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, or ecotone. 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
12D. 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.
References
Bibliography Frodin, D.G. (2001). Guide to Standard Floras of the World. An annotated, geographically arranged systematic bibliography of the principal floras, enumerations, checklists and chorological atlases of different areas. 2nd ed. (1st edn 1984), pp. xxiv, 1100, .Cambridge University Press, Cambridge, [17].