Potentilla sect. Multijugae

Perennials, rosetted to ± matted, not stoloniferous; taproots often fleshy-thickened; vestiture primarily of straight hairs, not differentiated into long and short, crisped hairs often on stems and inflorescence, cottony hairs only in P. breweri, glands usually absent or sparse, rarely common, rarely ± red. Stems usually prostrate to decumbent, sometimes ascending (especially in supporting vegetation), not flagelliform, not rooting at nodes, lateral to persistent basal rosettes, (0.3–)0.5–5(–7) dm, lengths 1–3(–5) times basal leaves. Leaves: basal rarely ± 2-ranked; cauline (0–)1–3(–4); primary leaves pinnate (with distal leaflets distinct or confluent), (1.5–)2–20(–32) cm; petiole: long hairs soft to stiff, sometimes absent, spreading to ± appressed, glands usually absent or sparse; leaflets 7–21(–41), on distal (1/4–)1/3 to whole leaf axis, overlapping or not, oblanceolate to obovate, oblong, cuneate, flabellate, or elliptic, margins flat, distal (1/4–)1/2 to whole length evenly or unevenly incised ± 1/2 to completely to midvein, rarely entire, teeth (0–)1–5(–7) per side, surfaces ± similar, green to whitish, sometimes glaucous, long hairs, if present, soft to stiff, cottony hairs usually absent, sometimes sparse to dense (P. breweri). Inflorescences (1–)2–15(–25)-flowered, usually ± cymose, sometimes racemiform when prostrate, ± compact (P. arizonica) to very open. Pedicels recurved or straight in fruit, (0.5–)1–4(–6) cm, proximal often not much longer than distal. Flowers 5-merous; hypanthium 2–6 mm diam.; petals yellow, narrowly to broadly obcordate, (3.5–)4–10(–12) mm, equal to or longer than sepals, apex usually ± retuse; stamens (15–)20; styles subapical, filiform, often papillate-swollen in proximal 1/5 or less, (1.5–)2–3.5 mm. Achenes smooth to faintly rugose (± rugose in P. basaltica).

Distribution

w North America, c Mexico.

Discussion

Species 11 (10 in the flora).

Section Multijugae is used here for most North American species with fully pinnate leaves that have similar vestiture abaxially and adaxially, leaflets often so deeply divided and overlapping as to make the leaves nearly cylindric rather than planar, terminal leaflets often irregularly lobed and confluent with distalmost lateral leaflets, and relatively long styles somewhat glandular-papillate at the base. This circumscription includes the Mexican species Potentilla candicans Humboldt & Bonpland ex Nestler, which P. A. Rydberg (1898, 1908d) placed in its own group Candicantes.

This provisional circumscription of sect. Multijugae encompasses at least three species clusters. One cluster (species 40–45), largely coinciding with the original concept of group Multijugae Rydberg, tends to have fleshy-thickened taproots, prostrate stems that are usually no more than twice as long as the leaves, very open racemiform inflorescences with recurved pedicels, and carunculate achenes. This species cluster has evidently radiated in seasonally wet meadows in western North America, resulting in several highly localized endemics, two of which (P. multijuga, P. uliginosa) are presumed extinct (B. Ertter 1993; B. C. Johnston and Ertter 2010).

The second cluster consists of Potentilla breweri and P. versicolor, montane species with taproots that are not fleshy-thickened, stems usually more than twice as long as leaves, pedicels scarcely recurved in fruit, and no caruncle on the achenes. These differences from the previous species cluster are offset by the intermediacy of P. ovina.

Potentilla arizonica differs from both species clusters in its relatively congested and flat-topped inflorescences and anthers that are as long as or longer than the filaments. The species resembles the first species cluster in its fleshy-thickened taproots, but differs in that the stems are more likely to be decumbent to ascending, pedicels remain relatively straight in fruit, and achenes are not carunculate.

Since Potentilla drummondii (sect. Graciles), and P. macounii and P. morefieldii (sect. Concinnae) are sometimes identified as members of sect. Multijugae, they are included herein and key out in the third, tenth, and eleventh couplets, respectively.

Selected References

None.

Lower Taxa

Potentilla arizonica, Potentilla basaltica, Potentilla breweri, Potentilla hickmanii, Potentilla millefolia, Potentilla multijuga, Potentilla ovina, Potentilla plattensis, Potentilla uliginosa, Potentilla versicolor

