Potentilla rivalis
Potentilla effusa
brook cinquefoil, brook or river cinquefoil, river cinquefoil, streambank cinquefoil
branch cinquefoil
decumbent to erect, sometimes prostrate, (0.5–)1–4(–7) dm, hairs at base not stiff, not tubercle-based, glands absent or sparse, inconspicuous.
(0.5–)1.5–4(–5.5) dm, lengths 2–3(–4) times basal leaves.
ternate, palmate, or subpalmate (with distal leaflets ± confluent), basal 3–15(–25) cm, cauline 2–7(–12) cm;
petiole: basal 1–9(–16) cm, cauline 0.5–4(–8) cm, long hairs usually common to abundant, ascending to spreading, 0.5–1.5 mm, usually ± weak, ± crisped hairs common to abundant, glands absent or sparse, inconspicuous;
leaflets 3–5(–7), at tip to distal 1/5 (basal) or 1/2 (cauline) of leaf axis, separate to ± overlapping, largest ones oblanceolate-elliptic to obovate, (0.5–)1–5(–6) × 0.5–2(–2.5) cm, distal 1/2–3/4 of margin evenly to unevenly incised 1/3–1/2 to midvein, sometimes cleft nearly to base, teeth 3–8 per side, surfaces moderately to abundantly hairy, glands absent or sparse.
pinnate, (3–)5–15(–25) cm;
petiole 0.5–5(–8) cm, long hairs absent to abundant, ± appressed, 1–3 mm, stiff to weak, short and crisped hairs absent or obscured, cottony hairs abundant (at least on first-formed leaves), glands sparse or obscured;
leaflets not conduplicate, lateral ones evenly to unevenly paired, 2–5(–7) per side (secondary leaflets sometimes interspersed) on distal 1/3–1/2 of leaf axis, distal pairs usually not decurrent or confluent with terminal leaflet, larger leaflets oblanceolate to narrowly obovate, 1–2.5(–3) × 0.3–1.3(–1.8) cm, distal (1/2–)2/3–3/4 (rarely more) of margin incised ± 1/2 to midvein, teeth (1–)2–9 per side, 1–4 mm, surfaces similar, gray to white or ± green, abaxial: long hairs sparse to common (at least on veins), 0.5–1.5 mm, weak to stiff, short or crisped hairs absent or sparse, sometimes obscured, cottony hairs absent or sparse to dense, glands absent, sparse, or obscured, adaxial: long hairs absent or sparse to common, short or crisped hairs absent or sparse, cottony hairs absent or sparse to abundant, glands absent or sparse.
2–6+.
(5–)20–100+-flowered.
7–30-flowered.
0.2–1(–2) cm.
0.3–3 cm.
epicalyx bractlets narrowly elliptic to ovate, (1.5–)2–4(–6) × 0.8–1.5 mm;
hypanthium (2–)3–5 mm diam.;
sepals 3–5 mm, apex broadly acute to obtuse;
petals pale yellow to yellow, broadly oblong-obovate, 1.5–2 × 1 mm;
stamens (5–)10(–15), filaments 0.4–0.9 mm, anthers 0.2–0.3 mm;
carpels 40–100, styles 0.5–0.6 mm.
epicalyx bractlets linear to narrowly lanceolate, 1–2.5(–3) × 0.3–1 mm, 1/2–2/3 as long as sepals, abaxial vestiture often much sparser than sepals, often glabrate or glabrescent distally, straight hairs absent or sparse, cottony hairs usually abundant (at least proximally), sometimes absent or nearly so (var. rupincola);
hypanthium 2–6 mm diam.;
sepals 3–6(–7) mm, apex long acuminate;
petals 4–6.5 × 4–6 mm;
filaments 1–3.5 mm, anthers 0.5–1 mm;
carpels 3–15, styles 1.5–2.1 mm.
yellowish, 0.7–0.9 mm, ± smooth, without a corky protuberance.
1.8–2.1 mm, smooth.
= 14, 70.
Potentilla rivalis
Potentilla effusa
Potentilla rivalis is most abundant in central and western North America; reports of occurrences in more eastern states (including those listed here) need confirming, as P. rivalis and P. norvegica often have been confused. Potentilla leucocarpa Rydberg was provided as a superfluous replacement name for P. millegrana; specimens annotated by Rydberg with this name include both P. biennis and P. rivalis.
Potentilla rivalis is sometimes divided into three species or varieties (for example, H. J. Scoggan 1978–1979). In a strict sense, var. rivalis has subpalmately compound (5-foliate) leaves. Variety milligrana, the most common phase, has 3-foliate leaves. Plants with both 3- and 5-foliolate leaves are var. pentandra, which also tends to have five stamens, though this latter character is not correlated with the leaf features. On the Great Plains, where var. pentandra is confined, all three expressions are often found in a single population (R. L. McGregor 1986b).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Varieties 2 (2 in the flora).
In the southern Rocky Mountains, Potentilla effusa is relatively distinct from P. hippiana both morphologically and geographically, with P. effusa mostly east of the Continental Divide and P. hippiana mostly west. In general, P. hippiana differs from P. effusa in having leaflets more evenly paired, more tightly serrate with teeth often occurring on the whole margin, and more bicolored with abaxial vestiture of crisped rather than cottony hairs. Stems of P. effusa have more cauline leaves on average than P. hippiana, and vestiture of epicalyx bractlets of P. effusa (as here circumscribed) is never sericeous.
The distinction between the two species is marred by intermediate populations throughout their shared range in the northern Rocky Mountains and Great Plains. Most regional floras focused on these areas have accordingly included Potentilla effusa within P. hippiana, sometimes without infraspecific distinction. An alternate solution has been the recognition of P. hippiana subsp. effusa, with the subspecies further subdivided into the two varieties recognized here. The varieties themselves intergrade; P. effusa var. ×coloradensis (Rydberg) Th. Wolf is available for the hybrid.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Leaflets gray to white, surfaces moderately long-hairy and moderately to densely cottony. | var. effusa |
1. Leaflets ± green, surfaces glabrous or sparsely to moderately long-hairy (at least on veins) and not or sparsely cottony. | var. rupincola |
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OR, 
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PNW Herbaria, Turner Photog. 
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