Flora of North America species comparison

Potentilla rivalis is most abundant in central and western North America; reports of occurrences in more eastern states (including those listed here) need confirming, as P. rivalis and P. norvegica often have been confused. Potentilla leucocarpa Rydberg was provided as a superfluous replacement name for P. millegrana; specimens annotated by Rydberg with this name include both P. biennis and P. rivalis.

Potentilla rivalis is sometimes divided into three species or varieties (for example, H. J. Scoggan 1978–1979). In a strict sense, var. rivalis has subpalmately compound (5-foliate) leaves. Variety milligrana, the most common phase, has 3-foliate leaves. Plants with both 3- and 5-foliolate leaves are var. pentandra, which also tends to have five stamens, though this latter character is not correlated with the leaf features. On the Great Plains, where var. pentandra is confined, all three expressions are often found in a single population (R. L. McGregor 1986b).

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

Potentilla pulcherrima is here retained provisionally in the broad sense, encompassing intergrades between morphological extremes. The most distinctive extreme has strictly palmate leaves and conspicuous red-tipped glands. Eglandular hairs are relatively sparse and spreading on epicalyx bractlets and abaxial leaflet veins, such that the veins tend to contrast with the cottony white abaxial surface. At the other extreme are plants with subpalmate leaves, no or inconspicuous glands, and densely strigose abaxial leaflet veins. The former is understood to be the core species, towards which the description is accordingly weighted. The latter in turn represents introgression with P. hippiana (sect. Leucophyllae) or other species. The subpalmate extreme includes the lectotype of P. pulcherrima (designated by J. Soják 1996), so if a narrower circumscription of the species is adopted then either P. filipes would become the accepted name of the core species or predominant current usage of P. pulcherrima would have to be conserved by designating a different type.

By whatever circumscription, Potentilla pulcherrima is one of the more common members of sect. Graciles in the Rocky Mountains, extending east into the northern prairies. The species grows mainly in the mountains from southeastern British Columbia and southern Alberta to northern and eastern Arizona and southern New Mexico. The native range extends at least to Manitoba and North Dakota, with outlying populations in the Black Hills of South Dakota. Populations are also scattered in the mountains of eastern Nevada and disjunctly in the White Mountains of California. Adventive occurrences in fields and disturbed sites are reported from as far east as Connecticut; see discussion of P. gracilis for reports from New Hampshire. All known specimens from Minnesota and Oregon have been reidentified as particularly hairy variants of P. gracilis in the broad sense; reports from Washington are suspect.

Potentilla pulcherrima has often been treated as a variety of P. gracilis, sometimes with the filipes extreme included in var. gracilis (B. Boivin 1967–1979). The current decision to treat P. pulcherrima as a species is in part because it has a monsoonal Rocky Mountain rather than a Pacific Northwest center of distribution.

Plants combining the vestiture of Potentilla pulcherrima, including abundant glandularity, with subpalmate leaves approaching P. hippiana (leaflets on about one-fifth of leaf axis) have been named P. gracilis var. hippianoides S. L. Welsh & N. D. Atwood.

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