Flora of North America species comparison

Varieties 2 (2 in the flora).

Because of variation in the degree of hairiness on branches and leaves, thickness of leaves, leaf shape, sizes of racemes and flowers, and colors of fruits, Prunus virginiana has been split into forms, varieties, and segregate species. When viewed on a continental scale, most of the key characteristics used to separate these taxa intergrade enough so as to be useless.

The most useful distinction is between chokecherries found east of the Rocky Mountains and those found from the mountains westward. They differ in leaf shape and raceme size; the variation is imperfectly correlated. The eastern plants generally have their larger leaves obovate with lengths less than two times widths, racemes typically less than 7 cm, and petals to 4 mm. Plants of the Rockies and west have longer racemes and larger petals, and generally their larger leaves are elliptic to oblanceolate leaves with lengths two or more times widths. Distinctions between the eastern and western varieties are least obvious from Montana to eastern Washington north into British Columbia, where the varietal ranges overlap. Plants of the High Plains show intergradation between those of the Rockies and those of the East. The taxonomic solution provided here is a single species of chokecherry in North America with an eastern and a western variety that overlap in range along a line from northeastern New Mexico to southwestern British Columbia.

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

Traditionally treated as distinct species, Prunus alleghaniensis from the Appalachians and P. umbellata from southeastern United States are very similar; their ranges overlap in North Carolina and Tennessee. Similar plants disjunct in Michigan have been called P. alleghaniensis var. davisii. Morphological characters (petiole length, shape of blade along with its base and apex, degree of suckering) that have been used to separate these taxa vary as much within each taxon as among them. Since they can be separated only by geographic distribution, they are combined in this treatment.

Some specimens from Connecticut with hairy twigs, petioles, pedicels, and hypanthia were determined as Prunus alleghaniensis by Eames a century ago and do seem to fit within P. umbellata. Other Connecticut specimens determined as P. alleghaniensis (for example, Eames 121, MICH) with scattered glandular teeth on the sepals seem better placed in P. americana. The sole specimen known from Massachusetts (Pease 10,005, NEBC) has singly serrate leaves evenly tapered at both ends as in P. umbellata, but larger petals and reflexed sepals like those of P. americana.

In the southeastern United States, hairy forms have been called Prunus injucunda or P. mitis; the degree of indument on the twigs, petioles, leaf surfaces, pedicels, hypanthia, and sepals is subject to much trivial variation throughout the southeast, the Appalachians, and in Michigan.

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