Botanical Studies (2009) 50: 467-475.
ECOLOGY
Biogeographical affinities of the flora of southeastern Yunnan, China1
Hua ZHU* and Li-Chun YAN
Kunming Section of Xishuangbanna Tropical Botanical Garden, Chinese Acackmy of Sciences, Xue-Fu Road 88, Kunming, Yunnan 650223, P. R. China
(Received May 1, 2007; Accepted May 14, 2009)
ABSTRACT. Southeastern Yunnan has 4,996 species and varieties of 1,357 genera and 186 families of native seed plants recorded. Floristic attributes and biogeographical affinities of the flora were studied by analyzing its floristic composition and geographical elements. Tropical genera comprise a majority (68.83%) of the flora and those of tropical Asian distribution contribute to 27.34% of the total genera. The flora of southeastern Yunnan is similar in composition to the floras of southern Yunnan, southwestern Guangxi and Vietnam. They have similarities of more than 89% at the family level and more than 76% at the generic level. The flora of southeastern Yunnan, with the compared floras together, belongs to the same floristic unit and is suggested to be part of Indo-Malaysian flora at northern margin of tropical Asia. However, the taxa of strictly tropical distribution are still underrepresented in the flora of southeastern Yunnan compared to Indo-Malaysian flora, and the families of mainly subtropical to temperate distribution, such as Magnoliaceae, Theaceae, Cornaceae, Styracaceae, Symplocaceae, Aquifoliaceae and Caprifoliaceae, are well represented in the flora. Some characteristic families of temperate East Asia, such as Diapensiaceae, Dipentodontaceae, Eupteleaceae, Grossulariaceae and Toricelliaceae are also present in the flora of southeastern Yunnan. These suggest that the flora of southeastern Yunnan is related to Eastern Asian flora more than other compared floras. It is also revealed that the flora of southeastern Yunnan is biogeographically closer to the flora of southwestern Guangxi than that of southern Yunnan.
Keywords: Biogeographical affinities; Flora; Southeastern Yunnan.
INTRODUCTION
Southern China is located at the northern edge of tropical Asia, and is composed of the southeasternmost part of Xizang (Tibet) (lower valleys of southern Himalayas), southwestern, southern and southeastern parts of Yunnan, southern Guangxi, southern Guangdong, southern Taiwan and Hainan Island. Southeastern Yunnan borders Vietnam, is situated in the southern extension of the Eastern Himalayas, and located at the demarcation line with tropical "SE Asia" to the south, temperate "Sino-Himalaya" to the north biogeographically.
Southeastern Yunnan is of extreme interest to botanists not only for its richness of primitive angiosperm taxa, such as species of Magnoliaceae and being a centre of palaeoendemism in China (Li, 1994), but also for its biodiversity richness, a hotspot for biodiversity of the world (Myers, 1998). The montane flora of southeastern
Yunnan is more of the nature of the temperate Sino-Himalaya flora, but the lowland flora is of the nature of the tropical Asian flora with representatives of Dipterocarpaceae.
The flora of south China and its tropical Asian floristic affinity have been discussed since the China-Russia expedition which penetrated deep into the areas of southwestern China in the late 1950s (Fedorov, 1957, 1958; Wu, 1965; Zhu, 1993, 1994a, 1994b, 1997, 2008a, 2008b; Zhu et al., 2001, 2003, 2004a, 2004b, 2006). However, most of the research on flora and vegetation in tropical southwestern China has been conducted in southern Yunnan. The flora of southeastern Yunnan and its biogeographical affinities are less known except some local works in nature reserves (Li et al., 2002; Zhang et
al., 2003; Shui et al., 2003; Wang et al., 2006; Zhu et al., 2007a).
To better understand the flora and its biogeographical affinities, the floristic composition and geographical elements of southeastern Yunnan were analyzed at family and generic levels. The floristic relationships of southeastern Yunnan to its neighboring southern Yunnan, southwestern Guangxi and Vietnam, are discussed by
1This project was funded by The National Natural Science Foundation of China (30770158, 30570128).
*Corresponding authors: E-mail: zhuh@xtbg.ac.cn; Fax:
86-871-5160916.
