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..
[Physocarpa Raf. New Fl. N. A. 3: 73. 1836.] [Physocarpus Maxim. Acta Hort. Petrop. 6: 219. 1879.]
Branching shrubs, with petioled simple palmately lobed leaves, and white flowers in terminal corymbs. Calyx campanulate, 5-lobed. Petals 5, rounded, inserted in the throat of the calyx. Stamens 20-40, inserted with the petals. Pistils 1-5, short-stipitate, when 5 alternate with the calyx-lobes. Stigma terminal, capitate. Pods 1-5, inflated, in our species at length dehiscent along both sutures, 2-4-seeded. Seeds ovoid or globose, crustaceous, shining; endosperm copious. [Greek, resembling Opulus, the cranberry-tree.]
Species about 12, of North America, and 1 in Mantchuria. Type species: Spiraea opulifolia L.
Follicles glabrous, shining.
Spiraea opulifolia L. Sp. Pl. 489. 1753.
Neillia opulifolia Brew. & Wats. Bot. Cal. 1: 171.
1876. Opulaster opulifolius Kuntze, Rev. Gen. Pl. 949. 1891.
A shrub 3°-10° high, with recurved branches, glabrous twigs and foliage, the bark peeling off in thin strips. Stipules caducous; leaves peti-oled, ovate-orbicular, obtusely or acutely 3-lobed, cordate, truncate or broadly cuneate at the base, 1'-2' long, or larger on the young shoots, the lobes irregularly crenate-dentate; corymbs terminal, peduncled, nearly spherical, many-flowered, 1'-2' broad; pedicels slender, glabrous or slightly pubescent, 5"-8" long; flowers white or purplish; calyx glabrous or somewhat pubescent; follicles 3-5, glabrous, shining, 3"-5" long, obliquely subulate-tipped, twice as long as the calyx.
River-banks and in rocky places, Quebec to Georgia, Tennessee and Michigan. June.
O. intermedius Rydb. in Britton, Man. 492. 1901.
Physocarpus intermedius C. K. Schneider, Handb. Laubh. 1: 807. 1906.
P. missouriensis Daniels, Univ. Mo. Stud. Sci. 1: 291. 1907.
A shrub similar to O. opulifolius in aspect, foliage and inflorescence, the leaves mostly narrower, and narrowed at the base. Calyx densely stellate-pubescent; follicles 3 or 4, abruptly acuminate, 3 1/2"-4" long, permanently stellate-pubescent.