Flora of North America species comparison

Species ca. 20 (8 in the flora).

Section Pensylvanicae, as here presented, accommodates most perennial species with pinnate to subpinnate leaves and styles ca. 1 mm that are frequently papillate-swollen proximally. Plants are often notably glandular, leaflet margins are usually revolute, and petals are most commonly about the same length as the sepals and often somewhat erect at anthesis. Section Multifidae was commonly used for this group of species until J. Soják (1987b) noted that sect. Pensylvanicae was an older, validly published name.

About half of the North American members of sect. Pensylvanicae have been previously included in a broadly defined Potentilla pensylvanica, with or without infraspecific divisions (for example, C. L. Hitchcock and A. Cronquist 1961b; S. L. Welsh 1974; R. L. McGregor 1986b; H. A. Gleason and Cronquist 1991). In support of a more narrowly circumscribed P. pensylvanica, B. L. Kohli and J. G. Packer (1976) found that major morphologic types coincide with three different ploidy levels. Most plants with fully pinnate leaves (five to nine leaflets in remote pairs) and other characters of typical P. pensylvanica in the narrow sense are tetraploid; plants with subpinnate leaves (mostly five leaflets in approximate pairs) are octoploid (or sometimes tetraploid; Packer, pers. comm.). Diploid populations from the northern Great Plains, morphologically closest to P. pensylvanica in the narrow sense but with epicalyx bractlets usually longer than the sepals, were named P. finitima Kohli & Packer (a later synonym of P. lasiodonta).

The ploidy differences noted by B. L. Kohli and J. G. Packer (1976), in combination with morphology (vestiture, glandularity, leaf dissection, and features of the epicalyx) and ecogeographic correlates, serve collectively to delimit the species that are recognized here. The most distinctive vestiture type is a velvety covering of short (0.2 mm), straight, spreading hairs that generally characterizes Potentilla lasiodonta and P. pensylvanica in the narrow sense, although this feature is sometimes obscured by longer ascending hairs or is missing altogether. Leaves of P. lasiodonta and P. pensylvanica in the narrow sense are also distinctly pinnate, with the blade comprising at least half the total leaf length and being no more than about half as wide as long, usually bearing at least three pairs of lateral leaflets gradually reduced in size from the distalmost, and the leaflets themselves being pinnately toothed with 4–12 blunt teeth per side. Epicalyx bractlets in both species, and also in P. litoralis, tend to be nearly as long as the sepals (to twice as long in P. lasiodonta) and concave, at least in fruit, with revolute margins and prominent midveins. These diagnostic features are not consistently present and/or evident, especially in depauperate and immature specimens, but collectively they serve to identify most specimens with a reasonable level of confidence. Occasional hybrids are to be expected.

In addition to the species addressed here, Potentilla lyngei Jurtzev & Soják subsp. lyngei has been reported from northeastern Greenland. At least one purported voucher (annotated by Jurtzev in ALA) has been reidentified to P. pedersenii (sect. Rubricaules), leaving the North American presence of P. lyngei subsp. lyngei in question. This is not the case for P. lyngei subsp. spissa Soják, described from Greenland; as discussed elsewhere (B. Ertter et al. 2013), this name is probably based on hybrids between P. pulchella and P. hyparctica (sect. Aureae), for which P. ×safronoviae Jurtzev & Soják is the priority name.

Additional nomenclatural details of species in sect. Pensylvanicae were provided by M. L. Fernald (1935), J. Soják (1987c), and B. Ertter (2008). For species of presumed hybrid origin with sect. Pensylvanicae as one parent, see sect. Rubricaules and Ertter et al. (2013).

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

Even in the reduced circumscription used here, Potentilla pensylvanica is exceptionally widespread, occurring in North America from Alaska to Hudson Bay, in the Great Plains and the North American Cordillera to northern Mexico. The species also grows across Siberia (where it has sometimes been called P. sibirica) and as isolated occurrences in the southwestern Alps and Spain (J. Soják 1987c; A. Kurtto et al. in J. Jalas et al. 1972+, vol. 13). One place P. pensylvanica does not occur is in Pennsylvania; the epithet was applied by Linnaeus to cultivated plants originating from Canada. Collections from Quebec are probably introductions (J. Cayouette, pers. comm.). The Oregon citation of P. pensylvanica (D. Mansfield 2000) refers to P. jepsonii.

Significant variation occurs within Potentilla pensylvanica, especially regarding vestiture and plant stature. J. Soják (1987c) has described several varieties, all Eurasian except var. brevipila (long hairs 0.6–1 mm); diminutive specimens from the Brooks Range of northern Alaska, isolated from other known populations of P. pensylvanica, have been described as P. brooksensis. Although much of the ecogeographic variation may merit recognition, at least at varietal level, doing so is postponed pending further analysis and clarification of nomenclature. Among the extremes are plants from the Great Plains, which have abundant long silky hairs overlying and obscuring the velvety layer of short hairs (resembling sympatric P. litoralis), and glabrate (except for glands) populations in Alaska. E. Hultén (1968) erroneously referred to the latter as P. pensylvanica var. glabrata (Lehmann) S. Watson; that name is a synonym of P. ovina var. ovina (sect. Multijugae). Most populations in Alaska also have larger than average flowers (petals to 7 × 7 mm, anthers ca. 1 mm).

Although Potentilla pensylvanica var. strigosa Pursh has been one of the most commonly used varieties in North America, the name has been effectively lectotypified by J. Soják (1987c) on a collection from Siberia. Soják identified this collection as the hybrid between P. pensylvanica and the Asian P. sanguisorba D. F. K. Schlechtendal; var. strigosa accordingly does not occur in North America.

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