Potentilla sect. Graciles

Perennials, ± tufted, not stoloniferous; taproots not fleshy-thickened; vestiture of long, short-crisped, and sometimes cottony(/crisped) hairs, glands absent or sparse to abundant, sometimes red (P. pulcherrima). Stems decumbent to erect, not flagelliform, not rooting at nodes, lateral to persistent basal rosettes, (0.5–)2–7(–10) dm, lengths (1.5–)2–4 times basal leaves. Leaves: basal sometimes 2-ranked; cauline (0–)1–4(–5); primary leaves palmate to subpalmate, sometimes subpinnate (with distal leaflets ± confluent), not flagelliform, 2–40 cm; petiole: long hairs spreading to appressed, weak to stiff, glands absent or sparse to abundant; leaflets 5–9, at tip or on up to distal 1/4(–3/4) of leaf axis, overlapping or not, narrowly oblanceolate, elliptic, or cuneate to obovate, margins flat to ± revolute, distal 1/4 to nearly whole length evenly to unevenly incised 1/4 to nearly to midvein, teeth (1–)2–10(–12) per side, surfaces similar to strongly dissimilar, abaxial green to white, cottony hairs absent or sparse to dense, adaxial green to grayish, sometimes blue-green and glaucous, long hairs mostly weak, sometimes stiff, soft, or absent. Inflorescences (2–)5–50(–70)-flowered, cymose, ± to very open. Pedicels straight in fruit, 0.2–3(–6.5) cm, proximal often much longer than distal. Flowers 5-merous; hypanthium (3–)3.5–6(–8) mm diam.; petals bright yellow, ± obcordate, (3–)4–10(–12) mm, usually longer than sepals, apex retuse; stamens ca. 20; styles subapical, filiform to tapered, papillate-swollen in proximal 1/10–1/3(–2/3), (1–)1.5–3 mm. Achenes smooth.

Distribution

North America, Mexico.

Discussion

Species 7 or more (7 in the flora).

Section Graciles consists primarily of decumbent to erect, palmate-leaved, yellow-petaled perennials that are the most abundant Potentilla in mid-montane western North America. Most of the diversity treated here as five varieties of the most common species, P. gracilis, was divided by P. A. Rydberg (1908d) into 32 species arranged in six of his unranked groups: Candidae, Graciles, Longipedunculatae, Nuttallianae, Pectinisectae, and Permolles. The number of species in sect. Graciles as now defined is problematic. Although understanding of variation in the continental United States has benefited from the biosystematic analyses of J. Clausen et al. (1940), the potential Mexican representatives have not received equivalent attention. It is likely that some Mexican species placed by B. C. Johnston (1985) in sect. Ranunculoides (Th. Wolf) Juzepczuk are better accommodated in sect. Graciles, as already done here with an expanded circumscription of P. townsendii. Potentilla leptophylla Rydberg, the sole representative of group Heptaphyllae Rydberg, probably belongs in this section as well. The relationship of the North American sect. Graciles to the Eurasian sect. Chrysanthae remains to be determined.

The section contains some of the most taxonomically challenging groups among the North American cinquefoils, made all the more complex because its members often hybridize with species within and beyond sect. Graciles. Facultative apomixis is highly probable, resulting in populations of uncertain taxonomic status. The approach used here is to key and describe only the core representatives of the entities treated here, with some of the additional variation accounted for in the discussion.

The circumscriptions adopted here approximate those of J. Clausen et al. (1940), albeit with some species treated as varieties. Because the studies by Clausen et al. were centered in California, variation in the Rocky Mountains, Colorado Plateau, and northern prairies remains poorly analyzed.

Selected References

None.

