Silene hawaiiensis is a sprawling shrub with stems originating from an enlarged fusiform root, growing to a length of 15–40 cm. The stems are ascending to scandent and are viscid puberulent to puberulent, especially on the younger parts, often swollen at the nodes. The leaves are simple, either opposite or whorled, with slender, recurved, subulate blades that are 6–15 mm long and 0.5–0.8 mm wide. The leaf bases are often connate around the stem, and the surfaces are puberulent or viscid puberulent, especially along the margins and towards the base. The leaf margins are entire, and the leaves are sessile. Stipules are absent. The flowers are arranged in narrow, paniculate, or sometimes sub-racemose cymes with puberulent or viscid puberulent surfaces. The flowers are bisexual (perfect) and actinomorphic (radially symmetric), with 3–6 mm long pedicels. The calyx is usually purple or purple-tinged, 5-toothed, 11–14 mm long, faintly 10-nerved, puberulent, viscid, or sometimes glabrous, with acute, sparsely ciliate lobes and narrow, scarious, ciliate margins. The corolla consists of 5 greenish-white petals above and below, drying completely maroon, with blades 4.5–5.5 mm long, deeply cleft, and exserted 3–4 mm beyond the calyx. The base of the petals has a 2-lobed appendage that is exserted about 3 mm beyond the calyx. The stamens are included to barely exserted beyond the calyx. The ovary is superior, 1-celled or incompletely 2–4 celled, situated on a well-developed stipe (carpophore) that is adnate to the staminal filament bases and petal bases, measuring about 5 mm long and enlarging to 7–8 mm long in fruit. The fruit is an oblong-ovoid capsule that is 1-celled throughout and measures 6.5–8 mm long. It dehisces by six or rarely three apical teeth or valves. The seeds are pale brown, irregularly cuneate, 0.7–0.9 mm long, and papillose, with somewhat depressed faces. It is found in scattered, primarily open, dry areas on decomposed lava and ash between 900-1,300 – 3,050 meters.