Key

1	Largest leaflets: teeth 2–5(–7) on distal 1/4–1/2(–3/4) of margin, narrowly cuneate-oblanceolate to obovate, green, hairs absent (except on margins) or sparse	> 2
1	Largest leaflets: ultimate teeth or segments 2–10(–15) on distal 1/2 to whole margin, rarely 2(–3)-fid or entire, oblanceolate-cuneate or -oblong to flabellate, rarely elliptic (P. basaltica), green to white, hairs usually sparse to dense, sometimes absent or nearly so	> 3
2	Basal leaves 2–10(–13) cm; stem lengths (1.5–)2–3 times leaves; Rocky Mountains and e Great Basin.	Potentilla ovina
2	Basal leaves 10–22 cm; stem lengths 1–2 times leaves; coastal California.	Potentilla multijuga
3	Leaflets 2–4 per side on distal 1/10–1/2(–3/4) of leaf axis, incised ± 1/2 to midvein (often with additional incisions nearly to midvein), green on both surfaces.	Potentilla drummondii (sect. Graciles)
3	Leaflets usually more than 4 per side and/or on more than distal 1/5 of leaf axis, mostly incised more than 1/2 to midvein, green to grayish green or white on one or both surfaces	> 4
4	Largest leaflets (or at least distal ones in P. ovina) pinnately incised into linear to linear-oblanceolate teeth; distal leaflets ± distinct; Alberta to Arizona and e, barely entering British Columbia, Oregon, and Nevada	> 5
4	Largest leaflets usually ± palmately or unevenly (± evenly in P. multijuga) incised into linear to broadly elliptic or oblanceolate, sometimes ± ovate, teeth or segments, sometimes 2(–3)-fid or entire; distal leaflets ± confluent; California, Nevada, Oregon, Washington (or Alberta and Montana for P. macounii)	> 7
5	Anthers 1–1.5 mm, often as long as filaments; pedicels straight in fruit; leaflets on distal (1/2–)2/3–3/4 of leaf axis; Coconino County, Arizona.	Potentilla arizonica
5	Anthers 0.4–1 mm, usually ± 1/2 as long as filaments; pedicels usually ± recurved, sometimes straight, in fruit; leaflets on distal (1/4–)1/2–2/3(–3/4) of leaf axis; not Coconino County, Arizona	> 6
6	Leaflets: straight hairs 1–2 mm, loosely appressed, apical tufts on teeth 0.5–2 mm; fellfields, alpine ridges, rocky slopes, dry hillsides, 1500–3800 m.	Potentilla ovina
6	Leaflets: straight hairs ± 0.5 mm, tightly appressed, apical tufts on teeth less than 0.5 mm; moist meadows, streamsides, reservoir margins, 300–2900 m.	Potentilla plattensis
7	Primary lateral leaflets (5–)10–15(–20) per side on nearly whole leaf axis, entire or 2(–3)-fid to base (sometimes shallowly toothed as well), glaucous, straight hairs absent or sparse to common, 0.5 mm or less, tightly appressed; nw Nevada, ne California.	Potentilla basaltica
7	Primary lateral leaflets 3–10(–13) per side on distal 1/3–3/4(+) of leaf axis, incised 1/2 to completely to midvein into (1–)2–10(–15) ultimate teeth or segments, not glaucous, straight hairs sparse to abundant, sometimes nearly absent, 0.5–2 mm, ± appressed to spreading; California, Nevada, Oregon, Washington	> 8
8	Pedicels straight to slightly recurved in fruit; stem lengths 2–4(–5) times basal leaves; leaves green to white; achenes not carunculate; 1500–3600(–4000) m	> 9
8	Pedicels ± recurved in fruit; stem lengths 1–2 times basal leaves; leaves usually green, sometimes grayish green; achenes often carunculate; 0–2200 m	> 12
9	Leaflets: abaxial surfaces green to grayish green, cottony hairs absent, ultimate teeth or segments 2–5(–8); filaments (1–)1.5–2.5 mm; e Oregon, ne Nevada.	Potentilla versicolor
9	Leaflets: abaxial surfaces grayish green to white, cottony hairs sparse to dense, ultimate teeth or segments 3–10; filaments (1–)2–4 mm	> 10
10	Leaflets on distal 1/5–1/2 of leaf axis; Alberta, Montana.	Potentilla macounii (sect. Concinnae)
10	Leaflets on distal (1/4–)1/2–3/4+ of leaf axis; California, Nevada, Oregon, Washington	> 11
11	Leaflet surfaces ± similar, adaxial: cottony hairs sparse to dense, straight hairs soft; Sierra Nevada, Cascade Range, and n Great Basin.	Potentilla breweri
11	Leaflet surfaces ± to strongly dissimilar, adaxial: cottony hairs absent, straight hairs stiff; White Mountains and adjacent Sierra Nevada, California.	Potentilla morefieldii (sect. Concinnae)
12	Primary lateral leaflets incised 2/3 to completely to midvein, (3–)5–13 per side on distal 1/2–3/4+ of leaf axis, ultimate teeth or segments (0.5–)1–2.5 mm wide; California, Nevada, Oregon	> 13
12	Primary lateral leaflets incised 1/2–2/3(+) to midvein, 3–8 per side on distal 1/3–2/3 of leaf axis, ultimate teeth or segments (1–)1.5–3 mm wide; coastal California	> 14
13	Stems 0.4–2(–3) dm; basal leaves 2–15(–20) cm; leaflets on distal 2/3–3/4+ of leaf axis; interior California, Oregon, Nevada, 700–2200 m.	Potentilla millefolia
13	Stems 2.5–5.5 dm; basal leaves 15–32 cm; leaflets on distal ± 1/2 of leaf axis; Sonoma County, California, 30–40 m.	Potentilla uliginosa
14	Distal 1/2 to whole leaflet incised 1/2–2/3(+) to midvein; stems 0.5–2.5 dm; c California.	Potentilla hickmanii
14	Distal 1/3–2/3 of leaflet incised ± 1/2 to midvein; stems 2–5(–7) dm; s California.	Potentilla multijuga