Lower Taxa

Potentilla bruceae, Potentilla brunnescens, Potentilla drummondii, Potentilla glaucophylla, Potentilla gracilis, Potentilla pulcherrima, Potentilla townsendii

Key

1	Basal leaves subpalmate to pinnate; leaflets on distal 1/10–1/2(–3/4) of leaf axis	> 2
1	Basal leaves palmate, rarely subpalmate; leaflets on tip or less than distal 1/10 of leaf axis	> 5
2	Leaflet surfaces usually strongly dissimilar, abaxial grayish to white, cottony (or crisped-cottony) hairs abundant to dense; mostly Great Basin and east.	Potentilla pulcherrima
2	Leaflet surfaces ± similar, abaxial green or ± blue-green to grayish, cottony hairs usually absent (short-crisped hairs sometimes sparse to common); mostly w, n of the Great Basin	> 3
3	Leaflets usually glaucous, ± blue-green, ± evenly incised on distal 1/3–1/2(–2/3), teeth 1–3(–5) per side; anthers 0.4–0.7(–0.9) mm.	Potentilla glaucophylla
3	Leaflets not glaucous, green to grayish, evenly to unevenly incised on distal 1/2–3/4, teeth (2–)3–7(–8) per side (sometimes secondarily toothed); anthers 0.7–1.2 mm	> 4
4	Leaflets usually gray-green to grayish, long hairs ± abundant, short-crisped hairs usually sparse to common; petioles: long hairs abundant, weak, appressed to ascending-spreading.	Potentilla bruceae
4	Leaflets green, long hairs nearly absent or sparse to common (sometimes restricted to abaxial veins), short and crisped hairs usually absent; petioles: long hairs absent or sparse to abundant, usually stiff, tightly appressed.	Potentilla drummondii
5	Leaflet surfaces usually strongly dissimilar, abaxial grayish to white, not glaucous, cottony (or crisped-cottony) hairs abundant to dense	> 6
5	Leaflet surfaces similar to ± dissimilar, abaxial green, ± blue-green, or pale green to grayish, rarely whitish, sometimes glaucous, crisped hairs sparse or abundant, sometimes absent, cottony hairs usually absent	> 7
6	Glands usually absent or inconspicuous, uncolored; leaflets evenly to unevenly incised 1/4–3/4+ to midvein; styles ± tapered, papillate-swollen proximally.	Potentilla gracilis
6	Glands usually conspicuous, red-tipped; leaflets evenly incised 1/4–1/2 to midvein; styles filiform to tapering above papillate-swollen base.	Potentilla pulcherrima
7	Leaflets usually glaucous, ± blue-green, incised on distal 1/3–1/2(–2/3), teeth 1–3(–5) per side; anthers 0.4–0.7(–0.9) mm; stems 0.5–3(–4.5) dm; inflorescences 2–10(–20)-flowered.	Potentilla glaucophylla
7	Leaflets not glaucous, dark green to grayish, rarely whitish, incised on distal (1/4–)1/2 to nearly whole length, teeth (2–)5–10(–11) per side; anthers (0.5–)0.6–1.2(–1.6) mm; stems (0.5–)2–7(–10) dm; inflorescences (4–)10–50(–70)-flowered	> 8
8	Leaflets narrowly oblanceolate-elliptic, incised 1/4–1/3 to midvein, teeth 1–2 mm, abaxially green, long hairs usually absent or limited to veins and margins, short and crisped hairs absent; Arizona and New Mexico.	Potentilla townsendii
8	Leaflets oblanceolate to elliptic or obovate, incised 1/4–3/4+ to midvein, teeth 2–17(–20) mm, abaxially green or pale green to grayish, rarely whitish, long hairs sparse to abundant, sometimes mostly on veins, short-crisped hairs absent or sparse to abundant; mostly n, w of Arizona and New Mexico	> 9
9	Glands usually absent or inconspicuous, uncolored; leaflets dark green to grayish, rarely whitish; epicalyx bractlets: hairs sparse to abundant, rarely dense, ± appressed to ascending, rarely spreading.	Potentilla gracilis
9	Glands conspicuous, usually golden; leaflets green; epicalyx bractlets: hairs sparse to common, loosely appressed to spreading.	Potentilla brunnescens