In this paper, four taxa are reported from Hainan Island, south of China, including Frustulia soror
Graeff & Kociolek, Decussiphycus placenta
(Meister) Guiry & Gandhi, Rhopalodia contorta
Hustedt, and Frustulia splendida
Hustedt. Among these taxa, the first three are new records to China. Except for Frustulia soror
, the other three taxa lack scanning electron microscopy (SEM) data as they were reported decades ago. In this research, light microscopy (LM) and SEM were used to observe these taxa, with detailed morphological descriptions and habitat characters given. Important morphological and biogeographical data on these species were also provided.