| Cymbellaceae belongs to Bacillariophyta,Bacillariophyceae,and Cymbellales,which is a natural group with rich species.At present,there are more than 4000 taxonomic units of the family Cymbellaceae reported in the world,and more than 400 taxonomic units have been reported in China.In the traditional taxonomic study of Cymbellaceae,the most prominent taxonomic feature of this group is the asymmetry of the apical axis,which is usually dorsiventral;The main basis for identification is the shape of valves,the striae,the raphe and the stigma.However,the differences between some different species in the same genus are subtle and the identification is difficult.In this paper,light microscope and scanning electron microscope were used to observe and categorically identify the morphological and structural characteristics of the isolated and cultured species of Cymbellaceae,and to explore the morphological and taxonomic characteristics of the family.In parallel,sequencing analysis of 18 S rDNA,28 S rDNA,rbcL and psbC gene sequences was performed on the isolated and purified algal strains,and the relationships among each genus and among various species of the genus were further analyzed by constructing single gene and multigene molecular phylogenetic trees by Maximum Likelihood and Bayesian Inference techniques.The main results are as follows:1.Approximately more than 400 taxa have been reported for the diatoms of the Cymbellaceae in China.We have collated the reported cases of Cymbellaceae from various regions of China;2.65 strains were isolated.These are identified as 8 genera and 19 taxa including7 taxa in Cymbella,9 taxa in Encyonema,1 taxa in Cymbopleura and 2 taxa in Qinia.Morphological descriptions of these species are provided,with illustrations;3.Based on Gen Bank,the published molecular information of Cymbellaceae has been sorted out.Cymbella has 212 sequences;Cymbopleura has 32 sequences;Encyonema has 116 sequences;Encyonopsis has 8 sequences;Karthickia has 5sequences;Placoneis has 54 sequences;Reimeria has 8 sequences(as of 2023.02.28).In this study,235 species sequences of Cymbellaceae have been obtained,and 112 sequences have been submitted to Gen Bank;4.Selecting 23 morphological characters to construct morphological phylogenetic trees for 22 genera of Cymbellaceae.Using four gene sequences of 18 S rDNA,28 S rDNA,rbcL and psbC,two phylogenetic trees were constructed: Maximum likelihood(ML)and Bayesian inference(BI).The main results are as follows:(1)The morphological phylogenetic tree shows that Alveocymba and Cymbopleura are the more primitive genera of the family Cymbellaceae,and Cymbella and Kurtkrammeria are the more advanced genera;(2)The topological structure of the phylogenetic tree jointly constructed by single gene and multiple molecular markers supports morphological identification,and there is a strong relationship among the genera.It is found that Seminavis,Encyonema and Placoneis are all monophyletic groups,and the information of Reimeria species samples is comparatively less,but the current research shows that it may be a monophyletic group.At the same time,Cymbella,Cymbopleura and Encyonopsis formed multiple branches,and the three may be multiphyletic groups;(3)Different clades of Cymbella are associated with different groupings within the genus.Combined with morphological analysis,this study found that the tumidula/mexicana group often clustered into two branches,one was Cymbella tumida,and the other included Cymbella mexicana and Cymbella janischii,which clustered with Cymbella proxima as sister clades;Cymbella aspera clustered as one branch,consistent with the morphological grouping;5.18 S rDNA,28 S rDNA and rbcL genes were used to construct Maximum likelihood tree(ML)and Bayesian inference tree(BI).Based on the combination of morphology and molecular phylogenetics,the results show that three of the strains we studied belong to two species of the genus Qinia,two of which belong to a proposed new species Qinia hubeii Liu & Kociolek sp.nov.;another new species is Qinia wuhanensis Liu & Kociolek sp.nov..On the phylogenetic tree,the two are sister branches and have a close relationship with the Encyonopsis.Our study supports that Qinia hubeii Liu & Kociolek sp.nov.and Qinia wuhanensis Liu & Kociolek sp.nov.represent an independent genus,Qinia,whose morphologically most obvious feature is that the apical pore field is bisected by the distal end of the raphe and the areolae are elliptic with projections that occlude the openings,giving the appearance of a “C” shape.Qinia forms a large branch with Encyonopsis,Cymbella,and Cymbopleura,and Qinia is closely related to Encyonopsis.This study provides reference data for the classification and molecular research of Cymbellaceae. |
