Rock spiraea

Short-shoot leaf surfaces sessile- and/or stipitate-glandular, abaxial gray to off-white, veins, intercostal regions, and margins frequently obscured by hairs, tomentose to villous, often with white to gray granular deposits, adaxial puberulent, short-hirsute, velutinous to villous, sometimes hairs very short and surface appearing green to gray-green. Inflorescences 2–9 × 1–7 cm. Pedicels 2–3 mm. Flowers: nectar disc slightly pilose to puberulent, sometimes glabrous; sepals densely pilose to tomentose, usually eglandular; petal base abaxially with few, scattered long hairs.

Flowering Apr-–Aug. Rock outcrops, rocky sites in sagebrush and bitterbrush shrublands, edges of talus slopes; 500-–3100 m; Ariz., Calif., Colo., Idaho, Nev., Oreg., Utah, Wyo.; Mexico (Baja California).

Variety microphyllus has the widest range of the varieties. Individual populations are generally small and isolated.