Plants perennial; cespitose, not mat-forming. Culms 3–16 cm, erect. Ligules 0.5–1.7 mm, acute, obtuse, or truncate, entire; blades usually involute and 0.4–0.7 mm in diameter, occasionally flat and 0.5–1.5 mm wide. Panicles 1.6–5.5 cm, usually contracted, sometimes diffuse, lower branches erect or ascending, spikelets usually confined to the distal 1/2; pedicels smooth, with tumid epidermal cells. Spikelets 3.5–7 mm, with 3–6 florets. Glumes slightly keeled over the back, veins distinct, apices acuminate to acute; lower glumes 0.7–1.3 mm; upper glumes 1.3–1.8 mm; calluses glabrous or with 5 or fewer hairs shorter than 0.1 mm; lemmas2–2.5 mm, herbaceous, usually purple with whitish margins, smooth, glabrous or with a few hairs on the bases of the lateral veins, backs rounded, 5-veined, veins distinct, not extending to the margins, apical margins smooth, apices obtuse to truncate, entire or slightly erose; palea veins smooth, glabrous; anthers0.6–0.9 mm. 2n = 14.
Puccinellia tenella is a halophytic, circumpolar subarctic and low arctic species. It is found above the high tide zone on sandy spits, in salt marshes, in silty soils, and among granitic rocks to 30 m above sea level. The above description applies to P. tenella subsp. langeana (Berlin) Tzevlev, the only subspecies in the Floraregion. Puccinellia alaskana Scribn. & Merr., considered a subspecies of P. langeana (Berlin) T.J. Sørensen ex Hultén [= P. tenella] by Sørensen (1953), has acute lemmas and hairs on the palea. It is discussed under P. pumila.