Cyperus xanthus is a perennial herb with a base encircled by a few fibers from remaining old leaves. The rhizome is robust, reaching up to 2.5 cm in diameter, obliquely extending with distinct nodes, and is brownish yellow; the adventitious roots are yellowish white with wrinkled transverse stripes. The basal leaves are grayish green, broadly lanceolate, 40-60 cm long, 1.5-3 cm wide, gradually tapering at the tip, sheath-like at the base, light-colored, with a prominent midvein.
Stem robust, 60-70 cm tall, diameter 4-6 mm, with distinct longitudinal ridges, upper part branching, stem leaves shorter and narrower than basal leaves; bracts 3-4, membranous, green, lanceolate, 6.5-8.5 cm long, 1.5-2 cm wide, apex acuminate; flowers yellow, diameter 10-11 cm; peduncle 5-5.5 cm long; calyx tube 1.5 cm long, outer sepals ovate or obovate, about 7 cm long, 4.5-5 cm wide, claw narrow楔-shaped, centrally sunken into a groove, with black-brown stripes, inner sepals smaller, lanceolate, erect, 2.7 cm long, about 5 mm wide; stamens about 3 cm long, filaments yellowish white, anthers black-purple; style branches pale yellow, about 4.5 cm long, about 1.2 cm wide, apical lobes semicircular, margin with scattered teeth, ovary green, trigonal cylindrical, about 2.5 cm long, diameter about 5 mm.
Bloom period: May; fruiting period: June to August.