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,[1] 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".[2]
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.[3] 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.[4]
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)[5] 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,[6] mainly in Africa.[7]
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.
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).[8] [9] His Syllabus der Pflanzenfamilien, from the third edition (1903) onwards, also included a sketch of the division of the earth into floral regions.[10]
Other important early works on floristics includes Augustin de Candolle (1820),[11] Schouw (1823),[12] Alphonse de Candolle (1855),[13] Drude (1890),[14] Diels (1908),[15] and Rikli (1913).[16]
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.[17]
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.[18] [19] [20] [21]
1 Arctic province
2 Atlantic Europe province
3 Central Europe 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
15 Canada incl. Great Lakes province
16 Manchuria 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
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
32 Vancouverian province
33 Rocky Mountains province
34 Azores province
35 Madeira province
36 Canaries province
37 Cape Verde province
38 Southern Morocco province
39 Southwestern Mediterranean province
40 South Mediterranean province
41 Iberia province
42 Baleares province
44 Adriatic province
45 East Mediterranean province
46 Crimea-Novorossijsk province
47 Sahara province
48 Egypt-Arabia province
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
57 Central Tien Shan province
58 Dzungaria-Tien Shan province
59 Mongolia province
60 Tibet province
61 Great Basin province
62 Californian province
63 Sonoran province
64 Mexican Highlands province
65 Upper Guinean forests province
66 Nigeria-Cameroon province
67 Congo province
68 Zanzibar-Inhambane province
69 Tongoland-Pondoland province
70 Zambezi province
71 Sahel province
72 Sudan province
74 South Arabia province
75 Socotra province
76 Oman province
78 Sindia province
79 Namibia province
80 Namaland province
81 Western Cape province
82 Karoo province
83 St. Helena and Ascension province
84 Eastern Madagascar province
85 Western Madagascar province
86 Southern and Southwestern Madagascar province
87 Comoro province
88 Mascarenes province
89 Seychelles province
90 Ceylon (Sri Lanka) province
91 Malabar province
92 Deccan province
93 Upper Gangetic Plain province
94 Bengal province
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
102 Malaya province
103 Borneo province
104 Philippines province
105 Sumatra province
106 Java province
107 Celebes province
108 Moluccas and West New Guinea province
109 Papua province
110 Bismarck Archipelago province
111 New Hebrides province
112 Fiji province
113 Micronesia province
114 Polynesia province
115 Hawaii province
116 New Caledonia province
117 Central America province
118 West Indies province
119 Galápagos Islands province
120 The Guianas province
121 Amazonia province
122 Llanos province
123 Caatinga province
124 Central Brazilian Uplands province
125 Chaco province
126 Atlantic province
127 Paraná province
128 Northern Andes province
129 Central Andes province
130 Cape province
131 North Australia province
132 Queensland province
133 Southeast Australia province
134 Tasmania province
135 Southwest Australia province
136 Eremaea province
137 Juan Fernández province
138 Northern Chile province
139 Central Chile province
140 Pampas province
141 Patagonia province
142 Tierra del Fuego province
144 Kerguelen province
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
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.[24]
1 African
2 Indo-Malesian
3 Australian
4 Novozealandic
5 Neotropical
6 Chile-Patagonian
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.[25] 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.[26]