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
Good (1947) floristic kingdoms
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.
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
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
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
XXVIII.
Cape region
130
Cape province
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
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)
Flora regions in Europe
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.
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. 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
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