The Origin, Dispersal and Formation of the Distribution Pattern of Swertia L. (Gentianaceae)

Abstract

Abstract:

The genus Swertia is one of the large genera in Gentianaceae, including 154

species, 16 series and 11 sections. It is disjunctly distributed in Europe, Asia, Africa and N.

America, but entirely absent from Oceania and S. America.

According to Takhtajan’s (1978) regionalization of the world flora, Swertia is found in

14 regions. Eastern Asiatic region with 86 species, of which 58 are local endemics, 13 series

and 9 sections, ranks the first among all the regions. The highest concentration of the taxa

and endemics in Eastern Asiatic region occurs in SW China-Himalayan area (Sikang-Yunnan

P. , W. Sichuan, W. Yunnan-Guichou Plateau of China and NE. Burma, N. Burmense P. ,

E. Himalayan P. and Khasi-Manipur P. ). In this area there are 74 species (48 endemics),

12 series, and 9 sections; thus about half species of the world total, three quarters of series

and 82% of sections occur in this small area. Besides, the taxa at different evolutionary

stages in Swertia also survive here. It is an indication that SW. China-Himalayan area is a

major distribution centre of the genus Swertia. In addition, Sudan-Zambezian Region in

Africa, with 22 species, 4 series and 2 sections, is a second distribution centre.

The primitive type of the genus Swertia is Sect. Rugosa which consists of 2 series and

23 species. It is highly centred in the mountains of SW. China (Yunnan, Sichuan, Guizhou

and SE. Xizang) where 2 series and 16 species occur. Among them 15 species of Ser. Ru-

gosae were considered as the most primitive groups in this genus. From our study, the out-

group of Swertia is the genus Latouchea Frahch. , which is distributed in Yunnan, Sichuan,

Guizhou, Hunan, Guangdong, Guangxi and Fujian. The two groups overlap in distribution

in SW. China. According to the principle of common origin, the ancestor of two genera ap-

peared most probably in this overlapping area. It was inferred that SW. China Was the birth-

place of the genus Swertia.

Four sections of Swertia have different disjunct distribution patterns: Sect. Ophelia is of

Tropic Asia, Africa and Madagascar disjunct distribution; sect. Swertia is of north temper-

ate distribution; sect. Spinosisemina is in Tropical Asia (Trop. India to S. China and Philip-

ines); sect. Platynema also is in Tropical Asia (Java, Sumatra, Himalayas to SW. China).

These disjunct patterns indicate that the Swertia floras between the continents or between

continent and islands have a connection with each other. From paleogeographical analysis,

Swertia plants dispersed to Madagascar before the Late Cretaceous, to SE. Asian Islands in

the Pleistocene, to North America in the Miocene. The distribution of Swertia in Madagas-

car might be later than that in Asia. Therefore the origin time of the genus Swertia was at

least not later than the Late Cretaceous, and might be back to the Mid-Cretaceous.

The genus Swertia first fully developed and differentiated, forming some taxa at differ-

ent evolutionary stages (Rugosa, Swertia, Poephila, Ophelia and Platynema etc. ) in the o-

riginal area, and these taxa quickly dispersed in certain directions during the Late Creta-

ceous-Middle Tertiary when the global climate was warm and no much change. There seem

to be three main dispersal routes from the origin area to different continents; (1) The west-

ward route i. e. from SW. China, along the Himalayas area to Kashmir, Pakistan,

Afghanistan and Iran, and then southwestwards into Africa throuth Arabia. Four sections

(Poephila, Macranthos, Kingdon-Wardia and Ophelia) took this dispersal route. Most

species of sect. Ophelia dispersed along this route, but a few along southern route and north

ern route. Sect. Ophelia greatly differentiated in Africa and the African endemic section-

Sect. Montana was derived from it. The two sections form there a second distribution center

of Swertia. (2) The southward route, i. e. towards S. India through the Himalayas, and

towards SE. Asian islands through C. and S. China, Indo-China. Along this dispersal route

sect. Platynema, Sect. Spinosisemina and a few species of Sect. Ophelia dispersed; (3) The

northward rout, i. e. northwards across N. China, C. Asia to a high latitude of Euasia,

and also through E. Asia into N. America. The following groups took this route: sect. Ru-

gosa, sect. Swertia, sect. Frasera, sect. Heteranthos and sect. Ophelia ser. Dichotomae.

Therefore, it seems that the genus Swertia originated in SW. China and then dispersed

from there to N. and S. Asia, Africa, Europe and North America and formed the modern

distribution pattern of this genus.

Key words: Swertia, Endemic plants, Distribution pattern, Origin area, Dispersal route

Ho Ting-nong, Xue Chun-ying, Wang Wei. The Origin, Dispersal and Formation of the Distribution Pattern of Swertia L. (Gentianaceae)[J]. .

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[4]	Zhang Ming-li. The Geographic Distribution of the Genus Caragana in Qinghai-Xizang Plateau and Himalayas [J]. , 1997, 35(2): 136-147.
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The Origin, Dispersal and Formation of the Distribution Pattern of Swertia L. (Gentianaceae)

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