Geranium kauaiense is a decumbent (reclining) subshrub. Stems are reddish brown, often rooting at the nodes, growing embedded in moss mats or other bog plants, 49 to 100 cm long, with branches covered by persistent stipules (leaf-like appendages) and leafy only at the ends. The leaves are alternate, oblong to oblong cuneate (longer than broad, parallel-sided, sometimes tapering to a point at the base), 1.1 to 2.9 cm long, 0.4 to 0.8 cm wide, with the upper surface glabrous (hairless), the lower surface densely silky strigose (with stiff, flattened hairs), and margins entire (edges continuous) except four- to five-toothed at the apex. The flowers are usually three to four in terminal cymes that project beyond the leaves. The petals are white with purple veins, narrowly obovate (egg-shaped and attached at the narrow end), and 9 to 16 mm  long.  The fruit is septicidal and elastically dehiscent capsules separating into as many segments as carpels, a portion of the style splitting off from the remainder of the stylar column and forming an awn that recurves upward from the persistent central column, usually remaining attached to the apex; sometimes the awn also becomes spirally coiled; awn usually hygroscopic; immature carpel bodies ca. 2–7 mm long; densely pubescent. The seeds are ellipsoid; reticulate; ca. 2 mm long. It occurs in montane bogs and bog margins at 1,200-1,250 meters.