1a. Spiraea alba Du Roi var. alba
Spiraea ciliata Rafinesque; S. cuneifolia Borkhausen; S. lancifolia Hoffmannsegg; S. salicifolia Linnaeus var. lanceolata Torrey & A. Gray; S. salicifolia var. linearis Wenzig; S. salicifolia var. paniculata Aiton; S. tomentosa Linnaeus var. alba Marshall
Leaves: petiole 2–8 mm, puberulent; blade narrowly lanceolate to oblanceolate, 2–9 × 0.5–2.5 cm, length 3–4 times width, chartaceous, base cuneate, margins finely serrate to serrulate, apex acute. Panicles narrowly conic, 5–15 × 3–6 cm. Pedicels 1–2(–3) mm. Flowers 5–8 mm diam.; hypanthia abaxial surface usually puberulent to sparsely strigose, sometimes glabrous or glabrate; sepals 0.8–1 mm; petals 1.7–2 mm; stamens 40–50, 1 times petal length. 2n = 36.
Flowering Jun–Sep; fruiting Jun–Nov. Wetlands, fens, riparian areas, moist open sites; 0–300 m; Alta., Man., Ont., Que., Sask.; Ill., Ind., Iowa, Ky., Mass., Mich., Minn., Mo., N.Y., N.C., N.Dak., Ohio, Pa., S.Dak., Tenn., Vt., Va., W.Va., Wis.; introduced in Europe.
Variety alba is of conservation concern in Kentucky and Tennessee.