喀喇昆仑山-西昆仑山地区十字花科植物的生态地理分布和区系特点

THE ECO-GEOGRAPHICAL DISTRIBUTION AND THE FLORISTIC CHARACTERISTICS OF THE FAMILY CRUCIFERAE FROM KARAKORUM-WEST KUNLUN AREA IN CHINA

喀喇昆仑山—西昆仑山地区位于我国西部边疆,约占北纬33°—39°、东经74°—83°,是青藏高原西北隅及北部边缘的高山、高原区。本区的十字花科植物就目前所知有30属66种。从垂直分布的情况来看,大多数种都分在高山地带。其中海拔4000—5000m的高山荒漠地带有32种,占本区总属数的49%;海拔4800—5600m以上的冰缘湿地何12种,占18%;海拔2600—4000m的山地荒漠地带有15种,占23%;海拔2600—3800m的针叶林下及林缘草地有8种,占12%。表明本区十字花科值物是以寒旱生的高山、高原分布类型为主,而以中低海拔及荒漠旱生类型为次。水平分布方面,本区西部分布有49种,并以中亚成分为主;而东部和南部有28种,其中青藏高原成分较多,从属的分布区类型来看,本区的十字花科植物全都是温带性质的。其中,北温带分布类型占总属数(世界分布不计算在内,下同)的28%;其次是地中海、西亚至中亚和中亚分布类型各占21%;而东亚分布类型(全都是中国—喜马拉雅亚型)占10%。本区十字花科植物的区系特点如下:1.种类贫乏,分布广泛;2.特有种炎缺乏;3.地理成分混杂;4.同周围区系联系广泛,但同西藏区系的关系最为密切。

Karakorum-west Kunlun area is situated at the westmost of China, the square between 33°-39°N and 74°-83°E, extending to theNorthwestmost of Qinghai-Xizang (Tibet) plateau. This area belongsto the alpine and highland region. It contains 30 genera and 66 speciesof Cruciferae. The majority of species are distributed over the alpinezone. Among which summed up to 32 species (about 49% Cruciferaetotal ofthis area) occur in the alpine desert zone between 4000m and5000m alt.. Where there are 12 species (about 18% of the totalCruciferae) occur in the damp region of close to the glacial fringeand the snow line (4800-5600m alt.). Where there are 15 species(about23%) occur in the mountain desert region between the altitude 2600 mand 4000 m. Only 8 species (about 12%) occur in the coniferous forestand the grassland near the forest fringe. The analysis of the verticaldistribution indicated that Crucifer flora is primaryly alpine typebelonging to the cold resistant plant, Otherwise secondary xerophytesin the lower altitude. In the west part of this area, there are 49 spe-cies of Crucifer and are chifly the Central Asia elements. In the eastPart of this area, there are 28 species and the elements of Qinghai-Xizang plateau occur more. The distribution-type of genera is all oftemperate nature. Among them, that of North temperate has percen-tage of 28% of total genera (The cosmopolitan genera are excludedfrom the total and from the calculation of the other statics.)and thatof Mediterranean. Western Asia to Central Asia and Central Asia hasa respective percentage of 21% of total genera. And that of Eastern Asia(all of Sino-Himalaya subtype) has a percentage of 10% of total ge-nera. The floristic characteristics of the family Cruciferae in this areaare as follows: (1) Species are poorer, but they are wide spread. (2)Lack endemic species. (3) The geographical elements are mixed. (4)This flora is closely related to the flora of Xizang, and connects exten-sively with around areas.