Potentilla sect. Rubricaules
in J. M. Coulter and A. Nelson, New Man. Bot. Rocky Mt., 255. 1909.
Perennials, tufted to ± matted, not stoloniferous; taproots not fleshy-thickened; vestiture of long, short, crisped, and/or cottony hairs, glands sparse to abundant, sometimes red. Stems decumbent to erect, not flagelliform, not rooting at nodes, lateral to persistent basal rosettes, (0.2–) 0.5–3 (–4) dm, lengths (1–) 1.5–4 (–6) times basal leaves. Leaves: basal not in ranks; cauline 0–3; primary leaves usually palmate to subpalmate, sometimes some (rarely all) ternate, 1–10 cm; petiole: long hairs soft to stiff, ± appressed to spreading, glands sparse to abundant, sometimes absent; leaflets 3–5 (–7) (usually more than 3 on at least some leaves), usually at tip, sometimes to distal 1/6 (–1/4) of leaf axis, usually ± overlapping, oblanceolate to obovate, oblong, or elliptic, margins slightly to strongly revolute, distal 2/3 to whole length evenly incised 1/2–3/4+ to midvein, teeth 2–8 per side, surfaces ± to strongly dissimilar, abaxial usually grayish white to white, sometimes gray, cottony (or cottony-crisped) hairs abundant to dense, adaxial green to gray, not glaucous, long hairs soft to stiff. Inflorescences 1–12 (–20) -flowered, ± cymose, congested to open, sometimes solitary flowers. Pedicels ± straight in fruit, 0.2–2 (–5) cm, proximal often much longer than distal. Flowers 5-merous; hypanthium 2.5–6 mm diam.; petals pale-yellow or yellow, usually ± obcordate, (2–) 3–7 mm, equal to or distinctly longer than sepals, apex usually ± retuse; stamens ca. 20; styles subapical, ± columnar to tapered, papillate-swollen in proximal 1/5–1/2, rarely to nearly whole length, 0.7–1.2 (–1.5 in P. paucijuga) mm. Achenes smooth to faintly rugose.
North America, Eurasia
Species 35–40 (8 in the flora).
Section Rubricaules is used here for independently propagating species that have at least some palmate to subpalmate basal leaves and styles less than 1.5 mm that are thickened and glandular-papillate basally. Such species purportedly originated as intersectional hybrids between ternate sect. Niveae and pinnate to subpalmate sect. Pensylvanicae (J. Soják 1986). The North American representatives of the section essentially coincide with Potentilla rubricaulis in the broadest sense. Although some early annotations and treatments by the authors (for example, R. Elven and S. G. Aiken 2007) reflect an inclusive P. rubricaulis, the current treatment recognizes several reasonably distinct species, based on characters and geographic ranges as presented here. These are only the best-defined elements, with further investigation needed to resolve poorly understood variants and transition zones, especially in western Canada. One additional segregated element, P. saximontana, is placed here in sect. Subjugae. Minor elements reported from North America but not otherwise addressed in the current treatment include P. borealis Soják, P. insularis Soják, P. murrayi Jurtzev, P. petrovskyi Soják, and P. psychrophila Soják.
The name Potentilla nivea var. pentaphylla Turczaninow (mistakenly attributed to Lehmann) and its replacement name P. quinquefolia Rydberg, although commonly used as a synonym of P. rubricaulis, do not apply to North American plants (B. Ertter et al. 2013). Independent of the name itself, references to P. quinquefolia from Oregon (C. L. Hitchcock and A. Cronquist 1961b) are based on specimens of P. gracilis var. owyheensis; the voucher for P. quinquefolia in Washington has been reidentified as P. argentea.
Potentilla nivea var. subquinata Lange [= P. subquinata (Lange) Rydberg, P. nivea subsp. subquinata (Lange) Hultén] is another name often used for members of this group. As discussed under sect. Niveae, however, the lectotype is here interpreted as the casual hybrid of P. arenosa and P. nivea. Plants of otherwise trifoliolate species in sect. Niveae will sometimes produce supernumerary leaflets; such plants might key to sect. Rubricaules and should be evaluated in a population context.
