Potentilla

Herbs, perennial, rarely annual or biennial, rosetted to densely matted, 0.1–7(–10) dm, sparsely to densely hairy hairs straight, crisped, and/or cottony, sometimes glabrate, sometimes glandular; usually short-rhizomatous, sometimes stoloniferous. Stems 1–many, prostrate to erect, sometimes rooting at nodes, usually ± green, sometimes reddish. Leaves winter marcescent or persistent, primarily basal or cauline, cauline (0–)1–9, reduced or well-developed, alternate, rarely opposite, ternate, palmate, subpalmate, or odd-pinnate, sometimes ± bipinnate; stipules persistent, basally adnate to petiole, linear to ovate, margins entire or lobed, sometimes toothed; petiole present; blade ± cordate or reniform to narrowly elliptic in outline, 0.5–25(–30) cm, foliaceous, rarely ± coriaceous; leaflets 3–15(–41), terminal sometimes confluent with distalmost lateral ones, separate to overlapping, narrowly oblanceolate to obovate, elliptic, oblong, cuneate, or flabellate in outline, margins flat or revolute, toothed to divided nearly to base into linear to oblanceolate lobes, sometimes entire, venation pinnate or palmate. Inflorescences terminal, sometimes axillary on stolons, 1–100+-flowered, often cymose, sometimes solitary or racemiform, open to ± congested; bracts present, usually ± reduced; bracteoles absent. Pedicels present, straight or becoming ± recurved in fruit. Flowers (5–)8–20(–26) mm diam.; epicalyx bractlets (4 or)5(–10); hypanthium patelliform to cupulate, rarely turbinate, 0.5–2.5(–5) × (1.5–)2–7(–10) mm; sepals (4 or)5(–10), spreading at anthesis, lanceolate to broadly ovate or deltate; petals (4 or)5(–10), pale to bright yellow, less often dark reddish, reddish orange, or white, oblanceolate or obovate to most commonly obcordate to nearly round, rarely elliptic (sect. Pentaphylloides); stamens (5–)20(–30), shorter than petals; filaments not forming tube; torus ± conic; carpels 3–260, glabrous, rarely sparsely hairy, styles usually subapical, rarely lateral; ovule 1. Fruits aggregated achenes, individually deciduous, 1–260, obliquely ± ovoid, 0.5–2.6 mm, glabrous or rarely ± hairy apically or on style scar; hypanthium persistent; sepals persistent, erect; styles tardily deciduous, jointed, filiform to conic, sometimes clavate, often rough-thickened basally to nearly whole length. x = 7.

Distribution

North America, Mexico, West Indies, Bermuda, Central America, South America, Eurasia, Africa, Atlantic Islands (Azores, Macaronesia), Pacific Islands (New Guinea, New Zealand), Australia, arctic, temperate, and montane in Northern Hemisphere, mostly montane in Southern Hemisphere and equatorial regions.

Discussion

Species ca. 400 (98, including 1 hybrid, in the flora).

Potentilla as presented here has a circumscription significantly reduced from treatments in most recent floras, since the convergence of morphologic (J. Soják 1985[1989], 2008) and molecular (T. Eriksson et al. 1998, 2003; C. Dobeš and J. Paule 2010; M. H. Töpel et al. 2011) interpretations has justified the segregation of P. fruticosa, P. glandulosa and relatives, P. palustris, and P. tridentata into Dasiphora, Drymocallis, Comarum, and Sibbaldiopsis, respectively (A. Kurtto and Eriksson 2003; Ertter 2007). The generic assignment of P. anserina is problematic (Soják 2010); the species is retained here within Potentilla. The senior author has chosen to maintain Duchesnea, Horkelia, Horkeliella, and Ivesia as distinct genera. As a result, the generic arrangement used here nearly recapitulates that used by P. A. Rydberg (1898, 1908d), representing the last comprehensive treatment of Potentilleae in North America.

Species circumscriptions and nomenclature are also significantly revised, reflecting not only the first continental assessment of the genus since Rydberg but also the need to synthesize American and Eurasian approaches to the genus. Whereas P. A. Rydberg’s (1908d) revision has served as the basis for subsequent floristic works in North America, subject to significant lumping of species and realignment of genera (for example, D. D. Keck 1938; J. Clausen et al. 1940), Eurasians generally have used as their starting point a monograph by T. Wolf (1908), a contemporary of Rydberg. Rydberg was handicapped by limited access to type material in Europe, resulting in the misapplication of several names.