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Botanical Studies, Vol. 50, 2009
comparing the revised floristic inventories and checklists of these regions in this study.
Study site and topography
The area in southeastern Yunnan referred to in this study is located between the Tropic of Cancer and the Yunnan-Vietnam border, 22°26' ~ 23。26' N and 104°27'~ 108°48' E (Figure 1). It borders Vietnam to the south, and has a mountainous topography with the mountain ridges running in a north-south direction, decreasing in elevation southeastward. The region, including the six counties of Pingbian, Hekou, Jingping, Luchun, Yuanyang and Honghe, is c. 14,389 km2 in area and most of the area is limestone. Its altitude ranges from 74.6 m at the bottom of the lowest valley in the south (Hekou) to 3047.3 m at the top of Xilong Mountains in Jingping County.
Climate
The region has a monsoon climate. From the climatic station in Hekou County at 136.7 m alt. in the south of the region, the annual mean temperature is about 22.6°C and the annual cumulative temperature (the sum of daily temperature means > 10°C) is 8322.8°C. Annual precipitation is 1777.7 mm, of which more than 80% of the rainfall is in the rainy season from May to October. The average relative humidity is about 86% (Yunnan Meteorological Bureau, 1983). However, the region has a strong climatic variation with altitude. For example, in Pingbian county at 1414.1 m alt., the annual mean temperature is 16.5°, and the annual cumulative temperature (> 10°C) is 5933.2°C, as well as the annual precipitation is 1 621 . 4 mm, while in Fenshuiling of Jingping county at 2300 m alt., the annual mean temperature is 10.6°, and the annual cumulative temperature (> 10°C) is 2811.6°C, as well as the annual precipitation is 3287.4 mm (Xu, 2002).
Soil
T here are four main soil types in the region. Laterite soils occur in the area below 600 m altitude. Kanhaplohumoult soils occur in the areas between 600­1,200 m altitudes with a deep solum, but thin humus horizon. Paleudult soils derived from sandstone substrate occur in the areas between 1 ,200-1,900 m altitudes. Hapludalf soils occur in the areas above 1,900 m elevation. There is a large area of limestone in the region. The limestone hills have soil derived from a hard limestone substrate.
Vegetation
There are three main altitudinal zones of vegetation in the region. Below 800-900 m elevation is a seasonal rain forest in wet valleys and on lower slopes, and a monsoon forest in dry valleys. Between 900-2,000 m elevation is a lower montane rain forest in wet montane valleys, and an evergreen broad-leaved forest on slopes. An upper montane rain forest occurs on upper slopes
Figure 1. The study area in tropical southeastern Yunnan.
between 2,000-2,500 m elevations. Above 2,500 m elevation is a mossy dwarf forest and shrubs.
The seasonal rain forest, which is similar in forest profile, physiognomic characteristics and floristic composition to Southeast Asian rain forests, is a type of tropical Asian rain forest. It is characterized by tree species Pometia tomentosa, Parashorea chinensis, Dipterocarpus retusus, Hopea mollissima, Lysidice rhodostegia, Saraca dives and Garcinia paucinervis. The monsoon forest is a deciduous forest characterized by the deciduous tree species Bombax malabaricum, Albizia chinensis, Erythrina stricta, Lannea coromandelica, Sterculia pexa, Mayodendron igneum and Stereospermum tetragonum. The lower montane rain forest is characterized by tree species Madchuca pasquierii, Altingia yunnanensis, Podocarpus imbricatus, Beilshchmiedia fasciata, Michelia foveolata and Lithocarpus truncatus. The evergreen broad-leaved forest has a wide distribution and is the main montane vegetation type in the region. It is dominated by species of Fagaceae, Euphorbiaceae, Lauraceae and Theaceae, such as Castanopsis calcathiformis, Castanopsis hystrix, Castanopsis fleuryi, Lindera communis, Machilus tenuipilis, Machilus longipedicellata and Schima wallichii. The upper montane rain forest is characterized by the species Castanopsis wattii, Lithocarpus xylocarpus, Machilus viridis, Schima sinensis, Hartia sinensis, Diplopanax stachyanthus, Rehderodendron macrocarpum, Rhodoleia henryi and Alcimandra cathcartii. The mossy dwarf forest is characterized by Lithocarpus pachyphylloides, Vaccinium mandarinorum, Rhododendron irroratum, Myrsine stolonifera and Pieris formosa.
