8. Potentilla erecta (Linnaeus) Raeuschel, Nomencl. Bot. 152. 1797.
Erect cinquefoil, tormentil
Tormentilla erecta Linnaeus, Sp. Pl. 1: 500. 1753
Rootstocks erect to horizontal, irregularly thickened, 1–8 cm. Stems mostly ascending to erect, not flagelliform, openly branched, not rooting at nodes, (0.5–)1–5(–7) dm. Basal leaves ephemeral, usually ternate, 2–15 cm; petiole (1–)3–13 cm, long hairs sparse to common, appressed, 0.5–1 mm, stiff, glands absent; leaflets 3(–5), central ± obovate to cuneate, (0.5–)1–2 × (0.3–)1–1.5 cm, distal 1/2–2/3 of margin incised ± 1/3 to midvein, teeth 2–4 per side, surfaces similar, green (abaxial sometimes paler), glabrate or sparsely to moderately hairy. Cauline leaves (0–)1–3(–7) proximal to 1st flowering node, expanded at anthesis, usually ternate, rarely palmate (or appearing so because of leafletlike stipules), (0.5–)1–3 cm; petiole usually 0 cm; leaflets 3(–5), usually much narrower than those of basal leaves, ˂narrowly cuneate to oblanceolate, (0.5–)1–3 × (0.2–)0.5–1 cm, distal 1/3–2/3 of margin incised ± 1/2 to midvein, teeth 2–4(–6) per side˃, apex usually obtuse to acute. Inflorescences 3–30-flowered, cymose, open. Pedicels (1–)2–3(–5) cm. Flowers 4(–5)-merous; epicalyx bractlets ovate to narrowly elliptic, 1.5–4 × 0.5–1 mm, much smaller than to sometimes equal to sepals; hypanthium 1.5–2.5 mm diam.; sepals (2–)3–5 mm, apex broadly acute; petals (2–)4–6 × (1.5–)3–6 mm, apex ± retuse; stamens 15–20, filaments 2–3.8 mm, anthers 0.4–0.6 mm; carpels 4–8(–20), styles 0.9–1.4 mm. Achenes 1.2–2 mm, rugose. 2n = 28 (Eurasia).
Flowering unknown. Moist, mossy flats and slopes, acidic soil; 0–100 m; introduced; N.S.; Mass.; Europe; w Asia; n Africa; Atlantic Islands (Azores).
Although included here, Potentilla erecta is questionably extant as a naturalized species in North America and is not currently known from Newfoundland where historically reported. It is a medicinal plant called tormentil, high in tannins and strongly astringent. A tea made from the tuberous rootstock is widely used in Europe and parts of Asia for diarrhea, dysentery, sore throats, and related problems. A decoction is a mild antibiotic used for cuts and minor infections, especially as an anti-inflammatory for gingivitis and other gum problems. The rootstock is used as a red dye.
Another synonym with a long history of use is Potentilla tormentilla Necker, illegitimate by virtue of being superfluous.