Flora of North America species comparison

Throughout most of its range, Prunus pensylvanica appears distinct from P. emarginata. The leaves of P. pensylvanica are generally larger and lanceolate to ovate-lanceolate rather than oblanceolate to elliptic; the leaf apices are usually acuminate (sometimes acute) versus rounded to obtuse (rarely acute) in P. emarginata. Inflorescences of P. pensylvanica are corymbose to umbellate with central axes shorter than pedicels; in P. emarginata the inflorescences are corymbose to racemose with central axes longer than pedicels. Where their ranges overlap in British Columbia and western Montana, intermediates are found with the corymbose inflorescence of P. emarginata and leaves more comfortably accommodated within the variation of P. pensylvanica. Some of these specimens have been identified as P. corymbulosa, based on a type from Montana, here included within P. pensylvanica.

Along the eastern slopes of the Rockies and throughout the northwestern Great Plains, Prunus pensylvanica is shrubby and has smaller leaves (less than 60 mm) than it does farther east. Compared to leaves of eastern plants, those of western specimens are also broader in proportion to their length (1.7–2.3:1 versus 2–4.3:1), have acute rather than acuminate apices, and tend to be more coarsely toothed. Although sometimes segregated as var. saximontana, or subsp. corymbulosa, when having a corymbose inflorescence, these plants fit within the variation in plant habit, leaf size, leaf shape, and margin serration seen throughout the broad range of P. pensylvanica.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

The name Prunus serrulata has been widely applied to P. speciosa by North American botanists and horticulturalists (for example, P. G. Russell 1934; A. J. Rehder 1940); some Japanese cherry experts now circumscribe P. serrulata more narrowly so that it includes only the white-petaled, double-flowered cultivars closely resembling the nomenclatural type. The single-flowered plants that are found escaping rarely and perhaps naturalizing in the flora area have been called P. lannesiana (Carrière) E. H. Wilson forma albida (Makino) E. H. Wilson or P. speciosa. Based on principal components analysis of 35 morphological characters from 468 individuals of the P. serrulata complex and related taxa, K. S. Chang et al. (2007) argued that forma albida is distinctive and separated from other taxa of the P. serrulata complex. H. Ohba (2001) recognized it at species rank as Cerasus speciosa (Koidzumi) H. Ohba. The classification and nomenclature of Japanese flowering cherries are complex, convoluted, and subject to varying interpretations, and no attempt is made to resolve them here. Centuries of selection and hybridization have blurred species distinctions, and it may be best to do as horticulturalists have and forsake botanical species names in favor of traditional and cultivar names. Whatever the name, these Japanese flowering cherries are widely grown as ornamentals where winters are not too cold nor summers too hot; they escape only rarely and have been found naturalizing only near planted specimens.

(Discussion copyrighted by Flora of North America; reprinted with permission.)