Barbara Ertter, James L. Reveal

Potentilla [unranked] Leucophyllae Rydberg, Monogr. N. Amer. Potentilleae, 31. 1898; Potentilla [unranked] Hippianae Rydberg; Potentilla sect. Hippianae (Rydberg) Ertter & Reveal

Perennials, ± tufted, not stoloniferous; taproots not fleshy-thickened; vestiture primarily of long and cottony or sometimes crisped-cottony hairs, glands usually absent or sparse, sometimes common, not red. Stems ascending to erect, not flagelliform, not rooting at nodes, lateral to persistent basal rosettes, (0.3–)1.5–7(–8) dm, lengths (1–)1.5–4(–5) times basal leaves. Leaves: basal not 2-ranked; cauline (0–)1–6+; primary leaves pinnate to subpinnate (with distal leaflets often confluent), 3–45(–50) cm; petiole: long hairs usually ± to tightly appressed, sometimes ascending, usually stiff, sometimes weak, glands absent or sparse or obscured; leaflets (5–)7–15, on distal (1/6–)1/5–2/3 of leaf axis, separate to ± overlapping distally, oblanceolate to narrowly obovate, oblong, or cuneate, margins flat, distal 1/4 to whole length, rarely less, usually ± evenly incised 1/4–1/2 or less to midvein, sometimes entire, teeth (0–)2–18 per side, surfaces similar to strongly dissimilar, abaxial white to ± green, cottony hairs absent or sparse to dense, adaxial green to white, not glaucous, long hairs mostly weak, sometimes stiff. Inflorescences (5–)7–60-flowered, cymose, open. Pedicels straight in fruit, 0.3–3(–6) cm, proximal usually much longer than distal. Flowers 5-merous; hypanthium 2–7 mm diam.; petals yellow, ± obcordate, (3–)4–10 mm, usually longer than sepals, retuse; stamens 20–25; styles subapical, tapered-filiform, papillate-swollen in proximal 1/5 or less, (1–)1.5–3 mm. Achenes smooth to slightly rugose.

Species 4 (4 in the flora): w, c North America.

Section Leucophyllae is an apparent radiation of four species in monsoonal regions of the American Southwest, ranging from the Colorado Plateau, Rocky Mountains, and western Great Plains to the prairies of Canada. The plants share features with sect. Graciles but have consistently pinnate leaves, distal leaflets often decurrent, and petioles commonly densely strigose. Plants are often locally abundant in relatively dry forest openings and open grasslands, tending to be more xeric-tolerant than plants of sect. Graciles.

Descriptions and keys focus on the most distinctive expressions, which are blurred by a propensity for the species to hybridize wherever they grow sympatrically. This is counteracted by at least some level of habitat partitioning; for example, Potentilla hippiana tends to occur on deeper soils and P. crinita on rockier slopes than other species in this section.

As a further complication, key diagnostic characters sometimes sort independently in different parts of the relatively large ranges of the species. The prairie expression described as Potentilla argyrea is particularly problematic, undermining the distinction between P. effusa and P. hippiana in the northern part of their ranges. In the southern Rocky Mountains, the two species are relatively distinct on the basis of correlated vestiture and leaflet toothing. In contrast, the prairie expression combines vestiture closer to P. hippiana with leaflet features of P. effusa. Pending further analysis, B. Boivin (1952) and B. C. Johnston (1980) are followed in retaining this variant in P. hippiana, though without formal taxonomic recognition. Inclusion in P. effusa might prove more justified, as done by J. Soják (2006).

Since Potentilla subjuga (sect. Subjugae) and P. ovina (sect. Multijugae) are sometimes identified as members of sect. Leucophyllae, they are included herein and key out in the third and fifth couplets, respectively.