Description from Flora of China
Carex macrocephala Willdenow ex Sprengel var. kobomugi (Ohwi) Miyabe & Kudô; C. macrocephala var. longibracteata Oliver.
Rhizome long creeping, clothed with dark brown fibrous remnants of old glumes. Culms 10-20 cm tall, 3-4 mm thick, erect, rigid, obtusely trigonous, subsmooth, clothed at base with dark brown sheaths disintegrating into parallel fibers. Leaves longer than culm, blades yellow-green, broadly linear, 3-8 mm wide, flat, ± curved, leathery, serrulate margined. Lowest involucral bracts narrowly leaflike. Plants dioecious, rarely monoecious; male inflorescence oblong, 4-5 × 1.2-1.3 cm; female inflorescence ovate to oblong, 4-6 × ca. 3 cm; spikes numerous, ovate, 10-15 mm. Female glumes yellow-green, ovate to narrowly ovate, 12-16 × 4-5 mm, leathery, many veined, margins broadly hyaline, broad costa excurrent into a long scabrous awn, apex acute, usually toothed. Utricles yellow-greenish, slightly shorter than or ± equaling glume, lanceolate or ovate-lanceolate, plano-convex, 10-15 × ca. 4 mm, leathery, lustrous, finely many veined on both faces, narrowly winged margins irregularly serrulate-scabrous on upper part, apex gradually tapering into a long weakly incurved beak, orifice 2-toothed. Nutlets olivaceous, loosely enveloped, oblong-obovate or oblong, compressed trigonous, base slightly cuneate, apex rounded; style sparsely pilose below, base slightly thickened; stigmas 2. Fl. and fr. Jun-Sep. 2n = 84.
Carex macrocephala Willdenow ex Sprengel has been attributed to China (see Fl. N. Amer. 23: 309. 2002); its range includes coastal areas of NW North America and NE Asia (Japan, Russia). However, we have found no specimens from China, and the reports probably can be traced to an older usage of C. macrocephala, which included C. kobomugi.
Seashores, riversides, sandy lakeshores. Anhui, Hebei, Heilongjiang, Jiangsu, Liaoning, Shandong, Taiwan, Zhejiang [Japan, Korea, Russia (Far East)].