Cyperus javanicus is characterized by simple leaves that are usually more numerous and longer than the culm. The leaves are linear, 8–12 mm wide, with a plicate structure below the middle and flat or inrolled margins above the middle. The surfaces are green, glaucous, and often white-powdery, and the blades are coriaceous. Leaf margins are prominently scabrous. The sheaths are dark brown or purplish brown and septate-nodulose, with no stipules present. The flowers are organized in umbelliform inflorescences, compound or partially so, measuring 10–15 cm in length. The inflorescence features 6–10 rays, each up to 12 cm long and spreading. Secondary rays, when present, number 3–6, and the spikes are cylindrical to oblong, 1.5–3 cm long and 8–12 mm wide, bearing numerous spikelets. Involucral bracts number 5–6, with the lower ones much longer than the inflorescence itself. Spikelets are 5–7-flowered, grayish brown, white-powdery, divergent to slightly reflexed, turgid, and lanceoloid to oblong-lanceoloid, measuring 4.5–6 mm in length and 1.8–2 mm in width. The rachilla is broadly winged and jointed above the prophyll. Glumes are brown with reddish-brown flecks or lines, subcoriaceous, broadly ovate, 2.8–3 mm long and 2 mm wide, with many nerves and whitish-hyaline margins. The flowers are bisexual (perfect) and lack a corolla (petals). There are three stamens and a superior ovary. The achenes are blackish brown, ellipsoid-obovate, trigonous, about half as long as the glume, and minutely puncticulate. Each plant produces one seed, with a thin seed coat, free from the pericarp. The embryo is basal, and the endosperm is abundant. It occurs in marshes and taro paddies, as well as along streams and ditches, coastal pastures, rocky coastal sites and cliffs at elevations ranging between 0-180 meters.