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.)

H. J. Scoggan (1978–1979, part 3) included Prunus emarginata within P. pensylvanica. Given that much of the problem of separating P. emarginata from P. pensylvanica arises from intermediate plants found in British Columbia and western Montana where the ranges of the two species meet, this makes some sense from a Canadian perspective. When viewed from a continental perspective, P. emarginata normally does not look much like P. pensylvanica (see notes on their differences under 10. P. pensylvanica).

Individuals of Prunus emarginata vary considerably in their habit, size and shape of leaves, and indument on branchlets, inflorescences, and leaves. Many segregate species have been described based on this variation. Most often, western botanists have recognized one species with two varieties based on habit or indument; those characters are not well correlated. Some keys use habit to separate the varieties (var. emarginata, a shrub, versus var. mollis, a tree, commonly used in Pacific Northwest floras); others have used indument (var. emarginata, glabrous, versus var. mollis, hairy, more commonly used in floras of the arid West). On the mountain slopes in the more arid portions of its range, P. emarginata is a thicket-forming shrub to about 6 m with the leaves expanding to no more than 50 mm; in the moister, milder climates of coastal Oregon to British Columbia, as well as the interior wetbelt of northern Idaho, northwestern Montana, and adjacent British Columbia, the plants are trees to 15 m with larger leaves expanding to 80 mm. Hairy plants occur throughout the range of P. emarginata, and glabrous plants are found from British Columbia to Arizona, generally not west of the Cascades.

Hybrids between Prunus emarginata and naturalized P. avium (P. ×pugetensis Jacobson & Zika) have been reported from the lowlands of western British Columbia, Oregon, and Washington.

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