Stems branched proximal to middle, slender. Leaves largest along middle of stems; petiole distinct, 1-6 mm; blade 3-20 mm. Pedicels filiform. Flowers: sepals erect, triangular, apex acute; petals elliptic to obovate, 3-6 mm, much longer than sepals. Capsules 2-5 mm. 2n = 16.

Flowering spring-summer. Wet, shaded cliffs and ledges, sometimes coastal or near waterfalls, mossy mats, wet rocks, moist crevices; 0-1200 m; Calif., Oreg., Wash.

Cascadia nuttallii is found from the coastal mountains to the western slopes of the Cascade Range, from extreme northwestern California to southwestern Washington. The accepted species name was validated in a correction slip attached to reprints of Johnson´s article describing Cascadia.