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 some schemes, areas of phytochoria are classified hierarchically, e.g., in Floral (or Floristic, Phytogeographic) Kingdoms, Regions and Provinces, sometimes including the categories Empire and Domain, while others prefer not to rank areas, referring to them simply as "regions" or "phytochoria".

The 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 (e.g., phytophysiognomies, formations, biomes) may variably take in account, according to 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 taxons. 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.

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.

Good's floristic regionalization

Floristic kingdoms

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

Takhtajan's floristic regionalization

Armen Takhtajan, 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

Flora regions in Europe

I. Circumboreal Region

1 Arctic

2 Atlantic Europe

3 Central Europe

4 Illyria or Balkan

5 Pontus Euxinus

6 Caucasus

7 Eastern Europe

8 Northern Europe

9 Western Siberia

10 Altai-Sayan

11 Central Siberia

12 Transbaikalia

13 Northeastern Siberia

14 Okhotsk-Kamchatka

15 Canada incl. Great Lakes

II. Eastern Asiatic Region

16 Manchuria

17 Sakhalin-Hokkaidō

18 Japan-Korea

19 Volcano-Bonin

20 Ryūkyū or Tokara-Okinawa

21 Taiwan

22 Northern China

23 Central China

24 Southeastern China

25 Sikang-Yuennan

26 Northern Burma

27 Eastern Himalaya

28 Khasi-Manipur

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

31 North American Prairies

IV. Rocky Mountain Region

32 Vancouver

33 Rocky Mountains

V. Macaronesian Region

34 Azores

35 Madeira

36 Canaries

37 Cape Verde

VI. Mediterranean Region

38 Southern Morocco

39 Southwestern Mediterranean

40 South Mediterranean

41 Iberia

42 Baleares

43 Liguria-Tyrrhenia

44 Adriatic

45 East Mediterranean

46 Crimea-Novorossijsk

VII. Saharo-Arabian Region

47 Sahara

48 Egypt-Arabia

VIII. Irano-Turanian Region

49 Mesopotamia

50 Central Anatolia

51 Armenia-Iran

52 Hyrcania

53 Turania or Aralo-Caspia

54 Turkestan

55 Northern Baluchistan

56 Western Himalaya

57 Central Tien Shan

58 Dzungaria-Tien Shan

59 Mongolia

60 Tibet

IX. Madrean Region

61 Great Basin

62 Californian

63 Sonoran

64 Mexican Highlands

Paleotropical Kingdom

X. Guineo-Congolian Region

65 Upper Guinean forests

66 Nigeria-Cameroon

67 Congo

XI. Usambara-Zululand Region

68 Zanzibar-Inhambane

69 Tongoland-Pondoland

XII. Sudano-Zambezian Region

70 Zambezi

71 Sahel

72 Sudan

73 Somalia-Ethiopia

74 South Arabia

75 Socotra

76 Oman

77 South Iran

78 Sindia

XIII. Karoo-Namib Region

79 Namibia

80 Namaland

81 Western Cape

82 Karoo

XIV. St.Helena and Ascension Region

83 St. Helena and Ascension

XV. Madagascan Region

84 Eastern Madagascar

85 Western Madagascar

86 Southern and Southwestern Madagascar

87 Comoro

88 Mascarenes

89 Seychelles

XVI. Indian Region

90 Ceylon (Sri Lanka)

91 Malabar

92 Deccan

93 Upper Gangetic Plain

94 Bengal

XVII. Indochinese Region

95 South Burma

96 Andamans

97 South China

98 Thailand

99 North Indochina

100 Annam

101 South Indochina

XVIII. Malesian Region

102 Malaya

103 Borneo

104 Philippines

105 Sumatra

106 South Malesia

107 Celebes

108 Moluccas and West New Guinea

109 Papua

110 Bismarck Archipelago

XIX. Fijian Region

111 New Hebrides

112 Fiji

XX. Polynesian Region

113 Micronesia

114 Polynesia

XXI. Hawaiian Region

115 Hawaii

XXII. Neocaledonian Region

116 New Caledonia

Neotropical Kingdom

XXIII. Caribbean Region

117 Central America

118 West Indies

119 Galápagos Islands

XXIV. Region of the Guayana Highlands

120 The Guianas

XXV. Amazonian Region

121 Amazonia

122 Llanos

XXVI. Brazilian Region

123 Caatinga

124 Central Brazilian Uplands

125 Chaco

126 Atlantic Brazil

127 Parana

XXVII. Andean Region

128 Northern Andes

129 Central Andes

South African Kingdom

XXVIII. Cape Region

130 Cape Province

Australian Kingdom

XXIX. Northeast Australian Region

131 North Australia

132 Queensland

133 Southeast Australia

134 Tasmania

XXX. Southwest Australian Region

135 Southwest Australia

XXXI. Central Australian or Eremaean Region

136 Eremaea

Antarctic Kingdom

XXXII. Fernandezian Region

137 Juan Fernández

XXXIII. Chile-Patagonian Region

138 Northern Chile

139 Central Chile

140 Pampas

141 Patagonia

142 Tierra del Fuego

XXXIV. Region of the South Subantarctic Islands

143 Tristan-Gough

144 Kerguelen

XXXV. Neozeylandic Region

145 Lord Howe

146 Norfolk

147 Kermadec

148 Northern New Zealand

149 Central New Zealand

150 Southern New Zealand

151 Chatham

152 New Zealand Subantarctic Islands

References

• Cox, C. B. (2001). The biogeographic regions reconsidered. Journal of Biogeography, 28(4): 511-523.

• Good, Ronald (1947). The Geography of Flowering Plants. Longmans, Green and Co, New York

• Nelson, G.J. (1978). From Candolle to Croizat: Comments on the history of biogeography. Journal of the History of Biology, 11: 269–305.

• Takhtajan, Armen (1986). Floristic Regions of the World. (translated by T.J. Crovello & A. Cronquist). University of California Press, Berkeley.

• Udvardy, M. D. F. (1975). A classification of the biogeographical provinces of the world. IUCN Occasional Paper no. 18. Morges, Switzerland: IUCN. [1]ca:Regió florística