Shrub to 2 m tall Leaves: alternate, short-stalked, 3 - 7 cm long, narrowly oblong to narrow and inversely egg-shaped with a pointed tip, toothed, hairless or with few hairs along veins. Flowers: borne terminally in a pyramidal inflorescence (panicle-like) that is longer than wide, white (rarely pinkish), 4 - 7 mm across, with five spreading sepals, five petals and white stamens that are longer than the petals. Fruit: firm and dry, breaking open along one side (follicle), hairless, with tiny oblong seeds. Twigs: reddish brown, lightly hairly when young.
Similar species: Spiraea x billiardii differs by having a hairy lower leaf surface. Spiraea prunifolia has an unbranched inflorescence (umbel). Spiraea tomentosa has a densely hairy lower leaf surface, reflexed sepals, and hairy fruit.
Flowering: mid June to mid September
Habitat and ecology: Frequent in marshy meadows and along ditches, often in wet peaty or boggy soils.
Occurence in the Chicago region: native
Etymology: Spiraea comes from the Greek word speiraira, a plant used to make garlands. Alba means white.
Shrub to 2 m; lvs 3-7 cm, mostly broadest above the middle toothed, glabrous or nearly so; infl terminal, compound, paniculiform; fls white, seldom pinkish, 4-7 mm wide; sep spreading; fr glabrous; 2n=36. Nf. and Que. to Alta., s. to N.C., Mo., and S.D. June- Aug. Two copiously intergrading vars., widely overlapping geographically as well as morphologically:
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
From Flora of the Indiana Dunes (1930) - Donald C. Peattie
(Meadow-sweet) 3-12 dm. tall, with tough yellowish-brown stems; leaves lance-oblong, 5-7 cm. long, firm, finely serrate; inflorescence tomentose, in the form of a thyrse; flowers numerous, white, 6-8 mm. across. (S. salicifolia of auths., not L.) — Common in wet, boggy or peaty soil, and sandy low prairies, throughout. July, August.