Luzula hawaiiensis var. oahuensis is a perennial herb with a firmly to weakly cespitose growth form. The stems are erect and can range up to 7 meters long, marked by an inconspicuous striation. The leaves are primarily basal, typically 1–2(3) per stem. The leaf blades are linear, measuring 5–30 cm long and 1–10 mm wide, terminating in a mucronate apex. The leaf margins are densely pubescent, especially when young, and tend to become glabrate as they mature. It lack both petioles and stipules. The flowers occur in (2)3–8(–10) flowers grouped in subglobose glomerules, each subtended by papery or scarious bracts. These flowers contribute to cymose, terminal inflorescences, occasionally accompanied by a smaller, lateral inflorescence emerging from the lower node within the axil of a single foliar bract. The bracts that subtend the inflorescence range from 1–4 are foliaceous and can be 2–10 cm long. Each flower is further subtended by 2–3(4) acuminate bracteoles with laciniate to subentire margins. The flowers are bisexual (perfect), featuring perianth parts that are pale yellowish brown to dark brown, linear, and subulate, with narrow hyaline margins. The outer perianth segments are 2.5–4.5 mm long, and the inner ones are 2–3.5 mm long. Six stamens with anthers are as long as or longer than the filaments. The pollen grains are notable for remaining in tetrads surrounded by a common exine. The ovary is superior, sessile, and 1-celled with basal placentation, hosting three anatropous ovules, and the styles are approximately as long as the ovary itself. The fruits are capsules that are pale brown to reddish brown, glossy, trigonous, and oblong or ovoid, typically shorter than the perianth. The seeds are red to dark brown, ellipsoid to ovoid, 1–1.5 mm long, with rugulose surfaces, often featuring a white micropylar caruncle and a conical protuberance at the apex. It is found in open or rocky sites, including slopes, cliffs, ridges, and open areas within mesic forests and shrublands. It is also found in subalpine forests, shrublands, and grasslands, between 730 – 2,560 meters.