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FNA | Family List | FNA Vol. 9 | Rosaceae | Potentilla

8p. Potentilla Linnaeus sect. Subviscosae (Rydberg) O. Stevens in N. L. Britton et al., N. Amer. Fl. 22(7): 11. 1959.

Barbara Ertter

Potentilla [unranked] Subviscosae Rydberg, Bull. Torrey Bot. Club 23: 429. 1896

Perennials, rosetted or tufted, not stoloniferous; taproots sometimes ± thickened; vestiture of long and short (rarely short-crisped) hairs, glands sparse to abundant, sometimes red. Stems ± prostrate to decumbent, sometimes pendent (on rock faces), not flagelliform, not rooting at nodes, lateral to persistent basal rosettes, 0.2–2(–3) dm, lengths 1–3(–5) times basal leaves. Leaves: basal not in ranks; cauline 0–2; primary leaves ternate or palmate, (1–)2–10(–18) cm; petiole: long hairs usually spreading to ascending, sometimes loosely appressed, weak to stiff, glands usually abundant, sometimes sparse; leaflets 3–5(–7), at tip of leaf axis, separate to slightly overlapping, oblanceolate or elliptic to broadly obovate or cuneate to flabellate, sometimes nearly orbiculate, margins flat, distal 1/3–3/4 evenly to unevenly (P. subviscosa) incised 1/5–3/4 to midvein, ˂sometimes deeply lobed as well (P. subviscosa)˃, teeth (1–)2–4(–9) per side, surfaces similar, green to gray-green, not glaucous, long hairs weak to stiff, cottony hairs absent. Inflorescences solitary flowers or 2–10(–20)-flowered, usually ± cymose, open, sometimes racemiform when prostrate. Pedicels usually recurved in fruit, 0.5–2(–4) cm, proximal usually not much longer than distal. Flowers 5-merous; hypanthium 2–6 mm diam.; petals pale to bright yellow, narrowly or ± obcordate, rarely broadly obovate, (2–)3–7(–8) mm, longer than sepals, apex usually ± retuse; stamens 15–20; styles subapical, usually filiform, sometimes tapered-columnar (P. cottamii), papillate-swollen in proximal 1/10(–1/3 in P. cottamii), (1–)1.5–2.5(–3) mm. Achenes smooth to ± rugose.

Species ca. 10 (7 in the flora): sw United States, n Mexico.

Section Subviscosae consists of species that have radiated in the sky islands of southwestern North America and Mexico, mostly in rocky meadows or outcrops in forested montane areas (B. Ertter 2007c). Some species are chasmophytic, forming clumps on cliffs or steep rock outcrops, similar to species in Ivesia sect. Setosae. Mexican species are poorly known but include at least Potentilla mexiae Standley and possibly P. rydbergiana Rose, as well as undescribed taxa.

Section Subviscosae shares with sect. Concinnae leaves that are often palmate, prostrate stems, and slender pedicels that become recurved in fruit, as well as a similar biogeographic pattern. Section Subviscosae differs in that cottony and strongly verrucose hairs are lacking, leaves are never strongly bicolored, and petiole and stem hairs are spreading to loosely appressed. Vestiture consists of varying proportions of long hairs, short hairs, and glands; petals are often somewhat clawed, unlike the unclawed norm in the genus.

1 Basal leaves usually ternate, rarely palmate   (2)
+ Basal leaves usually palmate, rarely ternate   (4)
2 (1) Petals (2–)3–4 mm; styles 1–1.5 mm; ne Nevada, nw Utah.   60 Potentilla cottamii
+ Petals 3–8 mm; styles 2–3 mm; se Arizona   (3)
3 (2) Petioles: long hairs 1–2(–3) mm; central leaflets with 2–3(–4) teeth per side; Santa Rita, Huachuca, and Chiricahua ranges.   58 Potentilla rhyolitica
+ Petioles: long hairs 0.5–1(–1.5) mm; central leaflets with 3–5(–6) teeth per side; Pinaleño Mountains, nearby Mogollon Rim, and Santa Catalina Range.   59 Potentilla albiflora
4 (1) Petals nearly white abaxially, pale yellow adaxially, narrowly obcordate; central leaflets evenly to unevenly incised (sometimes deeply lobed as well), teeth 2–9 per side; short hairs well differentiated from long hairs, ± abundant to dense throughout.   54 Potentilla subviscosa
+ Petals ± paler abaxially, bright yellow adaxially, ± obcordate; central leaflets evenly incised, teeth 2–4(–5) per side; short hairs not well differentiated from long hairs, absent or sparse throughout   (5)
5 (4) Plants rooted in ground; leaflets gray-green, long hairs abundant to dense; carpels ca. 20, styles (1.2–)1.5–2 mm; s Sierra Nevada and San Bernardino Mountains, California.   55 Potentilla wheeleri
+ Plants rooted in rock crevices, often on vertical surfaces; leaflets green, long hairs sparse to abundant; carpels 5–15(–20), styles 1.5–2.5 mm; s California, nw Arizona, and Baja California, Mexico   (6)
6 (5) Central leaflets 1–3 cm, oblanceolate to broadly obovate-cuneate or nearly orbiculate, distal ± 1/3 of margins incised ± 1/4 to midvein; epicalyx bractlets lanceolate-elliptic, rarely linear; San Jacinto Mountains, California, and Baja California, Mexico.   56 Potentilla rimicola
+ Central leaflets 0.5–1.5(–2) cm, oblanceolate, distal ± 3/4 of margins incised 1/2–3/4 to midvein; epicalyx bractlets ovate-elliptic; Hualapai Mountains, Arizona.   57 Potentilla demotica


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