Poa sandvicensis is a cespitose perennial grass. The stems grow from short rhizomes that form a hardened culm base. The culms are erect to slightly decumbent, reaching 3–10 dm tall. They are slightly laterally compressed, glabrous to slightly retrorsely scabrous, and solid. Nodes are numerous, slightly swollen, and glabrous, while the internodes are relatively short, measuring 2.5–6 cm. The leaves are simple and alternate, with blades measuring 10–20 cm long and up to 6 mm wide. The upper surfaces are scabrous, while the lower surfaces are glabrous. The veins are parallel. The sheaths are striate and keeled, retrorsely scabrous toward the base, and glabrous toward the apex. They are closed to the mouth or split with age. The ligule is membranous, short, dentate, and less than 1 mm long, completely encircling the culm, with a hard tooth continuous with the ligule. Stipules are absent. The flowers are arranged in ovoid panicles, 3–5(–15) cm long, with few nodes. The branches are whorled, slender, and spreading to widely reflexed, with the lower branches extending up to 10 cm long. The spikelets (pictured) arise on the distal third of the branches, measuring 8–13-flowered and 10–15 mm long. They are long-pedicellate, compressed, and usually densely scabrous. The rachilla disarticulates between the florets and is elongated, with florets spaced up to 0.5 mm apart. The glumes are narrow, linear to lanceolate, 2.5–4 mm long, and 3-nerved, with scabrous nerves and an acuminate apex. Lemmas measure 4–5 mm long, are 5-nerved, and have a sparse tuft of cobwebby hairs at the base, particularly on the lower florets. The keel is scabrous, the lower part of the lateral nerves is also scabrous, while the intermediate nerves are faint. The margins are hyaline. Paleas are nearly as long as the lemmas, 2-nerved, with two scabrous-ciliate keels and an acute and bifid apex. The fruit is a golden brown to reddish brown caryopsis, obovoid, and about 0.5 mm long. It is found in wet and diverse mesic forests, particularly on shaded slopes, wet ridges, and ledges between 1,060-1,220 meters.