The genus Pleioblastus is a complex group of Southeast Asian temperate bamboos with 7-21 species, depending on taxonomic authority. This study tests the hypothesis that taxonomic complexity in this group is due in part to hybridization and subsequent backcrossing in natural populations, resulting in a reticulate evolutionary history and a contemporary species assemblage that includes cryptic hybrids. This hypothesis is supported by recent research on the temperate bamboos that revealed intergeneric hybrids involving Pleioblastus and other genera of temperate bamboos (Triplett and Clark, 2021). The objective of the current study was to use data from Amplified Fragment Length Polymorphism (AFLP) markers and a combination of tree-building and ancestry assignment analyses to test the hypothesis that Pleioblastus section Nezasa is a mix of parental and hybrid lineages. This research is valuable for understanding the evolutionary history of this important group of forest grasses, which in turn will inform the classification and nomenclature of the species. A better understanding of the group also has implications in conservation due to hybridization-induced extinction, since assessing species boundaries is a necessary first step to establish the need for potential conservation efforts. The data revealed 2-3 major lineages (Nezasa 1, Nezasa 2, and Nezasa 3) and cryptic hybrids within and among these lineages, thus supporting the hypothesis that hybridization had an important role in the evolution of Pleioblastus. This research provides a stepping-stone for resolving bamboo taxonomy, including the East Asian relatives of Arundinaria (including Pleioblastus sensu lato and Pseudosasa), and other hybrid swarm systems. The broader implications of this research for our understanding of plant evolution and species nomenclature are discussed in the context of grass phylogenetics and evolution
