Flora of North America species comparison

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.)

Species 7 or more (7 in the flora).

Section Graciles consists primarily of decumbent to erect, palmate-leaved, yellow-petaled perennials that are the most abundant Potentilla in mid-montane western North America. Most of the diversity treated here as five varieties of the most common species, P. gracilis, was divided by P. A. Rydberg (1908d) into 32 species arranged in six of his unranked groups: Candidae, Graciles, Longipedunculatae, Nuttallianae, Pectinisectae, and Permolles. The number of species in sect. Graciles as now defined is problematic. Although understanding of variation in the continental United States has benefited from the biosystematic analyses of J. Clausen et al. (1940), the potential Mexican representatives have not received equivalent attention. It is likely that some Mexican species placed by B. C. Johnston (1985) in sect. Ranunculoides (Th. Wolf) Juzepczuk are better accommodated in sect. Graciles, as already done here with an expanded circumscription of P. townsendii. Potentilla leptophylla Rydberg, the sole representative of group Heptaphyllae Rydberg, probably belongs in this section as well. The relationship of the North American sect. Graciles to the Eurasian sect. Chrysanthae remains to be determined.

The section contains some of the most taxonomically challenging groups among the North American cinquefoils, made all the more complex because its members often hybridize with species within and beyond sect. Graciles. Facultative apomixis is highly probable, resulting in populations of uncertain taxonomic status. The approach used here is to key and describe only the core representatives of the entities treated here, with some of the additional variation accounted for in the discussion.

The circumscriptions adopted here approximate those of J. Clausen et al. (1940), albeit with some species treated as varieties. Because the studies by Clausen et al. were centered in California, variation in the Rocky Mountains, Colorado Plateau, and northern prairies remains poorly analyzed.

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