Morphological and phylogenetic analysis of a new Melosira species and revision of freshwater Melosira in China

Melosira is one of the most common diatom genera found in freshwater ecosystems.There are many freshwater species of Melosira,of which M.varians is the most common.In our investigation of periphytic diatoms in the Jinsha River,China,a new species,M.capsularum sp.nov,was characterized in combined morphological and molecular approaches.M.varians was also analyzed using molecular data.The new species is similar to M.varians,M.moniliformis,M.nummuloides,and M.lineata in morphology.The cells are capsular and join to filaments by mucilage pads that are secreted on the valve face and united into pairs by their cingula.The valve face is domed and covered with small granules,and the valve mantle edge has a milled appearance.The two strains of M.capsularum are in a single clade obviously away from other Melosira species,as determined in phylogenetic analysis based on nuclear small subunit(SSU)rDNA sequences and the chloroplast-encoded rbc L gene.Thus,the results of morphological comparisons and phylogenetic analysis based on molecular data provide strong evidence that M.capsularum is a new species,thereby increasing the total number of recognized freshwater diatom species in China.In addition,we have systematically reclassified the freshwater Melosira that have been recorded in China.