Even with the reduced generic circumscription and improved global perspective, Potentilla remains challenging. Key contributing factors are facultative pseudogamous agamospermy and hybridization (summarized by J. Clausen et al. 1940; B. Eriksen 1996), which result in everything from ephemeral F1 hybrids to fully stabilized species of hybrid origin, sometimes across sectional boundaries. In the face of such biosystematic complexity, this treatment uses the operational species concept for arctic species outlined by R. Elven et al. (1999), with the exception that variety has been used as the primary infraspecific rank for temperate species.

Several species have been recently described or resurrected from synonymy for use in the current treatment, and anomalous collections examined during this preparation probably represent additional novelties. The isolated mountain ranges and complex geology of the North American Cordillera in particular contains a rich trove of unresolved diversity. Collectors should be alert for sympatric species in these situations, and the possible hybrid origin of aberrant individuals or clones.

Sections that have been established for North American Potentilla [for example, by A. Nelson (in J. M. Coulter and Nelson 1909), O. A. Stevens 1959, B. C. Johnston 1985] are mostly based on a subset of validly published but unranked groups by P. A. Rydberg (1898, 1908). Species numbers for primarily Eurasian sections have been provided by J. Soják (pers. comm.). The sectional arrangement used here is both pragmatic and tentative; it also represents an implicit phylogenetic hypothesis. The arrangement reflects molecular analyses (C. Dobeš and J. Paule 2010; M. H. Töpel et al. 2011), in which the first four sections correspond to well-supported clades that diverge basal to the ivesioid clade and the remaining sections. The majority of species beyond the first six sections are mingled in a largely unresolved crown clade, informally termed the Potentilla core group by Dobeš and Paule, and the Argentea clade by Töpel et al. Their results also suggest an Asian origin for Potentilla in the Oligocene, multiple colonizations in North America, and rapid radiation of the core group beginning in the Pliocene.

Detailed morphology and anatomy in Potentilla are provided by P. A. Rydberg (1898) and T. Wolf (1908). With some exceptions, floral morphology is of less taxonomic value than are leaf division and leaflet incision, particularly of basal leaves, which renders specimens without them often impossible to identify correctly. Habit and inflorescence architecture are also important features, such that specimens with fully developed inflorescences are typically more confidently identifiable than those in early anthesis.

Vestiture, especially of petioles and abaxial leaflet surfaces, is of critical diagnostic importance. Four primary hair groups are recognized by B. Eriksen and B. A. Jurtzev (1999): straight (or curved), crispate (short, twisted hairs, called crisped in the current treatment), floccose (corresponding to cottony in FNA terminology), and glandular (mostly short-stipitate). We further divide straight hairs into short hairs 0.2 mm, which sometimes form an even underlayer to other hair types, and long hairs for all other straight to curved hairs. Because these five groups can occur in any combination, all are addressed separately in descriptions. Hair density is categorized as sparse, common (or moderately), abundant, or dense if obscuring the surface; rigidity of long hairs is categorized as soft, weak, or stiff.