MATERIALS AND METHODS
Shui (2003) published a checklist of seed plants from subtropical to tropical southeastern Yunnan. From Shui' s work and references, we compiled a list of 4,996
ZHU and YAN ― Biogeography of southeastern Yunnan
469
species and varieties of native seed plants in 1,357 genera and 186 families from tropical southeastern Yunnan. C ircumscription of families and species follows w3 TROPICOS of Missouri Botanical Garden (http://mobot. mobot.org/W3T/Search/vast.html). Based on the plant list, the floristic and geographical attributes of the flora of southeastern Yunnan were analyzed. Patterns of seed plant distribution were quantified at the generic level based on Wu (1991). Adjacent southern Yunnan, southwestern Guangxi and Northern Vietnam are floristically similar to southeastern Yunnan. To discuss the floristic similarity and variation as well as biogeographical affinities among these regions, comparisons of floristic composition and geographical elements between southeastern Yunnan and neighbouring regions were made by using updated check­lists of their floras. The checklist of the flora of southern Yunnan refers to the Xishuangbanna administrative region (Zhu, 2008). Southwestern Guangxi refers also to its tropi­cal area that was recognised by referring distribution of tropical genera of seed plants (Zhu et al., 2007b) and the floristic regionalization of Fang et al. (1995), which ex­tends to northern Vietnam and lies between 21°30'〜23°10: N and 106°~109° E. The checklist of southwestern Guangxi was abstracted from the database of the Institute of Botany, CAS. The checklist of the Vietnamese flora (Le, 1999) was used for making comparisons, although Vietnam is floristically heterogeneous in its northern and southern parts.
RESULTS
Floristic composition
Four thousand nine hundred ninety six species and varieties in 1,357 genera and 186 families of native seed plants were recognized to occur in southeastern Yunnan. T he families with highest species richness include Fabaceae (70 genera/285 species), Orchidaceae (83/276), Rubiaceae (60/235), Poaceae (92/21 9), Asteraceae (59/180), Lauraceae (15/141), Urticaceae (17/134), Euphorbiaceae (41/126), Rosaceae (26/124), Fagaceae
(5/109) and Moraceae (7/104), Ericaceae (1 0/96),
Lamiaceae (39/91), Cyperaceae (13/87), Acanthaceae
(40/85) and Theaceae (9/81) (Table 1). Both the families of
mainly tropical elements, such as Orchidaceae, Rubiaceae, Lauraceae, Euphorbiaceae, Moraceae and Acanthaceae, and the families of mainly temperate elements, such as Fabaceae, Poaceae, Asteraceae, Lamiaceae, Rosaceae and Ericaceae have high species richness. The families Fagaceae and Theaceae, which are the dominant families in the forest of East Asia, also have high species richness in the flora.
Geographical elements at generic level
Patterns of seed plant distribution of the flora at the generic level are detailed in Table 2. The genera of tropi­cal Asian distribution, such as Alphonsea, Amoora, Pter-ospermum, Mitrephora, Mycetia, Aganosma, Chukrasia,
Table 1. The families of species richness in the flora of southeastern Yunnan.
