This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol2", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
S. alba DuRoi, Harbk. Baumz. 2: 430. 1772.
S. salicifolia lanceolata T. & G. Fl. N. A. 1: 415. 1840.
A shrub up to 6° high, the twigs yellowish-brown, puberulent when young. Leaves petioled, narrowly oblanceolate to oblong, puberulent on the veins beneath, sharply and mostly finely serrate, acute at each end, 1'-2 1/2' long, 5"-8" wide; inflorescence narrowly paniculate, densely puberulent or tomentulose; petals white, suborbicular about 1" long; follicles glabrous.
Spiraea tomentosa L. Sp. Pl. 489. 1753.
Erect, shrubby, usually simple, the stems floccose-pubescent. Leaves short-petioled, ovate or oval, 1'-2' long, 6"-12" wide, unequally serrate, obtuse or acutish at the apex, narrowed or rounded at the base, glabrous and dark-green above, woolly-pubescent with whitish hairs beneath; stipules deciduous or none; flowers pink or purple, rarely white, about 2" broad, in dense terminal panicles; follicles pubescent.
A shrub, 1°-3° high, simple or little branched, nearly glabrous throughout. Leaves petioled, rather thick, oval, ovate or orbicular, narrowed, rounded or slightly cordate at the base, obtuse at the apex, unequally serrate with pointed teeth, especially above the middle, green above, paler and sometimes minutely pubescent beneath, 1 1/2-3' long, 1'-2' wide; stipules deciduous or none; flowers white, about 2" broad in dense compound terminal often leafy corymbs; follicles glabrous.
S. virginiana Britton, Bull. Torr. Club 17: 314. 1890. A much-branched shrub, the branches forming wands 1°-4° long, more or less pubescent when young, becoming glabrous. Stipules deciduous or none; leaves petioled, oblong or oblanceolate, thin, obtuse or acutish at the apex, cuneate or rounded at the base, 1 1/2'-2' long, 5"-8" wide, green above, pale or slightly glaucous beneath, entire, or with a few low teeth above the middle; petioles 1"-2 1/2" long; flowers white, about 3" wide, in terminal compound corymbs; petals ovate-orbicular; pedicels and calyx glaucous; follicles glabrous.
On damp rocks, West Virginia to the mountains of North Carolina and Tennessee. June.