Characteristics and affinity of the flora of Xishuangbanna, SW China

Abstract

The flora of Xishuangbanna,SW China,is recorded to consist of 3 336 native seed plant species belonging to 1 140 genera and 197 families,of which the family Ochidaceae with 334 species is the largest family in size;Papilionaceae with 182 species is the second;Rubiaceae with 147 species is the third;and other families are ranked as following:Gramineae(143 species),Euphorbiaceae(119),Compositae(107),Moraceae(77),Urticaceae(72),Lauraceae(68),Zingiberaceae(67),Asclepiadaceae(62),Apocynaceae(61),Labiatae(59),Annonaceae(52),Cucurbitaceae(50),Acanthaceae(49)Rosaceae(49),Fagaceae(45),Araceae(43)etc. The statistics of distribution patterns of taxa shows that the families and genera of tropical distribution make up 60 1% and 83 5% of the total sum of the flora separately. Furthermore,the genera of tropical Asian distribution contribute 32 8% of the total sum of genera which represents strong affinity to tropical Asian flora. It is confirmed that the flora of Xishuangbanna is of the tropics in nature and as a part of the tropical Asian flora. Occurred at the montane habitats from northern margin of tropical Asia,the flora also shows conspicuous characters of the tropical margin and is the transitional to the subtropical flora of SW China. It is concluded that the flora of Xishuangbanna has the same origin as the floras of the tropical Guangxi and Hainan of S China and was possibly derived from the ancient Gandwana and Laurasian elements,but strongly affected by modern tropical Asian flora.