Family
Genus
Species % of the total species
Fabaceae
70
285
5.70
Orchidaceae
83
276
5.52
Rubiaceae
60
235
4.70
Poaceae
92
219
4.38
Asteraceae
59
180
3.60
Lauraceae
15
141
2.82
Urticaceae
17
134
2.68
Euphorbiaceae
41
126
2.52
Rosaceae
26
124
2.48
Fagaceae
5
109
2.18
Moraceae
7
104
2.08
Ericaceae
10
96
1.92
Lamiaceae
39
91
1.82
Cyperaceae
13
87
1.74
Acanthaceae
40
85
1.70
Theaceae
9
81
1.62
Gesneriaceae
21
79
1.58
Liliaceae
22
64
1.32
Celastraceae
10
65
1.30
Araliaceae
16
64
1.28
Vitaceae
9
60
1.20
Verbenaceae
10
60
1.20
Myrsinaceae
4
60
1.20
Scrophulariaceae
26
59
1.18
Rutaceae
15
58
1.16
Melastomataceae
16
58
1.16
Annonaceae
12
54
1.08
Asclepiadaceae
23
53
1.06
Polygonaceae
5
52
1.04
Magnoliaceae
14
52
1.04
Araceae
18
52
1.04
Begoniaceae
1
51
1.02
Zingiberaceae
11
50
1.00
Apocynaceae
23
47
0.94
Smilacaceae
2
43
0.86
Sterculiaceae
11
41
0.82
Cucurbitaceae
13
41
0.82
Ranunculaceae
7
38
0.76
Caprifoliaceae
8
37
0.74
Aquifoliaceae
1
35
0.70
Piperaceae
3
34
0.68
Convolvulaceae
12
34
0.68
Commelinaceae
12
32
0.64
Oleaceae
6
30
0.60
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Botanical Studies, Vol. 50, 2009
Crypteronia, and Knema, show the highest percentage among all distribution types, contributing 27.34% to the flora. Genera of Pantropical distribution, such as Gnetum, Cryptocarya, Capparis, Piper, Croton, Dioscorea, Uncaria, Morinda, Ardisia, Bauhinia, Marsdenia etc., contribute 17.96% to the flora. Next are the genera of Old World tropical distribution, such as Thunbergia,
Dracaena, Pandanus, Ventilago, Stephania, Fissistigma, Polyalthia, Barringtonia, Carallia, Canarium, Chasalia and Uvaria, contributing 8.55%. Genera with distributions from tropical Asia to tropical Australia include Hoya, Argyreia, Dillenia, Lagerstroemia, Loesenneriella, Murray and Toona. Genera of tropical Asian to tropical Africa distribution include Bombax, Flacourtia, Bridenia, Premna, Strophanthus, Mitragyna, Garcinia, Anogeissus, and Cymbo pogon. Genera of tropical distribution in all (types 2〜7) comprise 68.83% of the total number. The genera of Northern temperate distribution such as Artemisia, Carpinus, Betula, Salix, Cornus, Corydalis, Pinus, and Sorbus contribute to 8.18% of the total genera. The genera of East Asian distributions such as Actinidia, Belamcandia, Aspidistra, Cephalotaxus, Choerospondia, Gardneria, Hovenia, Pegia, Skimmia, Stachyrus, Pterocarya, contribute to 8.84% of the total genera. Other genera include those which have a disjunct distribution in East Asia and North America, such as Schizandra, Photinia, Nyssa, Osmanthus, Magnolia, Mahonia, Illicium, Castanopsis etc., and Old World temperate distributions such as Ajuga, Elsholzia, Herminium, Inula, Ligustrum, Paris etc. There are 41 genera which are endemic or approximately endemic to China, including Bretschneidera, Camptotheca, Cephalantheropsis, Craspedolobium, Delavaya, Dipteronia, Eleutharrhena, Emmenopterys, Glyptostrobus, Gymnotheca, Hemiboeopsis, Neohusnotia, Tapiscia, Tetrapanax etc.
Comparison of the floras of southern Yunnan, southwestern Guangxi of SW China and Vietnam
The floristic similarities at the family and generic lev­els between southeastern Yunnan and southern Yunnan (Xishuangbanna), southwestern Guangxi and Vietnam are given in Table 3. The similarities in the flora of south­eastern Yunnan and those compared floras exceed 89% at the family level and more than 76% at the generic level. The flora of southeastern Yunnan shows a higher floristic similarity to the flora of southwestern Guangxi than to the flora of southern Yunnan at the family and generic levels.
Table 2. Geographical elements of seed plants at the generic level in the flora of southeastern Yunnan.
