Plants perennial. Culms 100–200 cm tall, 3–5 mm thick, smooth. Sheaths smooth or scabridulous, weakly keeled; ligules 1–1.5 mm, truncate; blades to 45 cm long, 6–10 mm wide, abaxial surfaces smooth or scabrous, adaxial surfaces scabrous. Panicles 20–30 cm long, 7.5–14 cm wide, open, pyramidal; branches 7.5–14 cm, spreading or reflexed, lax, with 16–80 spikelets; pedicels 2–7 mm. Spikelets 3.5–5.5 mm long, 2–3(3.5) mm wide, laterally compressed, oval in side view, with 3–5 florets. Glumes tapering from below midlength to the narrowly (< 45°) acute apices, veins not extending to the apices; lower glumes 0.8–1.5 mm; upper glumes 1.8–2.2 mm; rachilla internodes about 0.5 mm; lemmas 2.2–2.7 mm, 0.9–1.1 mm wide in dorsal view, veins distinctly raised, usually smooth over and between the veins, sometimes scabridulous over the veins, apices acute, prow-shaped; paleasslightly shorter than the lemmas, lengths 2–2.7 times widths, keels not winged, tips incurved, apices narrowly notched between the keels; anthers 2, about 1.5 mm, dehiscent at maturity. Caryopses about 1.5 mm. 2n = 40.
Glyceria nubigena is known only from moist areas of balds and high ridges in the Great Smoky Mountains of North Carolina and Tennessee.