Potentilla sect. Potentilla
Rosaceae tribe Potentilleae
usually becoming ± prostrate, sometimes ascending to erect, often flagelliform, often rooting at nodes, lateral or central to persistent or ephemeral basal rosettes, 0.3–12+ dm, lengths (1–)2–10+ times basal leaves.
basal and cauline not in ranks;
cauline (proximal to flowering and/or branching nodes) 0–3(–7);
primary leaves ternate or palmate, 2–20(–30) cm;
petiole: long hairs appressed to spreading, weak to stiff, glands absent or sparse, sometimes common;
leaflets 3–5(–7), at tip of leaf axis, separate to slightly overlapping, obovate to narrowly elliptic, cuneate, or oblanceolate, margins flat or slightly revolute, distal 1/2–3/4 evenly incised 1/4–1/2 to midvein, teeth 2–13 per side, surfaces similar to ± dissimilar, abaxial usually green, sometimes silvery white, cottony hairs absent, adaxial green, not glaucous, long hairs usually ± stiff, sometimes weak or 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.
solitary flowers at stolon nodes or 3–30-flowered, cymose, open.
straight or slightly curved in fruit, (1–)2–12(–17) cm, proximal not longer than distal.
4–5(–10)-merous;
hypanthium 1.5–5(–7) mm diam.;
petals usually bright yellow, rarely cream, ± obcordate or obovate to round, (2–)4–9(–12) mm, usually longer than sepals, apex rounded to retuse;
stamens 15–20;
styles subapical, columnar-clavate to ± filiform, not papillate-swollen proximally, 0.6–1.5 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 or rugose.
Potentilla sect. Potentilla
Rosaceae tribe Potentilleae
Species 7 or 8 (5 in the flora).
The species of sect. Potentilla comprise a monophyletic clade that includes Duchesnea, diverging basally to the species placed here in Horkelia, Horkeliella, and Ivesia (C. Dobeš and J. Paule 2010; M. H. Töpel et al. 2011). There are at least some morphological features by which this and other clades basal to the core Potentilla could be treated as separate genera. However, since the type of the genus (P. reptans) is in this section, doing so would require either a massive renaming of most Potentilla, or else conserving the type of the genus on a different species. If the latter course were taken, the species in this section would comprise Tormentilla.
Among the distinctive features of sect. Potentilla are the high percentage of stoloniferous species (shared with Duchesnea), a tuberous rootstock in many species, and the presence of tetramerous-flowered species (P. anglica, P. erecta). The section is also distinctive in having an amphi-Atlantic distribution, with native species in both eastern North America and Europe. The native material has sometimes been treated as a single species, or with confused nomenclature (M. L. Fernald 1931), leading to much unreliability in older herbarium annotations.
When leaves are palmate, the lateral leaflet pairs are usually more or less fused at the base, suggesting a ternate origin. Distal cauline leaves and inflorescence bracts are sometimes opposite. For comparison with other sections, counts of cauline leaves are restricted to nodes proximal to the first flowering stolon node, but descriptions of cauline leaves otherwise include all well-developed foliar structures at stolon nodes (until such time as these root and form new basal rosettes).
(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. Flowers 4(–5)-merous; stems usually openly branched; leaflets 3–5; hypanthia 1.5–4 mm diam | → 2 |
1. Flowers 5(–10)-merous; stems not branched; leaflets (3–)5(–7); hypanthia 2.5–7 mm diam | → 3 |
2. Stems soon becoming prostrate, ± flagelliform, eventually rooting at some nodes; inflorescences mostly solitary flowers at stolon nodes; cauline leaves: petioles 0.3–4(–8) cm; basal leaves ± persistent. | P. anglica |
2. Stems mostly ascending to erect, not flagelliform, not rooting at nodes; inflorescences cymose, 3–30-flowered; cauline leaves: petioles usually 0 cm; basal leaves ephemeral. | P. erecta |
3. Petals 7–9(–12) × 6–9(–11) mm; anthers (1–)1.3–2 mm; epicalyx bractlets elliptic or oblong to ovate, 4–10 × 1.5–3.5 mm, often much larger than sepals (especially in fruit); petiole hairs tightly to loosely appressed, 0.5–1.5 mm, leaflet surfaces similar, abaxial green, sparsely to moderately hairy; cauline leaves 2–3(–4) proximal to 1st flowering node; achenes ± rugose; introduced. | P. reptans |
3. Petals 4–7(–8) × 3–6.5(–8) mm; anthers 0.4–1 mm; epicalyx bractlets linear to narrowly lanceolate or lanceolate-elliptic, 2–5(–6) × 0.8–1.5(–2) mm, slightly smaller than to larger than sepals (especially in bud); petiole hairs appressed to spreading, (0.5–)1–3 mm, leaflet surfaces similar to ± dissimilar, abaxial green to silvery white, sparsely to densely hairy; cauline leaves 0–1 proximal to 1st flowering node; achenes smooth or faintly rugose; native | → 4 |
4. Cauline leaves not fully expanded at anthesis, 0–1 proximal to 1st flowering node, leaflets ± resembling those of basal leaves, apex rounded to obtuse, teeth 2–7 per side on distal 1/2 of leaflet; rootstocks erect, stout, 0.5–2 cm. | P. canadensis |
4. Cauline leaves well expanded at anthesis, (0–)1 proximal to 1st flowering node, leaflets often more elongate than those of basal leaves, apex acute to obtuse, teeth 4–8(–13) per side on distal 1/2–3/4 of leaflet; rootstocks horizontal, irregularly thickened or moniliform, 1–8 cm. | P. simplex |
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 |