Geographical elements at generic level
Number of genera
1 Cosmopolitan
62
4.57
2 Pantropic
240
17.69
3 Tropical Asia and Tropical America
30
2.21
disjunct
4 Old World Tropic
116
8.55
5 Tropical Asia to Tropical Australia
82
6.04
6 Tropical Asia to Tropical Africa
95
7.00
7 Tropical Asia
371
27.34
8 North Temperate
111
8.18
9 East Asia and North America disjunct
47
3.46
10 Old World Temperate
32
2.36
11 Temperate Asia
6
0.44
12 Mediterranean, W Asia to C Asia
3
0.22
13 Center Asia
1
0.07
14 East Asia
120
8.84
15 Endemic to China
41
3.02
Total no. of genera
1357
100
*The no. of genera in each geographical element divided by the no. of genera of all geographical elements, then multiplied by 100%. '
Table 3. Similarity coefficients at family and genus levels between the floras of southern Yunnan, southeastern Yunnan, southwestern Guangxi and Vietnam.
Similarity coefficients
Southern Yunnan/ Southeastern Yunnan
Southwestern Guangxi/ Southeastern Yunnan
Vietnam/Southeastern Yunnan
At family level
163/89.6*
177/95.2
176/94.6
At genus level
939/79.9**
857/84.68
1036/76.34
*Shared no. of families/ Similarity coefficients; "Shared no. of genera/ Similarity coefficients.
Similarity coefficient between A and B = The number of taxa shared by both A and B divided by the number of taxa of A or B which has less taxa, then multiplied by 100%.
Data for tropical southwestern Guangxi is from the database of Institute of Botany, CAS, from which we compiled a plant list with 190 families and 1012 genera of seed plants. Data for southern Yunnan is from Zhu (2008), in which a plant list with 182 families and 1176 genera of seed plants were enumerated. Data for Vietnam is from Le (1999), from which a plant list with 214 families and 1817 genera of seed plants were compiled.
ZHU and YAN ― Biogeography of southeastern Yunnan
471
Table 4. The twenty families with most species richness among the tropical floras of southern, southeastern Yunnan, southwestern Guangxi and Vietnam.
Flora of southern Yunnan Flora of southeastern Yunnan Flora of southwestern Guangxi
Flora of Vietnam
Family
Species %*
Family
Species %
Family
Species %
Family
Species %
Orchidaceae
9.82
Fabaceae
5.70
Fabaceae
6.06
Fabaceae
6.98
Fabaceae
6.32
Orchidaceae
5.52
Euphorbiaceae
3.90
Orchidaceae
6.90
Rubiaceae
4.25
Rubiaceae
4.70
Rubiaceae
3.90
Poaceae
5.73
Poaceae
3.95
Poaceae
4.38
Asteraceae
3.46
Rubiaceae
4.72
Euphorbiaceae
3.50
Asteraceae
3.60
Orchidaceae
3.09
Euphorbiaceae
4.50
Asteraceae
3.17
Lauraceae
2.82
Poaceae
2.94
Cyperaceae
3.61
Moraceae
2.19
Urticaceae
2.68
Lauraceae
2.53
Asteraceae
3.26
Lauraceae
2.10
Euphorbiaceae
2.52
Rosaceae
2.42
Lauraceae
2.71
Urticaceae
2.16
Rosaceae
2.48
Urticaceae
2.16
Fagaceae
2.37
Zingiberaceae
2.10
Fagaceae
2.18
Fagaceae
2.12
Acanthaceae
2.17
Acanthaceae
2.04
Moraceae
2.08
Moraceae
1.75
Annonaceae
1.87
Lamiaceae
1.83
Ericaceae
1.92
Rutaceae
1.71
Apocynaceae
1.72
Asclepiadaceae
1.74
Lamiaceae
1.82
Zingiberaceae
1.71
Myrsinaceae
1.56
Apocynaceae
1.53
Cyperaceae
1.74
Asclepiadaceae
1.67
Moraceae
1.53
Annonaceae
1.47
Acanthaceae
1.70
Gesneriaceae
1.67
Verbenaceae
1.46
Verbenaceae
1.44
Theaceae
1.62
Apocynaceae
1.60
Lamiaceae
1.42
Cucurbitaceae
1.38
Gesneriaceae
1.58
Liliaceae
1.60
Araceae
1.42
Rosaceae
1.38
Liliaceae
1.32
Myrsinaceae
1.56
Rosaceae
1.38
Vitaceae
1.35
Celastraceae
1.30
Lamiaceae
1.45
Zingiberaceae
1.38
Fagaceae
1.32
Araliaceae
1.28
Vitaceae
1.38
Melastomataceae
1.31
*Species % indicates their percentage within the respective floras (the number of species for each family divided by the total number of species in the respective floras x100). The families showed in bold are the top twenty families, which are only in the flora of the tropical southeastern Yunnan.
