Flowering material of Ferrocalamus rimosivaginus has been identified, allowing its analysis and description. The unit of inflorescence of the synflorescences of F. rimosivaginus is panicle-like and its fruit is berry-like. Ferrocalamus rimosivaginus differs from F. strictus in its rachilla puberulent except on its adaxial surface, the first glume with a glabrous apex, the abaxially glabrous lemma with an acute mucronate apex, and the palea with the surfaces between keels apically pubescent and progressively less pubescent towards the glabrous base. An epitype is designated to support the sterile holotype.