A very abundant desmids biota was found in Zhalong National Nature Reserve in 2011-2012,including 90 taxa in total.Among them,a Pleurotaenium species is proposed as new to science,Pleurotaenium parvulum Li,Fan&Wei.The new species is characterized of small cells and a long cylinder without processes,a truncated apex,five small nodules on cross section,cell wall smooth or with puncta,semicells with two axial longitudinal ridge-shaped chromatoplasts,and each with two pyrenoids.Differences between the species and allied taxa are discussed.