The comparisons of the twenty families with the most species among these floras are enumerated in Table 4.
The top ranking families in all compared floras are basically the same. The families Zingiberaceae and Apocynaceae represent in the floras of southern Yun­nan, southwestern Guangxi and Vietnam among the top twenty families, but not in the top twenty in the flora of southeastern Yunnan. Annonaceae and Verbenaceae are in the top twenty ranking families of the floras of southern Yunnan and Vietnam, while Liliaceae and Gesneriaceae are in the top twenty ranking families of the floras of southeastern Yunnan and southwestern Guangxi. How­ever, Ericaceae, Theaceae, Celastraceae and Araliaceae are only in the top twenty ranking families of the flora of southeastern Yunnan. On the other hand, some families with less species richness, such as the mainly temperate families Coriariaceae, Diapensiaceae, Dipentodontaceae, Eupteleaceae, Grossulariaceae and Toricelliaceae present in southeastern Yunnan, but not in the floras of southern Yunnan and Vietnam.
If we rank the families of high species richness (more than 20 species) by their species percentage in the total of the family (The number of species for each family in the respective floras divided by the total number of species of the family worldwide), we obtained a different ranking pattern (Table 5). Magnoliaceae ranks first in the floras of southeastern Yunnan, southwestern Guangxi and Viet­nam among the top ten families, followed by Theaceae. Smilacaceae and Caprifoliaceae are shared by the floras of southeastern Yunnan, southwestern Guangxi in the top ten families, while Symplocaceae is shared by south­eastern Yunnan and Vietnam. However, Cornaceae and Styracaceae are among the top ten families only in south­eastern Yunnan.
C omparisons of geographical elements at generic level from these regional floras revealed that the tropical elements (type 2~7) contribute more than 68% of the total genera in all these compared floras, and that the highest proportion of the tropical elements occurs in the flora of southern Yunnan (comprising 78.3% of all the genera)
472 Botanical Studies, Vol. 50, 2009
Table 5. Comparison of the families ranked by their species percentage of the total in the family in the regional floras.
Southern Yunnan
Species % of the family*
Southeastern Yunnan
Species % of the family*
Southwestern Guangxi
Species % of the family*
Vietnam
Species % of the family*
Urticaceae
6.86
Magnoliaceae
31.52
Magnoliaceae
14.55
Magnoliaceae
31.52
Menispermaceae
6.67
Cornaceae
23.33
Fagaceae
8.14
Fagaceae
30.43
Moraceae
6.64
Fagaceae
15.57
Smilacaceae
6.25
Theaceae
16.07
Meliaceae
6.55
Smilacaceae
13.44
Caprifoliaceae
6.19
Meliaceae
13.63
Zingiberaceae
6.36
Theaceae
13.28
Theaceae
5.90
Symplocaceae
12.80
Fagaceae
6.29
Urticaceae
12.76
Urticaceae
5.52
Ebenaceae
12.78
Cucurbitaceae
5.94
Styracaceae
12.50
Menispermaceae
4.89
Verbenaceae
13.79
Vitaceae
5.29
Symplocaceae
10.40
Vitaceae
4.35
Moraceae
12.55
Commelinaceae
4.84
Moraceae
9.45
Moraceae
4.27
Myrsinaceae
11.43
Verbenaceae
4.17
Caprifoliaceae
8.81
Zingiberaceae
4.18
Zingiberaceae
11.27
* The number of species for each family in the respective floras divided by the total number of species of the family worldwide. The families showed in bold are the characteristic families of temperate East Asian flora.
