Rhizome short, indurate. Culms loosely tufted, 15-30 cm tall, obtusely trigonous, smooth, stiff, with nodes, thickened to bulbous at base, clothed with dark brown sheaths disintegrating into fibers. Leaves longer than culm, blades narrowly linear, 2.5-3 mm wide, flattish plicate, rather stiff, slightly scabrous on margins, long sheathing. Lowest involucral bract leaflike, much surpassing inflorescence. Inflorescence long cylindric, 5-9.5 cm; spikes numerous, androgynous, ovate, 5-7 × 3-4 mm. Female glumes pale ferruginous, with brownish spots, ovate, 2.5-2.8 mm, margins white hyaline, green 3-veined costa forming a short mucro at acute apex. Utricles pale brown with dark spots, equaling or slightly longer than glume, ovate or ovate-elliptic, plano-convex, 2-2.5 × 1.8-2.5 mm, subleathery, narrowly winged, serrulate above, finely many veined abaxially, apex gradually narrowed into a beak ca. 0.3 mm, serrulate on upper margins, orifice 2-toothed. Nutlets brown, tightly enveloped, oblong-ovate, plano-convex, ca. 1.2 mm; stigmas 2. Fl. and fr. Apr-Aug.

A variant of this species (from Guizhou and Sichuan), with utricles broader and nerveless or weakly veined, was recognized in FRPS (12: 473. 2000) under the name "Carex thompsonii Franchet." However, Franchet’s name was not validly published and was apparently only an orthographic variant of Boott’s name. From the few specimens available, "C. thompsonii" cannot be reliably distinguished from C. thomsonii.

Sandy and wet places along rivers, grassland slopes; 200-1700 m. Guangxi, Guizhou, Sichuan, Yunnan [Bhutan, NE India, N Myanmar, Nepal, N Thailand, N Vietnam].