In keys and descriptions, stem length includes inflorescence, hairs are eglandular, and leaves are basal unless otherwise indicated. Rosetted plants have a basal rosette of leaves from a largely unbranched caudex; tufted plants have multiple stems from a short-branched caudex; and matted plants have dense, spreading, multi-branched caudices. Stolons and stoloniferous are used for plants that sprawl on the ground with apparently solitary flowers arising from nodes of flagelliform stems, even though these may be more homologous to prostrate cymose inflorescences than true stolons. Flagelliform stems form short shoots at the nodes but usually are not otherwise branched. In plants with stems arising centrally from ephemeral basal rosettes, new basal rosettes for the following year often appear in fall and might be confused with persistent rosettes. The diagnostic character of marcescent whole leaves (in sects. Niveae and Rubricaules) is in addition to sheathing stipular leaf bases and petioles, which are also commonly present on plants lacking marcescent whole leaves. Transitions between the extremes of strictly palmate and strongly pinnate leaves are roughly quantified as a fraction of the leaf axis (petiole plus rachis) bearing leaflets. Cauline leaves consist of foliar and bractlike structures on the stem proximal to the proximalmost branch. Leaflet dimensions and teeth number are of the larger leaflets (central in palmate leaves, terminal or distal in pinnate leaves). Leaflet tooth length is measured on the distal edge of the largest and medium-sized teeth. The central portion of the leaflet between opposite tooth sinuses is called the undivided medial blade. Hairs projecting beyond the tips of the leaflet teeth are referred to as apical tufts. Pedicel length is measured from the flower to the subtending bract, even if this appears to be a mid-pedicel bract. Because pedicels at the proximal nodes are often significantly longer than elsewhere, pedicel length is primarily for the nonproximal nodes, with the proximalmost extremes noted separately. Curved pedicels are those that commonly become sigmoidally recurved in fruit; this is characteristic of sections with predominately prostrate inflorescences. Measurements of pedicels, epicalyx bractlets, hypanthia, and sepals are taken at flowering and fruiting but not in bud. Hypanthium diameter is an external measurement of pressed flowers. Although not otherwise indicated, petals of most species commonly have a basal patch of more intense color, which often coincides with ultraviolet nectar guides (N. Naruhashi and H. Ikeda 1999). Style features are based primarily on dried mature styles that are tardily deciduous. Rugose achenes are often smooth until mature.

Selected References

Dobeš, C. and J. Paule. 2010. A comprehensive chloroplast DNA-based phylogeny of the genus Potentilla (Rosaceae): Implications for its geographic origin, phylogeography and generic circumscription. Molec. Phylogen. Evol. 56: 156–175.

Rydberg, P. A. 1908d. Potentilla. In: N. L. Britton et al., eds. 1905+. North American Flora.... 47+ vols. New York. Vol. 22, 293–388.

Lower Taxa

Potentilla sect. Arenicolae, Potentilla sect. Aureae, Potentilla sect. Biflorae, Potentilla sect. Brevifoliae, Potentilla sect. Chrysanthae, Potentilla sect. Concinnae, Potentilla sect. Graciles, Potentilla sect. Leucophyllae, Potentilla sect. Lupinoides, Potentilla sect. Multijugae, Potentilla sect. Niveae, Potentilla sect. Pensylvanicae, Potentilla sect. Pentaphylloides, Potentilla sect. Potentilla, Potentilla sect. Rectae, Potentilla sect. Rivales, Potentilla sect. Rubrae, Potentilla sect. Rubricaules, Potentilla sect. Subjugae, Potentilla sect. Subviscosae, Potentilla sect. Terminales, Section

