Schiedea nuttallii is an erect to strongly ascending subshrub, typically reaching heights of 1–5 (–9) m. The stems are often swollen at the nodes, terete (cylindrical), 4-angled or -ridged, and many-branched. They are glabrous throughout except for the bracts and sepals, with purple-tinged internodes. The leaves are simple and opposite, with narrow ovate or lanceolate to narrow or broadly elliptic blades measuring 5–13 cm in length and 1.4–3.5 cm in width. The leaves are dull green, sometimes with purple tinges, slightly thickened and rubbery, becoming chartaceous when dry. Margins are entire and slightly thickened, becoming revolute toward the base. Petioles are weakly grooved and measure 0.3–1 cm long. Stipules are absent. The inflorescence is terminal, hosting 50–240 flowers on a 20–25 (–32) cm long structure. The pedicels are 6–12 mm long at anthesis, elongating to 10–20 mm in fruit, and are conspicuously asymmetrically flattened and weakly quadrangular. Flowers are bisexual (perfect). Sepals are 3.5–4.5 mm long, lanceolate, and green, sometimes purple-tinged. Stamens are dimorphic, with 10 in total. There are no petals. The ovary is superior and 1-celled. The capsules are narrowly ovoid, measuring 2.5–3.5 mm long. Seeds are approximately 1 mm long, orbicular-reniform, compressed. It is found in diverse mesic forests between 350–760 m.