Phylogenetic estimation and morphological evolution of Alsineae(Caryophyllaceae)shed new insight into the taxonomic status of the genus Pseudocerastium

Pseudocerastium is a monotypic genus in Caryophyllaceae endemic to China.The genus has been widely accepted since it was described in 1998,however its phylogenetic position within Caryophyllaceae has never been studied.In the present study,the whole plastid genome and nuclear ribosomal internal transcribed spacer(ITS)sequences of Pseudocerastium stellarioides was obtained through genome skimming,and the phylogenetic position of the species was studied for the first time.Plastid phylogenomic analysis of Caryophyllaceae revealed that Pseudocerastium is clustered within the tribe Alsineae with strong support.Phylogenetic analyses based on an enlarged taxon sampling of Alsineae using five DNA regions(matK,rbcL,rps16 intron,trnL-F and ITS)revealed that P.stellarioides was nested deeply within Cerastium with strong support.Analyses of morphological character evolution suggest that the ancestral states in Alsineae include three styles and a six-lobed capsule at the apex,while both Cerastium and Pseudocerastium have five styles and ten lobes at the apex of the capsule,further supporting their close relationship.The species Pseudocerastium stellarioides is similar to Cerastium wilsonii in morphology,but differs in having villous indumentum on the lower part of the filaments and compressed globose seeds.Therefore,based on the present molecular and morphological evidence,the generic name Pseudocerastium is reduced here as a new synonym of Cerastium and the species P.stellarioides is transferred to Cerastium as C.jiuhuashanense.

基于多个叶绿体基因序列片段重建广义苋科系统发育关系

苋科(Amaranthaceaesensulato)是石竹目(Caryophyllales)第二大科,目前被普遍接受的苋科为其广义概念,含狭义苋科(Amaranthaceae sensu stricto)和藜科(Chenopodiaceae)。然而到目前为止,藜科是否应作为独立的科还存在争议。此外,广义苋科内部各亚科之间的系统关系也尚未厘清。对广义苋科所有13个亚科代表类群进行取样(共59种),基于8个叶绿体序列片段重建其系统发育关系,并结合分子钟估算,对该科及其主要分支的起源与分化时间进行推测。结果表明,广义苋科与狭义苋科都是很好的单系,但藜科并非单系,因此不支持藜科在科级水平的地位,支持广义苋科的观点。除了多节草亚科(Polycnemoideae)之外,其它亚科的系统位置均得到很好的分辨。分子钟估算结果表明,广义苋科于白垩纪晚期约69.9Ma分化出该科的2个主要分支,且该科在白垩纪-古近纪边界附近时期(约66.0Ma)可能发生过快速辐射分化事件。