Potentilla anserina
Potentilla sect. Pentaphylloides
common silverweed, Pacific cinquefoil, silver weed cinquefoil, silverweed
prostrate [to erect], flagelliform [or not], rooting at nodes [or not], lateral to ± persistent basal rosettes, 1–10+ dm, lengths (0.5–)1–5+ times basal leaves.
basal not or ± 2-ranked;
cauline (between flowering and/or rosette-forming nodes) 0–1;
primary leaves pinnate (distal leaflets sometimes confluent), (1–)3–50(–75) cm;
petiole: long hairs absent or ascending to weakly appressed, sometimes spreading, soft to weak, glands absent or very sparse;
primary leaflets (5–)7–21(–31[–51]) plus additional small leaflets interspersed, on distal (1/2–)2/3–4/5+ of leaf axis, overlapping or not, elliptic to obovate, margins revolute or nearly flat, distal (1/2–)2/3–3/4+ evenly incised 1/4–1/2 to midvein, teeth (2–)5–12(–16) per side, surfaces similar to strongly dissimilar, abaxial usually white, sometimes green, cottony(/crisped) hairs usually dense, sometimes sparse or absent, adaxial green to white, not glaucous, long hairs absent or weak to soft.
petiole (0.5–)1–15(–25) cm, long hairs absent or sparse to dense, 1.5–3.5 mm;
larger leaflets (0.4–)0.5–5(–7) × (0.2–)0.3–2(–3) cm, surfaces: abaxial with long hairs absent or sparse to abundant, not restricted to veins, 0.5–2(–2.5) mm, cottony-crisped hairs usually dense or usually absent (in subsp. groenlandica), adaxial with long hairs absent or sparse to abundant, cottony-crisped hairs usually absent, sometimes sparse to common (especially subsp. yukonensis).
solitary flowers at stolon nodes [± cymose].
straight in fruit, (1–)2–45(–55) cm.
epicalyx bractlets narrowly to broadly ovate-triangular or linear to elliptic, (2–)2.5–7(–8) × (0.3–)0.5–3(–3.5) mm, often 2-fid or dentate;
sepals (3–)3.5–7(–9) mm, apex subacute to acuminate;
petals (4–)5–15(–20) × (2.5–)3–10(–12) mm;
filaments (1–)2.5–3.5(–4.5) mm, anthers 0.7–1.3 mm;
carpels (10–)20–200(–250).
5(–7)-merous;
hypanthium 3–7 mm diam.;
petals bright yellow, elliptic to broadly elliptic, (4–)5–15(–20) mm, longer than sepals, apex rounded or slightly retuse;
stamens [5–]20(–30);
styles ± lateral [subapical or sub-basal], narrowly columnar-filiform, not papillate-swollen proximally, 1.5–2.5 mm.
2 mm.
slightly rugose and papillate.
Potentilla anserina
Potentilla sect. Pentaphylloides
Subspecies 4 or 5 (4 in the flora).
Potentilla anserina is polymorphic in most features, especially in hairiness, but also in size and in degree of dissection of leaflets, epicalyx bractlets, and sepals. While most of the variation described by A. G. Blytt (1906) is taxonomically insignificant, A. Rousi (1965) found support for three northern races: subspp. anserina, egedei, and pacifica. He also suggested that P. yukonensis Hultén might qualify as a separate subspecies. This treatment follows J. Soják (1994) in accepting four northern subspecies of P. anserina, all present in North America.
A. Rousi (1965) demonstrated partial interfertility between the races of Potentilla anserina, which form intermediates in all zones of contact. The distinctness of the four races, in spite of intermediates, is upheld by being partly allopatric and occupying different habitats where they are sympatric. As partly interfertile parapatric entities, they are best treated as subspecies.
The vast majority of chromosome counts are tetraploid. Tetraploid plants (2n = 28) are fully fertile; hexaploids (2n = 42) are largely pollen and seed sterile; pentaploids (2n = 35) are probably occasional hybrids (S. Erlandsson 1942, 1942b; A. Rousi 1965). A. Kurtto et al. (in J. Jalas et al. 1972+, vol. 13) considered numbers above tetraploid level as cases of occasional autopolyploidy.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Species ca. 50 (1 in the flora).
The use here of sect. Pentaphylloides is contrary to the argument by J. Soják (2007) that the use of Pentaphylloides Tournefort by G. R. Boehmer (in C. G. Ludwig 1760) qualified as an unranked infrageneric taxon, making sect. Pentaphylloides Tausch a later homonym. In that Boehmer was citing synonyms, not infrataxa, sect. Pentaphylloides Tausch is the correct name for this section. The names sect. Chenopotentilla Focke and sect. Leptostylae (Th. Wolf) Guşuleac are superfluous and illegitimate.
Potentilla anserina is the atypical and only representative in North America of a primarily southeastern Asian section. Although provisionally retained within Potentilla, the morphological distinctiveness of the section has led to the recognition of Argentina as a segregate genus (for example, P. A. Rydberg 1908d; Á Löve and D. Löve 1975b; B. C. Johnston 1985; J. Soják 2010). Molecular analyses (C. Dobeš and J. Paule 2010; M. H. Töpel et al. 2011) have confirmed the section is a strongly supported monophyletic clade, albeit including some other Asian species treated by J. Soják (1994) as the segregate genera Piletophyllum (Soják) Soják and Tylosperma Botschantzev. Chloroplast markers (Dobeš and Paule; Töpel et al.) place this clade sister to all other Potentilleae; nuclear markers (Töpel et al.) indicate instead a sister relation to Fragariinae.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Epicalyx bractlets equal to or longer than sepals, often 2-fid or dentate; leaflet surfaces: abaxial with cottony-crisped hairs dense, long hairs common to abundant, on and between veins, adaxial glabrous or sparsely to densely hairy; achenes with dorsal groove; inland and seashore plants | → 2 |
1. Epicalyx bractlets shorter than sepals, usually entire, rarely 2-fid or dentate; leaflet surfaces: abaxial with cottony-crisped hairs absent or sparse to dense, long hairs absent or sparse, on veins, adaxial usually glabrous, rarely sparsely to densely hairy; achenes without dorsal groove; seashore or near-coastal plants | → 3 |
2. Hypanthium patelliform (wider than deep) in fruit; epicalyx bractlets narrowly to broadly ovate-triangular, equal to sepals; most of North America. | subsp. anserina |
2. Hypanthium turbinate (± as deep as wide) in fruit; epicalyx bractlets usually linear to elliptic, longer than sepals, rarely subequal; interior w Canada and Alaska. | subsp. yukonensis |
3. Carpels (20–)50–200(–250); leaves (3–)10–50(–75) cm; leaflets (4–)5–10(–15) per side, abaxial surfaces densely hairy, teeth (4–)6–12(–16) per side, teeth apices acute to acuminate, rarely subacute; flowers 1–2.5(–3.5) cm diam. | subsp. pacifica |
3. Carpels 25–60; leaves (1–)2–10 cm, rarely longer; leaflets 2–4(–5) per side, abaxial surfaces glabrous, sometimes sparsely to densely hairy, teeth 2–6(–10) per side, teeth apices rounded to subacute; flowers 0.8–1.5 cm diam. | subsp. groenlandica |
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