Potentilla plattensis
Potentilla arenosa
Platte cinquefoil, Platte River cinquefoil
thick, not columnar, not sheathed with marcescent whole leaves.
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.
ascending to erect, (0.3–)0.8–2.5(–4.5) dm, lengths (2–)3–5 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.
1.5–12(–20) cm;
petiole 1–7(–15) cm, long hairs sparse to abundant, spreading to ± ascending, rarely loosely appressed, 1–2(–2.5) mm, usually stiff, sometimes weak (subsp. chamissonis), verrucose, short and/or crisped hairs absent or sparse to abundant, cottony hairs absent, glands absent or sparse;
leaflets separate to ± overlapping, central obovate, 1–3.5(–4.5) × 0.5–2(–3) cm, usually petiolulate, petiolule to 5 mm, base cuneate, margins slightly revolute, distal ± 3/4 incised ± 1/2 to midvein, teeth (2–)3–4(–6) per side, ± approximate to distant, surfaces dissimilar, often strongly so, abaxial white to gray, long hairs 0.5–1.8 mm, cottony-crisped hairs ± dense, adaxial green, sometimes grayish green, long hairs sparse to abundant, short-crisped hairs sparse to abundant.
1–3.
(0–)1–2.
(1–)3–15(–20)-flowered, loosely cymose, sometimes racemiform.
1–7(–15)-flowered.
1–4(–5) cm, ± recurved in fruit.
1.5–5 cm in flower, to 6(–10) cm in fruit.
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 linear-lanceolate to lanceolate-elliptic, 2–5(–7) × 0.4–1.2(–1.5) mm, 1/4–1/2 as wide as sepals, margins usually flat, red glands absent or sparse and inconspicuous;
hypanthium 3–5 mm diam.;
sepals 3–6(–8) mm, apex acute;
petals 4–7(–10) × 4–7(–9) mm, ± longer than sepals;
filaments 0.8–1 mm, anthers 0.4 mm;
carpels 28–40, apical hairs absent, styles conic-columnar, strongly papillate-swollen in proximal 1/5–1/3, 1–1.5 mm.
(1.3–)1.5–1.9 mm, smooth, often ± carunculate.
1.1 mm.
= 70.
Potentilla plattensis
Potentilla arenosa
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.)
Subspecies 2 (2 in the flora).
The name Potentilla arenosa is now used for most arctic and subarctic plants previously treated as P. hookeriana or P. nivea subsp. hookeriana (Lehmann) Hiitonen. As noted by J. Soják (1986), the type of P. hookeriana has quinate leaves; that name is now restricted to a Rocky Mountain species in sect. Rubricaules. The arctic and subarctic material was briefly (1989–1999) called P. nivea, as discussed under that species. Because the type of P. nivea var. arenosa and other northern Asian specimens correspond closely to the North American plants, the name P. arenosa is assigned here.
The two subspecies differ only in one character, the petiole hairs, but are largely allopatric. Subspecies arenosa occurs in western and northern Greenland, northern North America (very northern in the east), and northern Asia (and perhaps northeasternmost European Russia); subsp. chamissonis occurs in southern Greenland, northeastern North America (more southern than subsp. arenosa), and northern Europe at least east to the Urals.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Petioles with common to abundant short and/or stiff crisped hairs in addition to long verrucose hairs. | subsp. arenosa |
1. Petioles with sparse or no short and/or soft crisped hairs in addition to long verrucose hairs. | subsp. chamissonis |
OR
Flora NW
PNW Herbaria
SW CO Wildflowers
WildflowerSearch
iNaturalist
USDA Plants Database
