaiian region

    115 Hawaii province

#### XXII. Neocaledonian region

    116 New Caledonia province

### Neotropical kingdom
#### XXIII. Caribbean region

    117 Central America province
    118 West Indies province
    119 Galápagos Islands province

#### XXIV. Region of the Guayana Highlands

    120 The Guianas province

#### XXV. Amazon region

    121 Amazonia province
    122 Llanos province

#### XXVI. Brazilian region

    123 Caatinga province
    124 Central Brazilian Uplands province
    125 Chaco province
    126 Atlantic province
    127 Paraná province

#### XXVII. Andean region

    128 Northern Andes province
    129 Central Andes province

### South African kingdom
#### XXVIII. Cape region

    130 Cape province

### Australian kingdom
#### XXIX. Northeast Australian region

    131 North Australia province
    132 Queensland province
    133 Southeast Australia province
    134 Tasmania province

#### XXX. Southwest Australian region

    135 Southwest Australia province

#### XXXI. Central Australian or Eremaean region

    136 Eremaea province

### Antarctic kingdom
#### XXXII. Fernandezian region

    137 Juan Fernández province

#### XXXIII. Chile-Patagonian region

    138 Northern Chile province
    139 Central Chile province
    140 Pampas province
    141 Patagonia province
    142 Tierra del Fuego province

#### XXXIV. Region of the South Subantarctic Islands

    143 Tristan-Gough province
    144 Kerguelen province

#### XXXV. Neozeylandic region

    145 Lord Howe province
    146 Norfolk province
    147 Kermadec province
    148 Northern New Zealand province
    149 Central New Zealand province
    150 Southern New Zealand province
    151 Chatham province
    152 New Zealand Subantarctic Islands province

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

    (with focus on Europe, matching the image on the right)
* The central European region and the central Russian region are sister regions.
* The border between them is similar to the Fagus sylvatica limit (January, day-time temperature average: above -2 °C).
* The border between the central Russian region and the boreal region is similar to the Quercus spp. limit (Day-time temperature average: above 10 °C, 4 months per year).
* The border between the boreal region and the arctic region is similar to the tree line, taiga/arctic tundra limit (July, day-time temperature average: above 10 °C).
* The border of the Atlantic region is the limit of no frost (average), 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 (Olea europea is grown very North in Italy).
* The border between the submediterranean region and the central European region is similar to the alpine arc (upper Rhone, upper Rhine, lower Danube), a weather barrier.
* The Pontic region border is similar to the tree line/ steppe limit (less than 450 mm precipitation per year).
* 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
    1 African
    2 Indo-Malesian
    3 Australian
    4 Novozealandic
    5 Neotropical
    6 Chile–Patagonian
* Laurasian super-realm
    7 Holarctic
    8 Saharo-Arabian
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.