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FNA | Family List | FNA Vol. 9 | Rosaceae | Potentilla

8u. Potentilla Linnaeus sect. Pensylvanicae Poeverlein in P. F. A. Ascherson et al., Syn. Mitteleur. Fl. 6(1): 669. 1904.
[(as Pennsylvanicae)]

Barbara Ertter, Reidar Elven

Potentilla [unranked] Multifidae Rydberg; Potentilla sect. Multifidae (Rydberg) A. Nelson; Potentilla ser. Multifidae (Rydberg) T. T. Yu & C. L. Li

Perennials, ± tufted, not stoloniferous; taproots not fleshy-thickened; vestiture of long, short, crisped, and/or cottony hairs, glands sparse to abundant, sometimes absent, not red. Stems decumbent to erect, not flagelliform, not rooting at nodes, lateral to persistent basal rosettes, (0.1–)0.5–4(–6) dm, lengths (1–)1.5–3(–4) times basal leaves. Leaves: basal not in ranks; cauline 1–4; primary leaves pinnate to subpinnate or subpalmate (with distal leaflets distinct), 1.5–25(–30) cm; petiole: long hairs spreading to appressed, soft to stiff, glands absent or sparse to abundant; leaflets (3–)5–13(–19), on distal 1/6–1/2+, rarely less, of leaf axis, separate to ± overlapping, narrowly oblanceolate or elliptic to obovate or broadly oblong, margins ± to strongly revolute, ± whole length evenly incised ± 1/2 to nearly completely to midvein, teeth (2–)3–8(–12) per side, surfaces similar to strongly dissimilar, abaxial green to white, cottony hairs absent or sparse to dense, adaxial green to grayish, not glaucous, long hairs soft to ± stiff. Inflorescences (1–)2–40(–100)-flowered, cymose, congested to very open. Pedicels ± straight in fruit, (0.1–)0.2–3(–5) cm, proximal often significantly longer than distal. Flowers 5-merous; hypanthium 2.5–10 mm diam.; petals pale to bright yellow, obovate to obcordate, (2–)3–5(–10.5) mm, +\- equal to or longer, sometimes shorter, than sepals, apex rounded or truncate to retuse; stamens (15–)20; styles subapical, conic to columnar, papillate-swollen in proximal 1/4–3/4+ or only at base, if at all, 0.8–1.2(–1.5) mm. Achenes smooth to rugose.

Species ca. 20 (8 in the flora): North America, ne Mexico, Eurasia, n Africa.

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).

SELECTED REFERENCE FloraAuthorKohli, B. L. and J. G. Packer. 1976. A contribution to the taxonomy of the Potentilla pensylvanica complex in North America. Canad. J. Bot. 54: 706–719.

1 Styles papillate-swollen at very base, if at all; inflorescences ± congested to very open   (2)
+ Styles papillate-swollen in proximal 1/4–3/4+; inflorescences usually congested, sometimes elongating in fruit (± open in P. pulchella)   (3)
2 (1) Sepal venation prominent at least proximally; inflorescences (5–)10–40+-flowered, ± congested to open; pedicels 0.3–1 cm (proximal to 3 cm).   97 Potentilla bimundorum
+ Sepal venation indistinct; inflorescences 2–5-flowered, very open; pedicels 2–4 cm.   98 Potentilla anachoretica
3 (1) Basal leaves pinnate, short hairs usually abundant to dense, rarely absent, sometimes obscured (especially in Great Plains); leaflets (2–)3–6(–9) per side, on distal (1/3–)1/2–3/5 of leaf axis; cottony and crisped hairs absent abaxially; epicalyx bractlets: lengths 1–2 times sepals, margins ± revolute   (4)
+ Basal leaves subpinnate to subpalmate, short hairs absent, sparse, or obscured; leaflets (1–)2–3 per side, on distal 1/6–1/3(–1/2) of leaf axis; cottony and/or crisped hairs absent or sparse to dense abaxially; epicalyx bractlets: lengths 1/2–1 times sepals, margins revolute or not   (5)
4 (3) Leaflets: teeth 4–8(–10) per side, margins incised ± 3/4 to midvein, leaving undivided medial blade 2–4(–8) mm wide; epicalyx bractlets equal to length of sepals; widespread.   91 Potentilla pensylvanica
+ Leaflets: teeth 8–12 per side, margins incised ± 1/2 to midvein, leaving undivided medial blade 5–9 mm wide; epicalyx bractlets 1–2 times length of sepals; sandy sites, n Great Plains.   92 Potentilla lasiodonta
5 (3) Inflorescences ± open, (1–)2–5(–9)-flowered; pedicels 0.5–5 cm; leaflet teeth 2–5 per side; Alaska, n Canada, Greenland.   96 Potentilla pulchella
+ Inflorescences congested, sometimes elongating in fruit, (1–)3–50(–100)-flowered; pedicels 0.2–1(–3) cm; leaflet teeth (2–)3–8 per side; Alaska to Newfoundland, s to California, Colorado, and New Hampshire   (6)
6 (5) Petals (4–)5–6 × 4.5–5.5 mm, longer than sepals; styles 1.2–1.5 mm; leaflets incised 2/3–3/4 to midvein; stems 0.5–2(–2.5) dm; La Sal Mountains, Utah.   88 Potentilla paucijuga (sect. Rubricaules) (in part)
+ Petals 2–5 × 2–4 mm, ± equal to sepals; styles 0.8–1.2(–1.5) mm; leaflets incised 3/4+ to midvein; stems (0.2–)0.5–5(–6) dm; widespread   (7)
7 (6) Sepals: glands absent, sparse, or obscured; leaflets usually white abaxially, cottony (and sometimes crisped) hairs ± dense.   95 Potentilla bipinnatifida
+ Sepals: glands abundant, evident at least distally; leaflets usually green to grayish abaxially, cottony hairs absent, crisped hairs absent or sparse to abundant   (8)
8 (7) Epicalyx bractlets: lengths 2/3–1 times sepals, margins ± revolute (at least in fruit); stems (0.4–)1–4.5(–6) dm; n Atlantic Coast and Hudson Bay across n prairies to n Rocky Mountains; 0–2200 m.   93 Potentilla litoralis
+ Epicalyx bractlets: lengths 1/2–3/4 times sepals, margins flat; stems (0.2–)0.5–2.6 dm; Great Basin and surrounding mountains; 2500–3700 m.   94 Potentilla jepsonii


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