利用叶绿体DNAtrn L-F序列初步探讨菊科风毛菊属的系统发育

A preliminary investigation on the phylogeny of Saussurea (Asteraceae: Cardueae) based on chloroplast DNA trnL-F sequences

风毛菊属SaussureaDC .是菊科物种分化十分剧烈和分类处理十分困难的一个属。该属的单系起源性质、属下分类系统以及一些独特形态物种的系统位置尚不清楚 ,有待进一步验证。本文测定了代表该属 5个亚属 37种植物 43个样品和川木香属DolomiaeaDC .的 1种样品的叶绿体DNAtrnL_F序列 ,并调取菜蓟族CardueaeCass.与风毛菊属具有一定亲缘关系的 1 3属的该序列 ,一起进行了分支分析 ,重点验证该属的属下形态分类系统以及形态特殊、青藏高原地区特有的雪兔子亚属subgen .Eriocoryne中假雪兔子组sect.Pseudoeriocoryne的单系性质。研究结果表明 :( 1 )尽管风毛菊属 5个亚属形态变异极大 ,但种间的trnL_F碱基变异却非常小 ;( 2 )根据形态学划分的 5个亚属在分支图上没有得到分辨 ;( 3)根据无明显茎、叶呈莲座状包被头状花序等特征建立的假雪兔子组是一多系群 ,与其他雪兔子亚属的种类也没有密切的亲缘关系 ,其共同拥有的形态学特征分别起源了 4次 ;( 4 )雪莲亚属假雪莲组subgen.Amphi laenasect.Pseudoamphilaena中的多鞘雪莲S .polycolea变种尖苞雪莲S .polycoleavar.acutisquama与风毛菊亚属subgen .Saussurea的长毛风毛菊S.hieracioides、美丽风毛菊S .superba、打箭风毛菊S .tatsienensis和重齿风毛菊S .

Saussurea DC., a highly diversified genus with about 400 species in the Asteraceae, has been an extremely difficult group in both taxonomical and phylogenetic studies. The monophyletic origin, infrageneric classification and systematic positions of some species with unique gross morphology remain unclear for this genus. The main aim of this study was to examine infrageneric relationships of Saussurea as inferred from molecular evidence against the existing supraspecific classification on the basis of the morphological characteristics. In addition, we intended to use phylogenetic analyses of DNA sequence data to investigate systematic position and relationship of each species in sect. Pseudoeriocoryne (subgen. Eriocoryne) and test the monophyly of this section, which is likely to be established based on the morphological characters with convergent evolution. We sequenced chloroplast DNA tmL-F for all four species of sect. Pseudoeriocoryne and other 33 species, which represent the recognized five subgenera in Saussurea, and conducted a phylogenetic analysis together with 14 related genera in the Cardueae Cass. The variation of trnL-F sequences is very low among the sampled species in spite of their extremely diverse morphology. Five subgenera in Saussurea delimitated based on morphological characters were unrecognized on all most parsimonious trees. Sect. Pseudoeriocoryne is a polyphyletic group, and the four species in this section were found to be distantly related to each another, and showed no close relationship with the other species in subgen. Eriocoryne. The morphological characters to circumscribe this section had separately evolved four times. An 18-bp insertion was identified for S. polycolea var. acutisquama in sect. Pseudoamphilaena of the subgen. Amphdaena and other four species, S. hieracioides, S. superba, S. tatsienensis and S. katochaete from the subgen. Saussurea. This long and unique insertion was only recognized for these five species in the total Cardueae, and it must have evolved before the morphological diversification of this species complex. However, this insertion was not found in S. polycolea and another population of S. katochaete. Therefore, the insertion found in S. polycolea var. acutisquama and S. katochaete might have resulted from haplotype introgression or retaining because of hybridization. This study demonstrates for the first time that species even within a genus had also undergone convergent evolution in their morphology under the same ecological selection pressure of the Qinghai-Tibet and habitats. This implication is especially important for those researches, which study relationships of the species distributed there and name taxonomical entities based exclusively on the gross morphology. In addition, our preliminary results indicate that Saussurea provides a typical case for studying rapid speciation, reticulate and convergent evolution under the arid habitats.