Annual; culms 5-90 cm high, ascending. Leaf-blades 2-25 cm long, 2-7 mm. wide. Panicle 2-15 cm long; involucres ovoid, 4-11 mm long; inner spines flattened, connate at the base to form an ovoid or diamond-shaped disc 2-4 mm across, bearing 1-3 shallow grooves on the outer face, ciliate below, retrorsely barbellate and mostly pungent at the tip; outer spines numerous, acicular, shorter than the inner, commonly divergent, rarely suppressed. Spikelets 1-3 per burr, 3.5-6 mm long.