Morphology And Phylogeny Of Some Raphid Diatoms

The diatoms with raphe consists of Biraphidinales,Monoraphidales,Raphidionales and Aulonaphidinales,and they occupy a large proportion in freshwater.Diatoms are often classified by morphological characteristics.With the progress and innovation of research technology,the combination of morphological identification and molecular biology technology has become a necessary means for diatom research,which can not only enrich the biodiversity of diatoms,but also lay a foundation for the revision of population taxonomy based on a single system.In this study,A total of 44 monoclonal lines were establishedfrom water samples collected from mutiple places,including 2 classes,8 orders,13 families,20 genera and41 taxa,and SSU,LSU and rbc L genes were amplified and sequenced for the established monoclonal strains.The main conclusions of this paper are as follows:1.While SSU,LSU and rbc L genes were used to construct the phylogenetic tree,the monoclonal lines were identified by morphological means.Finally,the morphological data and molecular evidence were combined for comparative analysis.2.The morphological taxonomic data of 20 genera and the phylogenetic treeconstructed by SSU,LSU,rbc L,three gene series were combined to determine the relationships of large groups as follows :(1)Eunotia is the bottom branch;(2)The second group is composed of the genera Achnanthes,Nitzschia and Tryblionella.(3)The third group consists of Gyrosigma and Navicula;(4)The fourth group is composed of Mayamaea,Pinnularia,Halamphora,Rhopalodia and Selllaphora.(5)The fifth group is composed of the monophyletic groups,the genera Achnanthidium and Cocconeis;(6)Cymbella,Encyonema and Gomphonema are the genera at the top of the phylogenetic tree.3.The genus Eunotia is a separate group,belonging to the Eunotiales,which is consistent with the current morphological classification system;4.Molecular evidence divides the genus Achnanthes into the same group with the genera Nitzschia and Tryblionella,among which Nitzschia and Tryblionella belong to Bacillariaceae according to Cox or Round classification system.However,Achnanthes belongs to Achnanthaceae together with Platessa in Round classification system,and is listed as the only genus of Achnanthaceae in Cox classification system.This result is consistent with Cox classification system.In the classification system of freshwater algae in China,it is suggested that the genus Achnanthes should be regarded as the only member of the family Achnanthaceae,and the suborder of Achnanthaceae should be listed separately.In view of this,we believe that firstly,the genus Achnanthes can still be classified as a monoraphid diatom according to morphological classification characteristics.Second,a separate suborder of the genus can effectively explain the phenomenon that the genus is grouped into a single branch with the Bacillariaceae in molecular data.5.Gyrosigma and Navicula belong to Naviculinceae in the Cox classification system,but belong to Pleurosigmataceae and Naviculinceae respectively in the Round classification system,which is more consistent with the results in the Cox classification system.6.Mayamaea,Halamphora,Pinnularia,Rhopalodia and Sellaphora are divided into a group.Although each branch has a high support rate,there is still a lack of intermediate diatom data to supplement in morphological observation.7.Achnanthidium and Cocconeis constitute the monoraphid diatoms group,and the monoraphid diatoms group is closely related to the group composed of Cymbella,Encyonema and Gomphonema,which is supported by the four phylogenetic trees constructed from SSU,LSU and rbc L genes.Combined with the results of morphology and molecular systematics,the evidence of molecular systematics basically supports the classification system based on morphology,and the classification conclusions of the two are basically consistent at the genus and species levels.