Pseudosasa nanunica , a bamboo endemic to Guangdong and Hunan provinces, China, has a complicated taxonomic history due to lack of information on its floral morphology. It was initially described as a member of Indocalamus , and later successively transferred to Pseudosasa , Arundinaria and Acidosasa by different researchers. With the newly collected reproductive materials, we confirmed that this species is characterized by having branch complement with 1–3 branches per node, branch base appressed to the culm, narrowly trullate culm bud, panicle-like unit of inflorescence of the synflorescence and each floret with three stamens and three stigmas, which match well with the diagnostic characters of Pseudosasa . After comparison with similar congeneric species, we concluded that it is a distinct species of Pseudosasa . A supplementary description on its floral morphology as well as two color plates and a diagram of its synflorescence is also provided.