A perennial plant up to 120 cm high; stem square and smooth. Leaves in whorls of 6-8, approximately 1/2 to 1 1/4 inches long by 2 to 4 mm wide, one-veined, with small forwardly-directed prickles along the edges, and ending in a short point. Flowers produced in clusters on a flower stalk that arises from the area between the stem and leaves (leaf axils); consist of 4 white petals. Fruits 2-parted capsule that separates at maturity.