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..
A shrub 2 1/2°-4 1/2° high, the twigs purplish-brown, finely villous when young. Leaves petioled, ovate to lanceolate, 4' long or less, 3/4'-1 1/2' wide, glabrous above, somewhat pubescent beneath, acute or acuminate at the apex, sharply serrate; inflorescence compound, corymbose, 2'-6' broad, finely villous; calyx turbinate, pubescent, its lobes triangular; petals pink or rose, obovate, 1 1/2" long; follicles glabrous.
Spiraea prunifdlia Sieb. & Zucc, a low shrub with lateral umbels of white, commonly double flowers 5"-6" broad, is much planted for ornament, and has escaped to roadsides in Connecticut and Massachusetts. It is native of Japan and China.
Spiraea chamaedrif˛lia L., also Asiatic, and much planted, has simple terminal corymbs of white flowers and small obovate leaves dentate above the middle. It has escaped to roadsides in New York.
Tall perennial herbs, with large 2-3-pinnate leaves, stipules minute or wanting, and very numerous white dioecious flowers in panicled spikes. Calyx mostly 5-lobed. Petals as many as the calyx-lobes. Stamens numerous, inserted on the calyx; filaments filiform. Pistils usually 3, alternate with the calyx-lobes. Follicles glabrous, at length reflexed, usually 2-seeded. Seeds minute, not shining. [Greek, goat's-beard.]
About 3 species, the following typical one widely distributed in the north temperate zone, one in northwestern America, the other Japanese.
Spiraea Aruncus L. Sp. Pl. 490. 1753.
Glabrous or pubescent; stem erect, somewhat branched, 3°-7° high. Leaves long-petioled, the lower 1° long or more, pinnate, 3-7-foliolate; leaflets ovate, lanceolate or oval, thin, stalked or sessile, acuminate or acute at the apex, rounded, slightly cordate or sometimes narrowed at the base, sharply doubly serrate or incised, 1'-3' long; spikes slender, elongated, erect or spreading; flowers 1"-2" wide; follicles short.
In rich woods, mountains of Pennsylvania to Iowa, south to Georgia and Missouri, and in northern Europe and Asia. Consists of several races, differing in pubescence and slightly in the size and shape of the fruit. Ascends to 4200 ft. in North Carolina. May-July.