Cyperus trachysanthos is a perennial plant with short rhizomes and densely tufted culms that are obtusely trigonous, measuring 20–45 cm in height and 1.5–2.5 mm in diameter, and possessing a viscous texture. The plant has simple, three-ranked leaves with linear blades that are longer than the culm, 2.5–3.5 mm wide, and feature a septate-nodose, channeled structure. The leaves have a green, glaucous, and subcoriaceous surface with remotely toothed margins and parallel veins. The leaf apex is gradually narrowed and long-acuminate, and the sheaths are yellowish-brown with a hyaline ventral side that is reddish-brown. The flowers are simple corymbs, 5–9 cm long and 6–12 cm wide, with 1–5 rays each bearing 2–6 heads of spikelets that are 1.5–2.5 cm in diameter. There are 3–5 involucral bracts that surpass the corymb, and the spikelets, numbering 10–30 per head, are 8–20-flowered, pale yellowish-brown, lanceolate-ovate, flattened, 8–12 mm long, and 3–5 mm wide. The rachilla is winged, and the glumes are pale yellowish-brown to pale reddish-brown, chartaceous, broadly ovate, 3–3.5 mm long, and about 2 mm wide, with an acute apex and a broad green, glaucous keel that prolongs into a recurved mucro. The flowers are bisexual (perfect) but lack petals. The fruit consists of dark brown, obovoid to narrowly obovoid, trigonous achenes, approximately 1.5 mm long, puncticulate, with an acute apex. Each achene contains one seed, which has a thin coat, free from the pericarp, a basal embryo, and abundant endosperm. It is found in wet environments like pond margins and wet slopes, at elevations ranging from 3-160 meters.