The genus Gelidocalamus T. H. Wen, endemic to southern China, is a small but taxonomically problematic genus of Arundinarieae (Poaceae, Bambusoideae). During field work, a population of Gelidocalamus from Zixing, Hunan, was discovered, appearing to be distinct from our previously identified collection. Comparisons of the population of Zixing were performed by using scanning electron microscopy (SEM) and a plastid genome-based phylogeny. Morphologically, it was mostly similar to G. multifolius, but differed by culm leaf erect with densely white pubescence, apical branch sheath much longer than the internodes and foliage leaf larger. Phylogenetically, the new species was well-supported as a sister to the clade of G. multifolius + G. tessellatus, and the above three taxa were clustered in the Shibataea clade (IV) of Arundinarieae. Thus, the new species, formally named as Gelidocalamus zixingensis W.G.Zhang, G.Y.Yang & C.K.Wang, was described and illustrated herein.

Based on several sources of evidence from morphology, the micromorphology of the abaxial leaf epidermis, and a phylogenetic analysis using complete chloroplast genome data, a new combination and two new synonyms are reported in the genus Indocalamus Nakai. Indocalamus cordatus T. H. Wen et Y. Zou is synonymized with I. tessellatus (Munro) P. C. Keng, and I. chebalingensis W. T. Lin is synonymized with I. multinerus (W. T. Lin et Z. M. Wu) W. T. Lin. As a new combination, I. mollis (H. R. Zhao et Y. L. Yang) L. Q. Gao, W. G. Zhang et G. Y. Yang was created and is supplementally described. In addition, the lectotype of I. multinerus is designated herein.

Based on several evidences from morphology, micromorphology on the abaxial leaf epidermis, and phylogenetic analysis by using complete chloroplast genome data, a new combination and two new synonyms were reported in the genus Indocalamus Nakai. Indocalamus cordatus T. H. Wen et Y. Zou was synonymized with I. tessellatus (Munro) P. C. Keng, and I. multinerus (W. T. Lin et Z. M. Wu) W. T. Lin was synonymized with I. chebalingensis W. T. Lin. As a new combination, I. mollis (H. R. Zhao et Y. L. Yang) L. Q. Gao, W. G. Zhang et G. Y. Yang, was created and supplementally described. In addition, the lectotype of I. chebalingensis was designated from several syntypes.

Indocalamus Nakai, a genus within the tribe Arundinarieae, has significant horticultural and economic value. However, its classification has long been challenging, and due to limited sampling, both intra- and intergeneric phylogenetic relationships, as well as its evolutionary history, remain unclear. In this study, extensive field surveys and comprehensive sample collection were conducted to address these challenges. A total of 31 complete plastomes of Indocalamus species were assembled. All plastomes exhibit a typical quadripartite structure, ranging in length from 139,555 bp to 139,791 bp, and contain 137 genes, including 90 protein-coding genes, 39 tRNA genes, and 8 rRNA genes. Phylogenetic analyses indicate that Indocalamus is polyphyletic and divided into three distinct clades (IV, V, and X). Based on integrated phylogenomic and morphological evidence, we propose a revised classification of Indocalamus into three major sections. Fossil-calibrated divergence estimates reveal that the major clades of Indocalamus are not monophyletic, highlighting a complex reticulate evolutionary history exemplifying the widespread rapid radiation observed in temperate woody bamboos. The intensification of the East Asian monsoon is likely to have played a key role in driving the rapid radiation of these lineages. Additionally, several clade-specific DNA barcodes (trnT-trnE, petN-trnC, petA-psbJ, and petD-rpoA) were identified, which will enhance the identification of Indocalamus and its closely related genera. This study, through extensive sampling and integration of morphological and molecular phylogenetic evidence, provides a preliminary delimitation of the genus Indocalamus, elucidates its complex evolutionary history, and lays a solid foundation for future systematic research and horticultural applications.