Abstract
A new genus of Arundinarieae, Khoonmengia, is established to accommodate a unique new bamboo species, K. honbaensis, from central-southern Vietnam. The morphological features, habitats and distribution of Khoonmengia and related genera, i.e. Ampelocalamus and Hsuehochloa, are compared. The characters of its scrambling habit, internodes with brownish green dots, conspicuous nodes swollen at one side, elliptic buds wholly sunken into culm, extravaginal branching pattern, mid-culm branch complement with one central dominant branch elongating to reiterate the culm accompanied by several lateral slender branches, swollen culm sheath base with a distinctive zone of transverse wrinkles, synflorescence composed of only one spikelet, single or several to many synflorescences arranged into a raceme or panicle terminal on leafy branches, purple anthers and nut-like caryopsis with hardened pericarp and loosely adherent lemma and palea distinguish K. honbaensis from morphologically similar taxa. In order to investigate the phylogenetic position of this unknown bamboo, molecular phylogenetic analyses based on the nuclear gene GBSSI were also conducted, and the results proved that K. honbaensis is definitely a member of Arundinarieae with an isolated position, which also indicated that this species could not be assigned to any of the already described genera and supported the establishment of the new genus.