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.)

Potentilla bipinnatifida is similar to P. litoralis in habit and leaf dissection but has flat, silky epicalyx bractlets and sepals with no evident glands. Vestiture is generally silkier, and the silvery to bicolor leaves are white-cottony abaxially. The two species are sympatric in the plains of Canada, with some intergradation; P. bipinnatifida is also common south to Colorado, where it is found in intermontane meadows and sagebrush flats. Outlying populations occur in Blaine and Custer counties, Idaho, and Duchesne and Piute counties, Utah. Eastern collections from disturbed sites might be adventive.

Potentilla missourica Hornemann ex Lindley and P. normalis Besser ex Sprengel are older names for this species; both were rejected against a conserved P. bipinnatifida with designated lectotypes (see J. Soják 2008b).

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