Table 6. Comparison of geographical elements at generic level between the floras of southern, southeastern Yunnan, southwestern
Guangxi and Vietnam (%)*.
Geographical elements of genera
Flora of southern Yunnan
Flora of southeastern Yunnan
Flora of southwestern Guangxi
Flora of Vietnam
1 Cosmopolitan
5
4.57
5.43
4.35
2 Pantropic
21.3
17.69
20.06
18.00
3 Tropical Asia and Tropical America disjunct
2.6
2.21
2.96
2.92
4 Old World Tropic (Tropical Africa via Tropical
9.5
8.55
9.19
9.08
Asia to Tropical Australia)
5 Tropical Asia to Tropical Australia
6.5
6.04
9.98
7.82
6 Tropical Asia to Tropical Africa
8.2
7.00
4.45
8.26
7 Tropical Asia or Indo-Malesia
30.2
27.34
23.22
29.33
8 North Temperate
5.1
8.18
7.71
6.49
9 East Asia and North America disjunct
2.7
3.46
3.95
3.08
10 Old World Temperate
2
2.36
2.96
2.48
11 Temperate Asia
0.4
0.44
0.49
0.50
12 Mediterranean, W. Asia to C. Asia
0.2
0.22
0.30
0.83
13 Center Asia
0.1
0.07
0.00
0.06
14 East Asia
5.3
8.84
7.11
5.12
15 Endemic to China
0.9
3.02
2.17
0.00
16 Endemic to Vietnam
1.71
Data for Southern Yunnan used here is from Zhu (2008) (1176 genera included); Data for tropical southwestern Guangxi used here is from database of the Institute of Botany, CAS (1012 genera included); Data for Vietnam is from Li (1999) (1817 genera included).
ZHU and YAN ― Biogeography of southeastern Yunnan
473
(Table 6). All the compared floras have very similar geographical elements except the flora of southeastern Yunnan which has a slightly higher proportion of the geographical elements of East Asia, North Temperate and endemic to China.
Conclusions and discussion
Tropical genera comprise a majority (68.83%) of the flora of southeastern Yunnan. The dominant genera are those restricted to tropical Asia (27.34% of the total genera). This reveals that the flora of southeastern Yun­nan is tropical in nature and has tropical Asian affinity although it occurs at the southern extension of the Eastern Himalayas.
The flora of southeastern Yunnan is similar to the floras of southern Yunnan, southwestern Guangxi and Vietnam in the families with the greatest species richness, and has high similarities to them at family and generic levels (more than 89% at the family level and more than 76% at the generic level). It is further confirmed that southeastern Yunnan, southern Yunnan, southwestern Guangxi and Vietnam are floristically continuous. The flora of southeastern Yunnan, along with these other floras, belongs to the same floristic unit and is part of tropical Asian or Indo-Malaysian flora in floristic regionalization. However, the families Ericaceae, Theaceae, Celastraceae and Araliaceae, which are well developed in East Asia, are in the top twenty ranking families of the flora of southeastern Yunnan only, while the more strictly tropical families, such as Zingiberaceae, Verbenaceae, Apocynaceae and Annonaceae are in the top twenty ranking families of the other compared floras. Some temperate East Asian families, such as Coriariaceae, Diapensiaceae, Dipentodontaceae, Eupteleaceae, Grossulariaceae and Toricelliaceae are exclusively present in southeastern Yunnan. These suggest that the flora of southeastern Yunnan is related to temperate Eastern Asian flora more than the other compared floras. The flora of southeastern Yunnan has also a lower percentage of tropical elements and more temperate elements than those of southern Yunnan, southwestern Guangxi and Vietnam. These features of the flora of southeastern Yunnan corre­spond well to the large cover of montane vegetation in the area.
Although tropical families and genera in a broad sense contribute most to its total flora, the taxa of strictly tropical distribution are still underrepresented in southeastern Yunnan, compared to the Malaysian flora. For example, Dipterocarpaceae has only four species of three genera respectively in southeastern Yunnan although they are the most abundant trees in some forest types. The flora of southeastern Yunnan is a marginal part of the tropical Asian flora.