Further discussion and synonymy of all these species, and the section in general, are provided elsewhere (B. Ertter et al. 2013).
|1||Inflorescences congested or ± elongating in fruit; pedicels 0.2–0.7(–1) cm, proximal to 1.5 cm; basal leaves usually palmate or subpalmate, rarely ternate on same plant||> 2|
|1||Inflorescences ± open, sometimes solitary flowers; pedicels (0.5–)1–3 cm, proximal to 5 cm; basal leaves often both ternate and palmate or subpalmate on same plant||> 4|
|2||Leaves subpalmate, proximalmost leaflets separated by 1–5 mm; styles 1.2–1.5 mm; petals (4–)5–6 × 4.5–5.5 mm; hypanthia 3.5–5 mm diam.; La Sal Mountains, Utah.||Potentilla paucijuga|
|2||Leaves usually palmate, rarely subpalmate or ternate, proximalmost leaflets separated by 0–2 mm; styles 1–1.2 mm; petals 2–5 × 2–4 mm; hypanthia 3–4 mm diam.; Rocky Mountains to California||> 3|
|3||Petioles: long hairs weak to ± stiff, ± ascending to almost spreading, 1–2 mm; sepals: glands abundant, usually not obscured; leaflets incised 1/2–3/4 to midvein, teeth (1–)2–5 mm; Idaho and Montana to Utah and Colorado.||Potentilla modesta|
|3||Petioles: long hairs stiff, ± appressed, 0.5–1.2 mm; sepals: glands sparse, obscured; leaflets incised 3/4+ to midvein, teeth (2–)3–6(–10) mm; California.||Potentilla pseudosericea|
|4||Inflorescence branch angles 5–30(–50)°; petals 3–5(–6) × 3–4(–5) mm, slightly longer than sepals, not overlapping; ne British Columbia, Yukon, interior Alaska.||Potentilla furcata|
|4||Inflorescence branch angles (10–)20–50°; petals 3–7 × 4–8(–9) mm, usually distinctly longer than sepals, sometimes overlapping; Alaska to Greenland, s to Nevada and Colorado||> 5|
|5||Petioles: long hairs ± weak to stiff, 0.5–1.5(–2) mm; adaxial leaflet surfaces: long hairs usually stiff; leaflet teeth: apical tufts 0.5–1 mm; proximalmost leaflets separated by 0(–1) mm; mostly subarctic and alpine; w North America||> 6|
|5||Petioles: long hairs soft to ± stiff, 1–2.5 mm; adaxial leaflet surfaces: long hairs soft to ± weak; leaflet teeth: apical tufts 1–1.5 mm; proximalmost leaflets separated by 0–2 mm; arctic, n Canada, Greenland||> 7|
|6||Stems 1.5–4 dm; basal leaflet teeth (4–)5–8 per side; inflorescences 4–20-flowered; hypanthia 4–6 mm diam.; ± subarctic regions of nw Canada, Alaska.||Potentilla rubricaulis|
|6||Stems (0.3–)0.5–2 dm; basal leaflet teeth 2–6 per side; inflorescences 1–6(–8)-flowered; hypanthia 3–4 mm diam.; mostly alpine regions, Rocky Mountains to eastern Great Basin.||Potentilla hookeriana|
|7||Inflorescences (1–)3–7-flowered; petioles: long hairs 1–2 mm, weak to ± stiff, verrucose; leaflet teeth: apical tufts ± 1 mm; adaxial leaflet surfaces: short (short-crisped) hairs absent or sparse, rarely common, cottony hairs absent; caudex branches not sheathed with marcescent whole leaves; petals usually not overlapping.||Potentilla pedersenii|
|7||Inflorescences 1–3(–4)-flowered; petioles: long hairs (1–)1.5–2.5 mm, soft to ± weak, smooth; leaflet teeth: apical tufts 1–1.5 mm; adaxial leaflet surfaces: short/crisped/cottony hairs common to abundant; caudex branches often sheathed with marcescent whole leaves; petals often overlapping.||Potentilla uschakovii|
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