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..
Shrubs, with alternate simple pinnate or pinnatifid mainly stipulate leaves. Flowers terminal or axillary, racemose, cymose, corymbose or paniculate, white or pink, perfect. Calyx persistent, its tube mainly campanulate, 4-5-lobed. Petals 4-5, inserted on the calyx, short-clawed. Stamens 20-60, distinct, inserted on the calyx; filaments filiform; anthers didymous. Disk adnate to the calyx-tube. Pistils commonly 5 (rarely 1-8), superior, sessile or short-stipitate, alternate with the calxy-lobes. Stigmas capitate or discoid; ovules 2-00. Follicles usually 5, not inflated, dehiscent along 1 suture. Seeds linear, pendulous, the testa dull; endosperm none. [Greek, twisting, the pods twisted in some species.]
About 70 species, natives of the north temperate zone. Besides the following, about 12 others occur in the southern and western parts of North America. Type species: Spiraea salicifolia L.
Flowers in dense terminal panicles.
Glabrous or puberulent.
Leaves broadly obovate; inflorescence glabrous or nearly so.
Leaves narrowly oblanceolate or oblong; inflorescence densely puberulent or tomentulose.
Flowers in terminal corymbs.
Calyx glabrous; native.
Leaves broadly oval or ovate, thick, serrate.
Leaves oblong, thin, nearly entire.
Calyx pubescent; introduced.
An erect shrub, 2°-6° high, simple, or branched above, nearly glabrous, the stems reddish or purplish. Leaves petioled, broadly oblanceolate or obovate, glabrous or very nearly so, sharply and rather coarsely serrate, especially above the middle, 1'-2' long, 4"-18" wide, or on young shoots much larger, obtuse or acutish at the apex, cuneate to rounded at the base, pale beneath; stipules deciduous or none; flowers white or pinkish-tinged, 2"-3" broad, in dense terminal panicles; follicles glabrous.
Included in our first edition in the description of the Asiatic S. salicifolia L., which has pubescent inflorescence, pink flowers and narrower oblong leaves; it is sometimes cultivated and has escaped to roadsides in northern New York.