Extremely variable, 6-60 cm high, dark green, commonly reddish-tinged, loosely or densely tufted or forming open colonies, rarely erect, more often decumbent or prostrate and rooting, or occasionally floating; rhizomes usually short with short internodes or occasionally long and giving rise to mat-like colonies. Leaves terete to ± compressed with transverse septa ± visible externally. Inflorescence very variable, 1-15- (40) cm long. Flowers in small dark brown clusters of 4-8 at tips of branchlets. Tepals 2.5-3 mm long, all ± equal, acute. Stamens 6. Capsule 2.5-3.5- (4) mm long, > tepals, ovate-oblong, trigonous, acute, upper third tapering to a distinct mucro, glossy, dark brown to black.