Flora of North America species comparison

Prunus padus is cultivated in North America as an ornamental prized for its long, showy racemes of white flowers and its cold hardiness. Its value in the upper Midwest is often compromised by fungal infection causing black knot disease.

Prunus padus is difficult to distinguish from P. virginiana var. demissa, at least from herbarium material. Induments of hypanthium interior have been widely used in keys to separate the two: hairy in P. padus versus glabrous in P. virginiana. As noted by E. G. Voss (1972–1996, vol. 2), many of the specimens of P. virginiana have a pubescent hypanthium, especially basally. This is true throughout the range of P. virginiana, and also for some specimens of P. serotina. The hypanthia of P. padus are more hairy than those of P. virginiana. The petals of P. padus are longer than those of eastern chokecherry (P. virginiana var. virginiana), making it possible to distinguish flowering specimens from east of the Rocky Mountains. The petals are only slightly longer, on average, than those of P. virginiana var. demissa. Petals of P. padus are also a bit narrower and more elliptic. Shape of sepals may prove useful: 1.2–2 mm with lengths greater than widths in P. padus versus 0.7–1.4 mm with lengths equal to widths in P. virginiana var. demissa. In fruit, the difference between rugulose stones of P. padus and smooth stones of P. virginiana is subtle, perhaps too subtle for those unfamiliar with the range in variation of pit surfaces among these taxa.

(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.)