Potentilla sect. Rivales
Rosaceae tribe Potentilleae
decumbent to erect, sometimes prostrate, not flagelliform, not rooting at nodes, from centers of ephemeral basal rosettes, (1–)2–6(–9) dm, lengths (1–)2–5(–12) times basal leaves.
basal not in ranks;
cauline (0–)1–9(–14);
basal and proximal cauline ternate or palmate to pinnate (with distal leaflets ± confluent), (2–)3–15(–25) cm;
petiole: long hairs ascending to spreading, rarely appressed, weak to stiff, glands absent or sparse to abundant;
leaflets 3–9, at tip to distal 2/3 of leaf axis, separate to overlapping, oblanceolate or elliptic to obovate, sometimes oval or nearly round, margins flat, distal 1/2 to ± whole length evenly to unevenly incised 1/4–1/2 to midvein, teeth (2–)3–8(–15) per side, surfaces ± similar, green (abaxial often paler), not glaucous, long hairs weak to stiff, cottony hairs absent.
alternate, rarely opposite, pinnately (palmately) compound (simple in Alchemilla, Aphanes, and Chamaerhodos);
stipules persistent (absent in Chamaerhodos), adnate to petiole;
venation pinnate or palmate.
(5–)20–100+-flowered, ± cymose, sometimes racemiform, compact to open.
straight to ± recurved in fruit, 0.2–2(–3) cm, proximal often ± longer than distal.
5-merous;
hypanthium (2–)3–6(–7) mm diam.;
petals pale yellow to yellow, broadly oblanceolate to oblong or broadly obovate, (1–)1.5–5 mm, usually shorter than sepals, apex rounded to ± retuse;
stamens (5–)10–20(–25);
styles subapical, conic-tapered, slightly to strongly papillate-swollen ± whole length, 0.5–0.8 mm.
perianth and androecium perigynous;
epicalyx bractlets present, sometimes absent;
hypanthium usually patelliform, cupulate, or campanulate, sometimes turbinate, saucer-shaped, flat-bottomed, or subglobose to ellipsoid or ovoid;
torus flat to conic or turbinate, enlarged (absent or reduced in Alchemilla, Aphanes, and Chamaerhodos);
carpels 1–260, styles basal or lateral to subterminal, distinct;
ovules 1(or 2), basal.
aggregated achenes (achenes in Alchemilla and Aphanes);
torus sometimes fleshy;
styles deciduous or persistent, not elongate.
smooth to strongly rugose.
Potentilla sect. Rivales
Rosaceae tribe Potentilleae
Species 18–21 (4 in the flora).
The North American representatives of sect. Rivales are morphologically distinctive in being annuals, biennials, or short-lived perennials (especially in cold regions) with very short, conic-tapered styles. Plants grow primarily in wet habitats, especially where periodically inundated. These distinctions led E. L. Greene (1906c) to adopt Tridophyllum. However, the gross morphological cohesiveness is not matched by molecular monophyly. Instead, chloroplast data scatter Potentilla norvegica, P. rivalis, and P. supina among the core Potentilla, while P. biennis is sister species to the monophyletic Ivesia-Horkelia-Horkeliella clade (C. Dobeš and J. Paule 2010; M. H. Töpel et al. 2011). Nuclear markers, on the other hand, place P. norvegica as sister to the Ivesia-Horkelia-Horkeliella clade (Töpel et al.), suggesting a possible hybrid origin and/or multiple origins of the biennial habit.
Existing herbarium annotations of Potentilla biennis, P. norvegica, and P. rivalis are not reliable, but the three species can be readily distinguished by vestiture of proximal petioles and stems. Only P. biennis has prominently septate gland-tipped trichomes; P. norvegica is characterized by relatively stiff, spreading, tubercle-based hairs to 3 mm, resembling those of P. recta. In addition, the tiny, smooth, pale achenes of P. biennis and P. rivalis contrast sharply with the larger, darker, strongly ridged ones of P. norvegica.
Basal leaves usually wither by anthesis, and cauline leaves (that is, those proximal to the first flowering and/or branching node) often wither by mid-anthesis as well. Unless otherwise indicated, leaves include both basal and cauline leaves. If leaves are ephemeral, and/or where stems branch at the proximal nodes, proximal inflorescence bracts can be used as leaf-equivalents in the keys and descriptions.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Genera 14–22, species ca. 860 (14 genera, 189 species, including 1 hybrid, in the flora area).
The base chromosome number for Potentilleae is mostly x = 7 (8 in Alchemilla and Aphanes; 14 in Comarum).
Variation in the number of genera recognized in Potentilleae is due to differences in generic delimitation between D. Potter et al. (2007) and the authors of Potentilla and segregates here (see 9. Ivesia and 8. Potentilla for discussion). In the former, Duchesnea, Horkelia, Horkeliella, and Ivesia are included within Potentilla. Likewise, Aphanes is included within Alchemilla by Potter et al. while it is kept distinct here.
