中文摘要：

粗茎秦艽Gentiana crassicaulis Duthie ex Burk和西藏秦艽G.tibetica King ex Hook．f．的主要区别是前者花冠小、檐部蓝色，后者花大、檐部紫褐色；但二者在西藏东南部地区的形态界限不清楚，具有较多的中间形态过渡类型。本文以该地区居群作为主要研究对象，并以云南和西藏其他地区的典型形态类群为对照，比较研究了两个物种间的形态学、染色体和分子标记界定。共研究了10个居群69个个体的trnS—G和ITS序列、6个居群26株植株的染色体倍性和54份标本的形态变异。结果表明，花冠大小与染色体倍性密切相关。云南等地分布的粗茎秦艽均为二倍体（2n=26），花冠较小；西藏西部的西藏秦艽均为四倍体（2n=52），花冠较大。而西藏东南部的形态过渡类型也为四倍体，花冠较大，且其中的部分植株花颜色变浅，类似西藏秦艽。但母系与双亲遗传背景的分子标记都表明西藏东南部居群与典型形态特征上的粗茎秦艽聚为一支，应属于粗茎秦艽；ITS序列上也未发现杂合位点。这些分子证据都不支持近期杂交渗入造成形态过渡性的假设。综合分析表明多倍化造成了粗茎秦艽种内形态特征的变异，其四倍体个体与四倍体西藏秦艽在形态特征上的趋同，最终导致了二者在西藏东南部地区形态界限的模糊。但是．分子证据可以很好地区分这种多倍化造成的形态趋同。我们的研究结果还表明，综合利用分子、染色体和广义形态证据来解决近缘种之间种范围的界定具有更大的优势。此外，还讨论了粗茎秦艽不同染色体倍性的分布以及该高山物种可能的起源与扩散途径。

英文摘要：

Gentiana crassicaulis Duthie ex Burk. and G tibetica King ex Hook. f. are confusing gentians. The former has smaller corolla and blue-purple limbs whereas the latter has larger corolla and purple-brown limbs. Intermediate types are often found in southeast Xizang where both species are putatively considered to occur. A question has been raised whether these intermediate types were produced by introgression between the two species, which further contribute to the taxonomic ambiguity. In the present study, we comprehensively compared morphological variations, chromosome numbers, and sequences of two DNA fragments from populations of the intermediate types and those of the two typical species. We sequenced cpDNA trnS-G and nuclear ITS fragments of 69 individuals of 10 populations, counted chromosome number of 26 individuals of six populations and measured morphological variation of 54 specimens. We found that corolla size is highly correlated with ploidy level. The populations of typical G crassicaulis from Yunnan were diploid （2n=26） with small corolla while those of G tibetica from western Xizang were tetraploid （2n=52） with large corolla. The populations of the intermediate types from southeast Xizang were tetraploid with large corolla, and a few individuals with purple to brown limbs. These features suggest that the intermediate types show more similarities to G tibetica. However, DNA sequence evidence unambiguously grouped those populations with G crassicaulis. Both nuclear and chloroplast DNA showed consistent results： the intermediate populations showed identical cpDNA and very similar ITS sequences to typical G crassicaulis. No sequence variation beyond what occurred in typical G crassicaulis and G tibetica was found from multiple individuals of the intermediate types. Thus the hypothesis of a recent introgression or hybridization between the two species could be rejected. Our results demonstrated that polyploidization had contributed to the intraspecific variation in G crassicaulis and that the te