Potentilla nivea
Potentilla pedersenii
potentille des neiges, snow cinquefoil, snowy cinquefoil
stout, not columnar, not sheathed with marcescent whole leaves.
not sheathed with marcescent whole leaves.
ascending to erect, (0.3–)0.5–3(–4) dm, lengths 1.5–2.5(–4) times basal leaves.
ascending to nearly erect, 0.4–2 dm.
(1–)3–10(–15) cm;
petiole (0.5–)1–6(–10) cm, long hairs usually absent, sometimes sparse to common (less so than cottony hairs), ± appressed, 1–2 mm, soft, smooth, short-crisped hairs absent or obscured, cottony hairs abundant to dense sometimes sparse with age, glands absent, sparse, or obscured;
leaflets overlapping, central obovate, 0.5–2(–4) × (0.2–)0.4–1.2(–2) cm, subsessile, base cuneate, margins slightly revolute, distal ± 3/4 incised (1/4–)1/3–1/2 to midvein, teeth (2–)3–5(–6) per side, ± approximate, surfaces dissimilar, often strongly so, abaxial ± white, long hairs 0.8–1.2 mm, cottony-crisped hairs dense, adaxial usually green, sometimes grayish green, long hairs sparse to abundant, short-crisped hairs sparse to common.
often both ternate and palmate or subpalmate on same plant, 2.5–4 cm;
petiole 1.5–2.5 cm, long hairs common to abundant, loosely appressed to ascending-spreading, 1–2 mm, weak to ± stiff, verrucose, crisped(/short) hairs absent or sparse to common, cottony hairs absent, glands sparse to common;
leaflets 3–5, proximalmost separated by 0–2 mm, central broadly elliptic to obovate, 1–1.5 × 0.5–0.9 cm, petiolules 1–2 mm, distal 2/3–3/4 of margin incised 1/2–3/4 to midvein, teeth (2–)3–4 per side, 4–6 mm, apical tufts ± 1 mm, abaxial surfaces grayish white to white, long hairs abundant (sometimes obscuring entire surface), cottony-crisped hairs abundant to dense, short hairs absent or obscured, glands sparse to common but usually obscured, adaxial grayish green to gray, long hairs sparse to abundant, 1–1.5(–2) mm, ± weak, short (short-crisped) hairs absent or sparse, rarely common, cottony hairs absent, glands absent or sparse, rarely common.
0–1.
0–2.
1–5(–7)-flowered.
(1–)3–7-flowered, open, branch angle 30–50°.
1–4 cm in flower, to 5 cm in fruit.
1–2 cm, proximal to 4 cm.
epicalyx bractlets narrowly to broadly lanceolate or elliptic, (2–)4–7 × 0.6–1.7 mm, usually 1/4–1/2 as wide as sepals, margins flat, red glands usually absent, sometimes sparse, inconspicuous;
hypanthium (2–)3–4 mm diam.;
sepals (2.5–)4–8 mm, apex acute;
petals (3–)4–8 × (3–)5–9 mm, slightly longer than sepals;
filaments 0.9–1.2 mm, anthers 0.5 mm;
carpels 20–40, apical hairs absent, styles narrowly columnar or columnar-tapered, strongly papillate-swollen at very base, rarely in proximal 1/5–1/3, 0.7–1.2 mm.
epicalyx bractlets narrowly ovate to elliptic, 4–5 × 1–1.4 mm;
hypanthium 3–4 mm diam.;
sepals 4–6 mm, apex subacute to acute, glands sparse to common, usually not obscured;
petals pale yellow, usually not overlapping, 6–7 × 4–8 mm, distinctly longer than sepals;
filaments 1–2 mm, anthers ± 0.4 mm;
carpels 40–80, styles 0.8–0.9 mm.
1.1–1.5 mm.
1.1–1.2 mm.
= 56, 63; 28, 42, 49, 70 (Asia, Europe).
Potentilla nivea
Potentilla pedersenii
Although now restricted to plants with exclusively (or at least predominantly) cottony hairs on the petioles, the name Potentilla nivea has a long history with an often wider application, sometimes including nearly all of sect. Niveae. As further confusion, J. Soják (1989) noted that the Linnaean type of P. nivea belonged to what is here treated as P. arenosa. Although historical usage of P. nivea has been re-established as a conserved name with a conserved type (B. Eriksen et al. 1999), from 1989 to 1999 the name P. nivea was applied to P. arenosa. During this period, P. prostrata subsp. floccosa was briefly adopted as the correct name for this species (for example, W. J. Cody 1996).
Molecular evidence (B. Eriksen and M. H. Töpel 2006) indicates that populations of Potentilla nivea in the Atlantic regions, including Greenland and eastern Canada, differ from those in the Beringian regions of northwestern North America, suggesting expansion from separate Pleistocene refugia. A comparable pattern was noted by R. Elven and S. G. Aiken (2007) based on morphologic characters. The conserved type of P. nivea is from northern Sweden (Eriksen et al. 1999) and belongs to the Atlantic morphologic group. The variation within each region is large, and racial recognition would accordingly be premature. Plants from sites south of the continental glaciation, which were not included in the analysis by Eriksen and Töpel, deviate in having acuminate leaflet teeth and epicalyx bractlets and in being generally more slender. Epicalyx bractlets of some Washington plants are nearly as narrow as those of P. crebridens.
Additional chromosome numbers have been reported for Potentilla nivea, but it is unknown whether these apply to this species, P. crebridens, some Asian relative, or hybrids.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Potentilla pedersenii and P. uschakovii account for the majority of arctic populations previously included in a broadly defined P. rubricaulis. The diagnostic morphological characters between the two species can be variable and overlapping; they are treated separately in part because of differences in presumed parental combinations. Whereas P. pulchella is the probable sect. Pensylvanicae parent for both species, the putative sect. Niveae parent for P. pedersenii is P. arenosa subsp. arenosa; that of P. uschakovii is P. subvahliana. Reflecting this parentage, P. pedersenii is distinguished by caudex branches with no marcescent whole leaves, verrucose long hairs on petioles, and inflorescences with usually several relatively small flowers. In contrast, P. uschakovii often has marcescent whole leaves sheathing the caudex branches, smooth long hairs on petioles, and one- or few-flowered inflorescences with mostly larger flowers. These generalities aside, there is much variation within both species, such that each island or population group may have its own features; it is probable that both P. pedersenii and P. uschakovii have evolved from multiple hybridization events.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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