Potentilla and its segregates and Fragaria are host to Phragmidium rusts, but not the other genera of the tribe.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Leaves pinnate to subpalmate, leaflets 5–9 | → 2 |
1. Leaves ternate or palmate, leaflets 3–5 | → 3 |
2. Leaflets 5–9, on distal (1/4–)1/2–2/3 of leaf axis; achenes usually strongly rugose, developing a smooth, corky protuberance often as large as body of achene. | P. supina |
2. Leaflets 5(–7), on less than distal 1/5 (basal leaves) or 1/2 (cauline leaves) of leaf axis; achenes ± smooth, without a corky protuberance. | P. rivalis |
3. Petiole and stem base hairs usually ± stiff, 1–2.5(–3) mm, glands absent or sparse, inconspicuous; achenes usually strongly rugose, tan to brown, 0.8–1.3 mm; hypanthia 4–7 mm diam.; stamens 15 or 20, anthers 0.3–0.5 mm. | P. norvegica |
3. Petiole and stem base hairs usually ± weak, 0.5–1.5 mm (very weak if longer), glands absent or sparse to abundant, sometimes conspicuous; achenes ± smooth, white to yellowish, 0.5–0.9 mm; hypanthia (2–)3–4(–5.5) mm diam.; stamens (5–)10 or 15, anthers 0.2–0.3 mm | → 4 |
4. Petiole and stem base glands absent or sparse, inconspicuous; leaflets oblanceolate-elliptic to obovate, separate to ± overlapping; stems decumbent to erect, sometimes prostrate. | P. rivalis |
4. Petiole and stem base glands sparse to abundant, conspicuous (to 1 mm, septate); leaflets mostly obovate or oval to nearly round, usually overlapping; stems ascending to erect. | P. biennis |
1. Shrubs; leaf lobe margins entire; achenes hirsute. | Dasiphora |
1. Herbs, perennial, sometimes annual or biennial, or subshrubs; leaf lobe margins or apices ± toothed, sometimes entire; achenes glabrous (sometimes ± hairy) | → 2 |
2. Petals 0, sepals 4; achenes 1, enclosed in dry, urceolate or subglobose to ellipsoid or ovoid hypanthia | → 3 |
2. Petals and sepals usually 5; achenes 1–260, usually aggregated (sometimes on elongating tori), usually in (± open) patelliform, cupulate, campanulate, or turbinate hypanthia (not enclosed in dry hypanthium) | → 4 |
3. Herbs perennial; leaves basal, blades reniform to orbiculate, palmately lobed, sometimes palmately compound; stamens 4. | Alchemilla |
3. Herbs annual; leaves cauline, blades cuneate, deeply divided into segments, each lobed; stamen 1(or 2). | Aphanes |
4. Leaves all or mostly basal or proximal (if cauline, deeply pinnatifid), ternate or 2–4-ternate (sometimes simple and coarsely toothed apically in Sibbaldia) | → 5 |
4. Leaves basal or cauline, the latter usually reduced distally, odd-pinnate to palmate, rarely ternate or ± bipinnate | → 9 |
5. Tori becoming red and fleshy in fruit; leaf margins serrate to crenate | → 6 |
5. Tori hemispheric (not enlarged or fleshy) in fruit or absent; leaf margins entire or (2–)3(–5)-toothed apically | → 7 |
6. Leaves ± doubly serrate or crenate; stolons leafy; inflorescences: flowers solitary, axillary at stolon nodes; petals yellow. | Duchesnea |
6. Leaves serrate to crenate; stolons not leafy; inflorescences 1–10-flowered, cymes, axillary from leaf rosettes; petals usually white. | Fragaria |
7. Leaves pinnately compound or simple and deeply pinnatifid, margins entire, stipules absent. | Chamaerhodos |
7. Leaves ternate, margins toothed apically, stipules persistent | → 8 |
8. Petals ± yellow; stamens 5. | Sibbaldia |
8. Petals usually white; stamens 20(–30). | Sibbaldiopsis |
9. Petals deep red to purple, rarely pink, shorter than sepals; tori enlarged and spongy at maturity; horizontal stems sometimes floating, wetland habitats. | Comarum |
9. Petals yellow to white, rarely pink or red (then equal to or longer than sepals); tori not enlarged and spongy at maturity; stems erect to decumbent, not horizontal or floating even if in wetlands | → 10 |
10. Anthers dehiscing by continuous marginal slit (with a single theca); styles sub-basal. | Drymocallis |
10. Anthers dehiscing longitudinally; styles subterminal to lateral | → 11 |
11. Hypanthium patelliform to campanulate or cupulate to turbinate (not flat-bottomed); filaments not forming tube; petals white to yellow, sometimes reddish or pink tinged | → 12 |
11. Hypanthium ± cupulate or bluntly campanulate and flat-bottomed; filaments forming tube; petals usually white, sometimes pink-tinged, rose-veined, or cream | → 13 |
12. Plants not aromatic; leaves ± cordate or reniform to narrowly elliptic in outline, leaflets 3–15(–41); petals oblanceolate or obovate to obcordate to nearly round, rarely elliptic; carpels 3–260. | Potentilla |
12. Plants often aromatic; leaves planar to cylindric, leaflets (3–)7–161; petals linear or narrowly oblanceolate to obovate, sometimes obcordate; carpels 1–20(–40). | Ivesia |
13. Stamens 10; leaflets (3–)5–41. | Horkelia |
13. Stamens 20; leaflets 30–70. | Horkeliella |