Key

1	Petals white or dark reddish to reddish orange	> 2
1	Petals pale to bright yellow, rarely cream	> 4
2	Petals dark reddish to reddish orange (see also Comarum, Ivesia multifoliolata).	Potentilla sect. Rubrae
2	Petals white (see also Sibbaldiopsis)	> 3
3	Leaves ternate; perennials.	Potentilla sect. Lupinoides
3	Leaves ± pinnate, sometimes ± bipinnate; biennials, sometimes annuals or short-lived perennials.	Potentilla sect. Arenicolae
4	Plants stoloniferous; stems flagelliform, becoming prostrate, rooting at some nodes; inflorescences solitary flowers at stolon nodes (see also Duchesnea)	> 5
4	Plants not stoloniferous; stems not flagelliform, usually decumbent to erect, sometimes prostrate or pendent, not rooting at nodes; inflorescences usually cymose, sometimes racemiform or solitary flowers	> 6
5	Leaves pinnate, usually white at least abaxially, sometimes green.	Potentilla sect. Pentaphylloides
5	Leaves ternate or palmate, usually ± green on both surfaces, sometimes silvery white abaxially.	Potentilla sect. Potentilla
6	Leaves ternate, appearing ± palmate, central leaflets incised nearly to base into 3 lobes, lateral ones incised nearly to base into 2 lobes, margins strongly revolute; Beringia.	Potentilla sect. Biflorae
6	Leaves ternate or palmate to pinnate, leaflets incised 1/10 (or less) to nearly to midrib into (0–)1–15+ teeth, margins flat or revolute; North America including Beringia	> 7
7	Styles 0.5–1.3(–1.5) mm, conic-tapered to columnar-tapered or columnar-clavate, rarely ± filiform	> 8
7	Styles (1–)1.5–3(–3.5) mm, filiform to tapered, rarely columnar	> 20
8	Stems from centers of ephemeral basal rosettes, primary leaves cauline; primarily ± disturbed or seasonally wet habitats	> 9
8	Stems lateral to persistent basal rosettes, primary leaves basal; primarily arctic, alpine, and prairie habitats	> 12
9	Annuals, biennials, or short-lived perennials; leaves ternate or palmate to pinnate; petals (1–)1.5–5 mm; styles slightly to strongly papillate-swollen ± whole length, 0.5–0.8 mm; primarily seasonally wet habitats.	Potentilla sect. Rivales
9	Perennials; leaves usually palmate, rarely ternate; petals (2–)2.5–10(–13) mm; styles not or ± papillate-swollen in proximal 1/5–1/2, 0.6–1.5 mm; primarily ± disturbed habitats	> 10
10	Flowers 4(–5)-merous; leaflets green abaxially.	Potentilla sect. Potentilla
10	Flowers 5-merous; leaflets green to white abaxially	> 11
11	Leaflets green abaxially, cottony and/or crisped hairs absent; petioles: long hairs stiff, spreading; hypanthia 5–9 mm diam.	Potentilla sect. Rectae
11	Leaflets green to white abaxially, crisped and/or cottony hairs absent or sparse to dense; petioles: long hairs soft to weak, loosely appressed to spreading; hypanthia 2–5 mm diam.	Potentilla sect. Terminales
12	Leaves pinnate to subpalmate	> 13
12	Leaves ternate or palmate	> 16
13	Styles papillate-swollen only at very base if at all; inflorescences ± congested to very open, sometimes solitary flowers	> 14
13	Styles papillate-swollen in proximal 1/5–3/4+; inflorescences congested to ± open, sometimes solitary flowers	> 15
14	Stems (0.2–)0.4–1(–1.5) dm; leaflets incised 1/2–3/4 to midvein, teeth 2–4(–5) per side; inflorescences (1–)2–5(–10)-flowered; Rocky Mountains.	Potentilla sect. Subjugae
14	Stems 1–5 dm; leaflets incised nearly to midvein, teeth (3–)4–7 per side; inflorescences 2–40-flowered; Alaska to Quebec.	Potentilla sect. Pensylvanicae
15	Leaflets on up to distal 1/6(–1/4) of leaf axis, usually grayish white to white abaxially, sometimes gray, cottony (or cottony-crisped) hairs abundant to dense.	Potentilla sect. Rubricaules
15	Leaflets on distal 1/6–1/2+, rarely less, of leaf axis, green to white abaxially, cottony hairs absent or sparse to dense.	Potentilla sect. Pensylvanicae
16	Leaflets gray to white abaxially, sometimes yellowish white or reddish, cottony(/crisped) hairs abundant to dense	> 17
16	Leaflets pale to dark green abaxially, sometimes reddish, grayish, or brownish, cottony hairs absent	> 18
17	Leaflets 3, rarely more, on all basal leaves.	Potentilla sect. Niveae
17	Leaflets 3–5(–7), usually more than 3 on at least some leaves.	Potentilla sect. Rubricaules
18	Leaves ternate; leaflets 3.	Potentilla sect. Aureae
