Willdenowia teres is a clumped, rhizomatous perennial, 0.3–1 m high. The leaves or culms are smooth and sparsely branched, with sheaths loosely wrapped around the culm, the upper third membranous and decaying on the older culms. 

The plant is dioecious - male and female inflorescences occur on different plants. On the male plant the inflorescence has indefinite spikelets branching into racemes, partially enclosed in a large spathe (leaf like bract that encloses a flower cluster), 10–60 mm long, 9–20 mm wide. In the female plants, the inflorescence is linear,  25–110 mm long and 4–15 mm wide, with 1 or 2–5 spikelets. The spathes are as long as the spikelets or even sometimes longer. Female spikelet is 7–10 mm long, with a fleshy pedicel. The fruit is a smooth, dark brown nut, sometimes sparsely pitted with an obvious elaoisome (fleshy green structure attached to the seed). The flowering season is mainly from July to October. The seed is released from November to June.