Spiraea millefolium Torrey in War Department [U.S.], Pacif. Railr. Rep. 4(5): 83, plate 5. 1857

Stems: internodes (1–)6–12 mm. Leaves: stipules 2–4 mm, green on leaf base margins; blade 2.6–7(–9.6) × 0.9–2(–3) cm, 1(–2)-pinnate-pinnatifid into 13–25 pairs of pinnae; pinnae oblong-lanceolate, (4–)6–14(–16) × 2–4 mm, divided into 6–10 opposite or alternate pairs of obovate to ovate segments 0.8–2 mm; segments obtuse-rounded, entire or secondarily lobed on proximal margins, proximal margins decurrent along rachillae extending to subtending divisions (pinnae then pinnatifid and leaves then 2-pinnate), pinnae margins of proximalmost lobes decurrent along adaxial leaf rachises, abaxial surfaces of rachises, rachillae, and petioles hairy, adaxial glabrous. Inflorescences 3–15(–23) × 2–8(–12) cm, leafy proximally, flowers crowded along distal branches; lobes of distal bracts and bracteoles acute. Flowers: sepals valvate, 2.5–4 mm, acute, abaxial surface hairy, glandular; petals spreading, margins erose, glabrous; filaments spreading, inner more erect, 3–4 mm, glabrous, anthers orbicular, introrse, versatile, 0.4–0.5 mm; styles 3–5 mm. Follicles reddish brown, leathery, hairy. Seeds yellowish, 2.5–3.5 mm. 2n = 18.

Flowering Jul–Sep. Dry, rocky sagebrush scrub, pinyon-juniper woodlands, montane coniferous forests to subalpine woodlands; 900–3400 m; Ariz., Calif., Idaho, Nev., Oreg., Utah.

Chamaebatiaria millefolium grows in southern Oregon, northern California, and the eastern slope of the Sierra Nevada to southern Idaho, Nevada, north-central Arizona, and western Utah.