Description from Flora of China
Carex capituliformis Meinshausen ex Maximowicz; C. hakonensis Franchet & Savatier var. capituliformis (Meinshausen ex Maximowicz) Ohwi; C. hakonensis var. onoei (Franchet & Savatier) Ohwi; C. onoei subsp. capituliformis (Meinshausen ex Maximowicz) T. V. Egorova; C. onoei var. macrogyna Tang.
Rhizome short. Culms tufted, 20-40 cm tall, soft, slightly scabrid on angles, surrounded by pale brown basal leaf sheaths at base. Leaves shorter than culm, blades 1-1.5 mm wide, flat, soft. Inflorescence 1-spiked, terminal, androgynous, broadly ovate to spherical, 5-7 mm; male part not distinct, 2- or 3-flowered; most of spike female, usually 5- or 6-flowered. Female glumes pale brown laterally, broadly ovate, ca. 2 mm, membranous, pale on 3-veined costa. Utricles horizontally patent at maturity, ovate-oblong, obscurely trigonous, 2.5-3 mm, membranous, with distinct lateral veins especially abaxially, base subrounded, apex abruptly contracted into a short beak, orifice minutely 2-toothed. Nutlet tightly enclosed, obovate-oblong to elliptic, trigonous, ca. 2 mm; style base not thickened, persistent; stigmas 3.
Forests, wet grasslands, streambanks; 500-1600 m. Gansu, Hebei, Heilongjiang, Jilin, Liaoning, Shaanxi, Zhejiang [Japan, Korea, Russia (Far East)].