Plants loosely cespitose; rhizome internodes 7-58 mm, 1.2-2.2 mm thick. Culms purple-red to 4.8-11.4 cm at base, 8.9-39 cm; vegetative shoots 33-59 cm, 1.4-2.2 times as tall as culms. Leaves: green, widest blades 3-4.6 mm wide. Inflorescences 8.1-29 cm, 0.73-0.95 of culm height; internode between proximalmost scales in proximalmost spike 2.4-3.5 mm; internode between distal lateral spikes 0.4-7.4(-9.8) cm, longest internode between distal lateral spikes 0.9-7.4(-9.8) cm; peduncle of terminal spike 0.3-3.2(-6.8) cm, longest peduncle per plant 0.87-3.2(-6.8) cm; proximal bract sheaths tight, hyaline band of adaxial face of sheath with apex truncate or concave; ligules 4-4.9(-9.6) mm; blades uniformly green, bract blade of distalmost lateral spike exceeding terminal spike, longest bract blade of distalmost lateral spike 3.2-9.5 cm. Spikes 4-6, distalmost 2-3 spikes overlapping or, rarely, all spikes separate; lateral spikes pistillate, with 2-12 perigynia, longest spike per plant with (5-)7-12, 7-20 × 3.5-4.8 mm, ratio of longest lateral spike length (in mm) to flower number = 1.8-2.5; terminal spike 14-38 × 1.2-2.1 mm, longest per plant 17-38 mm, exceeding distalmost lateral spike Pistillate scales 2.5-4.2 × 1.4-2.2 mm, body 1.5-2.4 mm, midrib prolonged as awn 0.4-2.4 mm. Staminate scales 3.9-4.8 × 1.2-1.8 mm, apex acute, awn 0-2.2 mm. Perigynia distichously imbricate, prominently 49-66-veined, slightly inflated, narrowly obovate in outline, obtusely trigonous in cross section, 4.1-4.7 × 1.4-1.6, 2.7-3.1 times as long as wide, 1.8-1.9 times as long as achene bodies, base gradually tapered, apex gradually tapered; beak absent or straight, 0-0.4 mm, 0-0.1 of perigynium length. Achenes 2.9-3.4 × 1.3-1.4 mm, tightly enveloped by perigynia, base abruptly contracted, apex abruptly contracted; stipe 0.5-0.6 mm; body 2.2-2.6 mm; beak straight, 0.1-0.3 mm.

Fruiting spring. Mesic deciduous forests, in sandy loams; of conservation concern; 0-30 m; Fla.

Carex paeninsulae is rare and restricted to the northern half of the Florida peninsula.