拟藁本属及近缘物种中国分类群花粉形态与质体基因组系统发育研究

Pollen Morphology and Plastome Phylogeny of Genus Ligusticopsis and Related Species in China

运用扫描电镜和光学显微镜对伞形科芹亚科拟藁本属8种及近缘类群2种(共10种)植物的花粉形态特征进行了观察与研究,并结合质体基因组系统发育树探讨拟藁本属的系统地位,提出分类处理意见,为拟藁本属的系统分类提供花粉形态学证据。结果表明:(1)显微观察显示,芹亚科拟藁本属及近缘类群10种植物花粉的极轴长与赤道轴长比值P/E为1.89~2.31,花粉大小变化范围25.45~41.70×11.29~20.52μm,花粉粒形态有近矩圆形、近矩圆-赤道收缩形、近长椭圆形和近长菱形4种,萌发孔位置皆为边孔。(2)扫描电镜观察发现,拟藁本属及近缘类群10种植物的花粉极面纹饰有条网、细孔网、细孔条网、平滑-细孔网、平滑穴网、条状6种类型,极面观有三裂圆形和三瓣形2种类型,属于伞形科较为原始至较为进化的花粉类型。(3)花粉形态学研究结果表明,拟藁本属的花粉形态均为近矩圆形型,扫描电镜下为条网状或细孔网状纹饰,属于一个较为自然的分类群,支持宜将拟藁本属从广义藁本属中独立出来单独成属,但蕨叶拟藁本的花粉形态为近长菱形,在芹亚科中属于较为原始的花粉类型。(4)分子系统发育分析表明,9个物种在亮蛇床部族内构成包含拟藁本属模式物种玉龙拟藁本在内的高支持率单系分支(Subclade A),且拟藁本属及近缘类群10种植物中的7个物种均位于该亚分支内,在质体基因组系统发育树中构成了拟藁本属的单系分支,即分子证据表明拟藁本的系统地位独立,且位于亮蛇床部族下,但蕨叶拟藁本独自形成了一个位于滇藁本分支的基出分支,表明其系统地位特殊,既不属于拟藁本属,也不属于藁本属。研究认为,拟藁本属为一年轻的由同一祖先分化的属,可能是起源于泛东亚的祖先种,在向西及青藏高原迁移扩散中,于东亚至中国-喜马拉雅地区快速辐射物种形成的;该研究建议将归叶拟藁本划入当归属,将细叶亮蛇床、毛藁本并入拟藁本属,将尖叶拟藁本并入藁本属中;蕨叶拟藁本的系统地位有待进一步研究。

The pollen morphology of eight species from Ligusticopsis and two species from its relatives(ten species in total)from Apiaceae subfamily Apioideae was observed and studied by scanning electron microscopy and light microscopy,combining with plastome phylogenetic tree to explore the phylogenetic status of Ligusticopsis and to propose advice on taxonomic treatment,aim to provide pollen morphological evidence for the systematic classification of Ligusticopsis.The results indicated that:(1)the pollen of ten species from Ligusticopsis and its relatives from subfamily Apioideae had a ratio of polar axis length to equatorial axis length(P/E)was 1.89-2.31,pollen size varied from 25.45-41.70×11.29-20.52μm,there are four types of pollen morphology:sub-rectangular,sub-rectangular-equatorially contracted,long sub-elliptical,and sub-rhombic,the apertures are all pleurotremes.(2)Scanning electron microscopy revealed that there are six types of polar sculptures:striate reticulate,thin perforated reticulate,perforated-striate reticulate,smooth pitted reticulate,smooth perforated reticulate,and striate;there are two types of pollen in polar view:trilobate-circular and inter-semilobate,which are the more primitive to the more evolved pollen types of the Apiaceae.(3)Pollen morphology shows that the pollen of Ligusticopsis are all sub-rectangular,with striate reticulate and perforated reticulate sculptures under SEM,making it a relatively natural taxon,which supported that Ligusticopsis should be an independent genus from“Ligusticum sensu lato”,but the pollen of L.pteridophylla is sub-rhombic,a relatively primitive pollen type in Apioideae.(4)Molecular phylogenetic studies show that nine species form a separate monophyletic branch(Subclade A)within Selineae containing the type species of Ligusticopsis(L.rechingerana),and seven species of ten species from Ligusticopsis and its relatives all located within Subclade A,which forms a monophyletic branch of the genus Ligusticopsis in the phylogenetic tree based on plastome,i.e.,molecular evidence for the phylogenetic independence of Ligusticopsis and its position is under Selineae,but L.pteridophylla forms a separate basal outgrowth branch in Hymenidium Clade,indicating that L.pteridophylla has a unique phylogenetic position and does not belong to either Ligusticopsis or Ligusticum.The results suggest that Ligusticopsis is a young genus that diverged from the same ancestor,possibly as a result of the formation of an ancestral species that originated in Pan-East Asia and spread westwards and across the Qinghai-Tibet Plateau,with rapid adaptive radiation in East Asia to the China-Himalaya region.In this study,it is suggested that Ligusticopsis angelicifolia should be placed into Angelica,Selinum wallichianum and Ligusticum hispidum should be transferred into Ligusticopsis,Ligusticopsis acuminata should be included in Ligusticum;further study is requested for the phylogenetic status of L.pteridophylla.