Аннотация:The Eunotiales are characterized by having both a raphe system and rimoportulae, and have been thought to occupy an important position in the evolution of raphid diatoms from both morphological and molecular points of view. During the investigation of the diatom flora of south-central China and Vietnam, a new genus of freshwater diatoms Sinoperonia Kociolek & Liu was observed from both countries. It has wedge-shaped frustules, a raphe valve with a well-developed raphe system in the middle and rimportulae near the apices, and a rapheless valve with only rimportulae near the apices. These characters showed it belong to Peroniaceae, Eunotiales. But this genus differs from Peronia by not having small raphe branches in any of the valve; and the internal opening of the rimoportulae is not a typical lip-shaped structure with a thickened siliceous border, but slit-like at the same level with the valve. Based on our observation this diatom has incredible morphological variation, since it can develop monoraphid, biraphid and araphid valves, in the general proportions of 4:2:1, respectively. The proportion suggested that this genus is a “monoraphid” genus, and represents another special lineage of the Eunotiales. The ability of it to produce biraphid, monorapid and araphid frustules also provides a unique insight to producing raphe and rapheless valves. We discuss the extreme degree of morphological variation in this new taxon, and the growing body of evidence suggesting the freshwater diatom flora of China may harbor many endemic genera as well as species.