Perennial. S. achtenii is distinguished from S. unguiculata by its broader leaves, fewer lateral panicles, very faintly reticulate-lacunose, sparsely white-hirsute achenes and by its small trilobed hypogynium with the lobes often 2-3-fid. not unguiculate.
Lateral panicles pendulous on long slender peduncles
Perennial up to 2 m. high with swollen stem-bases
Perennial. Rhizome little more than the connective between ± contiguous culm bases or elongate with culms arising at intervals of up to 15 mm; scales reddish-brown. Culms 0.7-1.10 m tall, glabrescent or sparsely villous-hispidulous. Leaves 2.5-5 mm broad, villous on abaxial ribs and sheaths, glabrous adaxially and below mouths of sheaths; mouths convex with a membranous margin 1 mm long, the margin base villous. Inflorescence with terminal panicle up to 90 mm long, smaller lateral panicles single at 1-3 nodes exserted up to 180 mm from sheaths. Bracts foliaceous. Male spikelets sessile or shortly pedicillate, 7-9 mm long; glumes stramineous or reddish-striate, glabrous. Female glumes similar, shortly awned. Achenc obovoid to subglobose, 2.5-3 x 1.8-2 mm, hairy, lightly and obscurely lacunose, grey or brownish-grey, hairs white: hypogynium small with 3 acuminate, acute, or bifid lobes, white.