One of the more distinctive morphological characters of Schoenus brunnescens is the brown culm bases of this species, compared to the more reddish ones of the majority of southern African Schoenus. A second species of southern African Schoenus that has brown culm bases is Schoenus bracteosus; however, that species has firm primary inflorescencebracts that enclose its spikes — a character absent from S. brunnescens.
Similar to Schoenus compactus and Schoenus crassus, S. brunnescens has straight and stiff basal culm leaves (i.e. leaves at the base of its flowering stems). However, the culm bases of S. compactus and S. crassus are generally more reddish-brown compared to the ones of S. brunnescens. In addition, the spikelets of S. compactus and S. crassus are generally longer and the nutlets larger compared to those of S. brunnescens.