18	Leaves usually palmate; leaflets (3–)5–11	> 19
19	Stem lengths usually 2–5 times basal leaves, rarely shorter than leaves; leaflet teeth 1–10(–13) per side; glands sometimes red.	Potentilla sect. Chrysanthae
19	Stem lengths l–3 times basal leaves; leaflet teeth 2–4(–5) per side; glands not red.	Potentilla sect. Aureae
20	Stems usually prostrate to decumbent, sometimes ascending (especially in supporting vegetation) or pendent, lengths 1/2–3(–5) times basal leaves; pedicels often recurved in fruit, proximal usually not much longer than distal; plants usually rosetted, sometimes tufted or ± matted; taproots sometimes fleshy-thickened	> 21
20	Stems decumbent to erect, rarely prostrate, lengths (1–)2–4(–5) times basal leaves; pedicels straight in fruit, proximal often much longer than distal; plants usually tufted, sometimes cushion-forming or matted, rarely rosetted; taproots not fleshy-thickened	> 25
21	Cottony hairs sparse to dense, at least on abaxial leaflet surfaces	> 22
21	Cottony hairs absent	> 23
22	Leaves pinnate; leaflets on distal 1/2–2/3(–3/4) of leaf axis, surfaces ± similar, adaxial hairs soft.	Potentilla sect. Multijugae
22	Leaves palmate to pinnate; leaflets usually on tip or to distal 1/2 of leaf axis, or, if more, then surfaces ± to strongly dissimilar, adaxial hairs stiff.	Potentilla sect. Concinnae
23	Leaves pinnate.	Potentilla sect. Multijugae
23	Leaves ternate or palmate to subpalmate	> 24
24	Petioles: straight hairs ± appressed, glands usually absent or sparse, rarely abundant.	Potentilla sect. Concinnae
24	Petioles: straight hairs usually spreading to ascending, sometimes loosely appressed, glands usually abundant, sometimes sparse.	Potentilla sect. Subviscosae
25	Leaves ternate; leaflets 3.	Potentilla sect. Aureae
25	Leaves usually palmate to pinnate; leaflets (3–)5–15(–41)	> 26
26	Leaves usually palmate to subpalmate, leaflets on tip or less than distal 1/10 of leaf axis	> 27
26	Leaves pinnate to subpinnate, or palmate with additional lateral leaflets; leaflets on distal 1/10 to nearly whole leaf axis	> 28
27	Styles (1–)1.5–3 mm; basal leaves 2-ranked or not, surfaces green to white, sometimes blue-green, sometimes glaucous; North America and Greenland, especially mid-montane w North America.	Potentilla sect. Graciles
27	Styles 1–1.6 mm; basal leaves 2-ranked, surfaces green, not glaucous; e Canada and Greenland, mostly coastal.	Potentilla sect. Aureae
28	Leaves usually palmate with additional lateral leaflets, sometimes pinnate; leaflets (3–)5 at tip of leaf axis plus 1(–2) additional pairs, distal leaflets distinct, surfaces strongly dissimilar; petioles: long hairs spreading on first-formed leaves, tightly appressed to ascending on later-formed leaves; 3400–4000 m.	Potentilla sect. Subjugae
28	Leaves pinnate to subpinnate with 3 apical leaflets and usually more than 2 additional pairs, distal leaflets often confluent, surfaces similar to strongly dissimilar; petioles: long hairs absent or weak to stiff, tightly appressed to spreading; 300–3800 m	> 29
29	Leaflets (3–)5–7(–9) on distal 1/10–1/2(–3/4) of leaf axis, surfaces ± similar, cottony hairs usually absent	> 30
29	Leaflets (5–)7–21(–41) on distal (1/6–)1/5–2/3 to whole rachis, surfaces similar to strongly dissimilar, cottony hairs often present	> 31
30	Stems (1–)1.5–5(–6) dm; glands usually absent or sparse, rarely abundant; basal leaves (2–)5–25(–28) cm; leaflets ± obovate to cuneate; petals 5–12 mm.	Potentilla sect. Graciles
30	Stems (0.2–)0.5–1.5(–2.5) dm; glands common to abundant; basal leaves 2–7 cm; leaflets ± flabellate; petals 3.5–6.5 mm.	Potentilla sect. Brevifoliae
31	Leaflets usually ± evenly incised 1/4–1/2 or less to midvein, sometimes entire; stems ascending to erect, (0.3–)1.5–7(–8) dm; proximal pedicels usually much longer than distal; Canadian prairies to s Nevada, Arizona, and New Mexico.	Potentilla sect. Leucophyllae
31	Leaflets evenly or unevenly incised 1/2 to completely to midvein, sometimes entire; stems usually prostrate to decumbent, sometimes ascending, (0.3–)0.5–3(–5) dm; proximal pedicels often not much longer than distal; Rocky Mountains w to California, Oregon, and Washington.	Potentilla sect. Multijugae