Plants not cespitose. Culms straight, 25-60 cm. Leaves of flowering stems shorter than stem, to 13.5 cm × 1.5-3.1(-4.3) mm. Inflorescences: peduncles of staminate spikes 5-70 mm; bracts 90 × 0.7-2.2 mm; inner band of sheaths with brown, convex projection to 3.2 mm. Spikes: proximal pistillate spikes 1-3(-4), distant, erect or ascending, usually conspicuously pedunculate, ovoid to short-cylindric, proximal 10-20 × 5-9.5 mm; terminal staminate spikes 10-33 × 1.6-4.2 mm. Scales: pistillate scales dark brown, 2.1-3.9 × 1.4-2.4 mm, margins conspicuously white-hyaline; staminate scales with broad, white, hyaline margins. Anthers 2-3.6 mm. Perigynia ascending, yellowish, 3.1-5.5 × 1.2-2.1 mm, apex gradually narrowed into straight, serrulate beak; beak 0.7-1.6 mm. Achenes 1.5-2 × 1-1.5 mm.

Fruiting Jul-Aug. Moist to wet, open fens and meadows, on lime-rich soils; 0-500 m; St. Pierre and Miquelon; Nfld. and Labr., Que.; Mass.; Europe.

Carex hostiana was last collected in Massachusetts prior to 1836.