Potentilla plattensis
Potentilla ambigens
Platte cinquefoil, Platte River cinquefoil
silkyleaf cinquefoil, silkyleaf or giant or southern Rocky Mountain cinquefoil
initially decumbent to sometimes ascending, becoming prostrate or supported by vegetation, (0.3–)0.5–3.5(–4.5) dm, lengths 1.5–2.5(–4) times basal leaves.
(2–)3–7(–8) dm, lengths (1–)1.5–2.5 times basal leaves.
pinnate with distal leaflets ± distinct, 2–15(–20) × 1–3 cm;
petiole 0.5–5 cm, straight hairs common, tightly appressed, 0.5(–1) mm, stiff, cottony hairs absent, glands absent or sparse;
primary lateral leaflets (3–)4–6(–8) per side, on distal (1/4–)1/2–3/4 of leaf axis, overlapping to separate, largest ones obovate, 0.5–1.5(–2) × 0.5–1(–1.3) cm, distal (1/2–)2/3 to whole margin pinnately incised 3/4+ to midvein, ultimate teeth 5–10, linear-oblanceolate, 1.5–8(–10) × 1–2 mm, apical tufts less than 0.5 mm, surfaces green to grayish green, not glaucous, straight hairs sparse to common (sparser adaxially), tightly appressed, 0.5 mm, stiff, cottony hairs absent, glands absent or inconspicuous.
pinnate, 15–45(–50) cm;
petiole (5–)8–20 cm, long hairs abundant to dense, ascending to appressed, (1–)2–3 mm, ± stiff, rarely weak, short or crisped hairs absent or sparse, cottony hairs absent, glands sparse, often obscured;
leaflets not conduplicate, lateral ones evenly paired, (3–)4–7 per side on distal ± 1/2 of leaf axis, most pairs ± decurrent, rachis winged, distal sometimes confluent with terminal leaflet, larger leaflets narrowly obovate, (2–)3–7 × 1–2.5 cm, distal 3/4+ of margin incised 1/3 to midvein, teeth 6–18 per side, 1–4 mm, surfaces ± similar, abaxial grayish, long hairs sparse to common (mostly on veins), 0.5–2 mm, ± stiff, rarely weak, short-crisped hairs absent or sparse to common, cottony hairs absent, glands sparse to common, adaxial green to grayish, long and short hairs not differentiated, sparse to common, crisped and cottony hairs absent, glands absent or sparse.
1–3.
(0–)1–3.
(1–)3–15(–20)-flowered, loosely cymose, sometimes racemiform.
(10–)20–60-flowered.
1–4(–5) cm, ± recurved in fruit.
(0.5–)1–3(–6) cm.
epicalyx bractlets narrowly elliptic to linear-lanceolate, 2–5(–6) × 0.5–2 mm;
hypanthium 3–4 mm diam.;
sepals 3–6 mm, apex acute;
petals 4–7 × 3–6 mm;
filaments 1–2.5 mm, anthers 0.5–1 mm, usually ± 1/2 as long as filaments;
carpels 10–20, styles 1.5–2.5 mm.
epicalyx bractlets lanceolate to narrowly ovate or elliptic, 3–6 × 1–1.5 mm, 2/3 as long as to nearly equal to sepals, abaxial vestiture ± similar to sepals, not glabrescent, straight hairs sparse to common, crisped or cottony hairs usually absent;
hypanthium 3–6 mm diam.;
sepals 4–7 mm, apex acute to acuminate;
petals (6–)7–10 × 5–9 mm;
filaments (1–)1.5–4 mm, anthers 0.7–0.9(–1) mm;
carpels 20–30, styles (1–)1.8–3 mm.
(1.3–)1.5–1.9 mm, smooth, often ± carunculate.
1.4–1.6 mm, smooth.
= 70.
= 82.
Potentilla plattensis
Potentilla ambigens
Potentilla plattensis occurs mostly east of the Continental Divide from the Canadian Prairies to the mountains of New Mexico. The species barely enters Idaho at Monida Pass (Clark County). Populations also exist in the White Mountains of east-central Arizona and the mountains of southern Utah. The species is relatively uniform throughout its range but there is often significant seasonal variation, such that plants can be compact and densely strigose in early summer but elongate and subglabrous later in the season.
Where the ranges of Potentilla plattensis and P. ovina overlap, the two are sometimes difficult to distinguish. The habitats are usually distinct, in that P. plattensis generally occurs in moist valley bottoms and P. ovina occurs in rocky uplands. Differences in vestiture are also diagnostic: hairs of P. plattensis are 0.5 mm and tightly appressed; those of P. ovina are longer and looser.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Of conservation concern.
Potentilla ambigens is one of the more distinctive species in sect. Leucophyllae, comprising exceptionally large plants with large, coarsely hairy leaves. Although sometimes confused with P. hippiana, P. ambigens lacks the crisped-cottony vestiture of that species and is usually morphologically distinctive even where both species occur together (D. G. Anderson, www.fs.fed.us/r2/projects/scp/assessments/potentillaambigens.pdf).
Potentilla ambigens occurs in Wyoming (at least historically), along the eastern slope of the Rocky Mountains to northern Colorado, and in scattered locations in the high mountains of New Mexico as far south as the Sacramento Mountains, Otero County. The species is of conservation concern in Colorado and has not been documented in Wyoming since 1900 (D. G. Anderson, www.fs.fed.us/r2/projects/scp/assessments/potentillaambigens.pdf).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
OR
Flora NW
PNW Herbaria
SW CO Wildflowers
WildflowerSearch
iNaturalist
USDA Plants Database