In the families ranked by species percentage in the total of the family worldwide (Table 5), Magnoliaceae ranks the first in the flora of southeastern Yunnan, followed by Cornaceae, Smilacaceae, Theaceae, Styracaceae, Symplocaceae and Caprifoliaceae in the top ten ranking
families. These families are not only the characteristic families of the temperate East Asian flora, but also the ones well represented in the flora of southeastern Yunnan. The families with most species richness are not the same as the ones that well represented in the flora of southeastern Yunnan. These floristic patterns are quite different from those in Malesian floras, for example, in the flora of Malay Peninsula (Turner, 1995), the families Dipterocarpaceae, Zingiberaceae, Clusiaceae, Annonaceae, Rubiaceae, Apocynaceae, Arecaceae, Euphorbiaceae, Myrtaceae and Melastomataceae are the families with most species richness, but also the families that well represented in Malesia (Zhu and Roos, 2004). It is implied that the flora of southeastern Yunnan had a historical connection to Eastern Asian flora in origin, but deeply permeated by Malesian floristic elements. The flora of southeastern Yunnan has also a closer affinity to the floras of southwestern Guangxi and Vietnam than to the flora of southern Yunnan by sharing more of the well represented families in these regions. Studies on the geological history of SE Asia revealed that southeastern Yunnan and south­western Guangxi were derived from South China Block or Yangzi Block, while southern Yunnan was part of Shan-Thai Block or Simao Block with Ailaoshan-Song Ma or Ailaoshan Belt being a suture zone (Feng et al.,
2005; Metcalfe, 2006; Lepvriere et al., 2008). Our results
could be well explained by the geological history of these regions. It is also revealed that direct land connection between mainland SE Asia and western Malesia existed until the early Pliocene (5 million years ago) (Hall, 1998), and there was no geographical barrier between Yunnan, mainland SE Asia and west Malesia during most of the Tertiary (Morley, 1998). The geological history may explain the high percentage of tropical floristic elements, including tropical Asian elements, in the flora of southeast­ern Yunnan.
Acknowledgments. This project was funded by The National Natural Science Foundation of China (30770158, 3 05 7 01 28). F igure 1 was made by Dr. Hu Huabin. We thank anonymous reviewers for their constructive comments on this article. We also thank Dr. Douglas A. Schaefer for his help in English improvements in this article.
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ZHU and YAN ― Biogeography of southeastern Yunnan
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雲南東南部熱帶植物區系的生物地理親緣
朱 華 閏麗春
中國科學院西雙版納熱帶植物園
雲南東南部熱帶地區記錄有種子植物186科，1,357 屬，4,996 種及變種。通過分析其植物區系
組成和地理成分，本文研究了該植物區系的特徵及其生物地理親緣。該植物區系熱帶成分占總屬數的
68.83% ，其中，又以熱帶亞洲分佈屬比例最高，占總屬數的27.34% 。在與周邊雲南南部（西雙版納）、
廣西西南部及越南植物區系的比較上，雲南東南部的熱帶植物區系與它們在科、屬水準上具有高的類似
性，它們之間科的類似性在89% ，屬的類似性在76%以上。它們隸屬于同一植物區系分區單元，在植
物區系分區中為熱帶亞洲或印度一馬來西亞植物區系的北緣部分。由於位於東南亞熱帶北緣山地及其
地質歷史原因，雲南東南部的熱帶植物區系中嚴格熱帶分佈的成分不多，仍以邊緣熱帶成分為主，並有
相對豐富的亞熱帶-溫帶科如木蘭科、山茶科、山茱萸科、山礬科、忍冬科、冬青科等以及一些東亞和
喜馬拉雅特徵科，如岩梅科、十齒花科、領春木科、茶薦子科和鞘柄木科，顯示了它與東亞溫帶植物區
系也有較多聯繫。與雲南南部、廣西西南部及越南熱帶植物區系比較，雲南東南部植物區系中熱帶地理
成分的比例相對較低，並且與廣西西南部的聯繫強于雲南南部。
關鍵詞：生物地理親緣：植物區系；雲南東南部。