7. Drosera rotundifolia Linnaeus, Sp. Pl. 1: 281. 1753.
Roundleaf sundew, droséra à feuilles rondes Roundleaf sundew, droséra à feuilles rondes
Plants forming winter hibernaculae, rosettes (2–)4–10(–15) cm diam.; stem base not bulbous-cormose. Leaves erect to prostrate; stipules adnate to petioles their entire length, 4–6 mm, margins fimbriate along distal 1/2; petiole differentiated from blade, 1.5–5 cm, glandular-pilose; blade suborbiculate, 0.4–1 cm × 5–12 mm, <broader than long, much shorter than petiole>. Inflorescences 2–15(–25)-flowered; scapes 5–35 cm, glabrous. Flowers 4–7 mm diam.; sepals connate basally, oblong, 4–5 × 1.5–2 mm, glabrous; petals white or pink, spatulate, 5–6 × 3 mm. Capsules 5 mm. Seeds light brown, fusiform, 1–1.5 mm, finely and regularly longitudinally striate, <with metallic sheen>. 2n = 20.
Flowering Jun–Sep. Sphagnum bogs, fens, beaver ponds, swamps, peaty gravels, sandy soil, wet sand (for example, disturbed bottoms of old sand pits, emergent sandy shorelines) in the North, lake and stream margins, sphagnous streamheads, and seeps in the South; 0–3000 m; Greenland; St. Pierre and Miquelon; Alta., B.C., Man., N.B., Nfld. and Labr., N.W.T., N.S., Nunavut, Ont., P.E.I., Que., Sask., Yukon; Alaska, Calif., Colo., Conn., Del., D.C., Ga., Idaho, Ill., Ind., Iowa, Ky., Maine, Md., Mass., Mich., Minn., Miss., Mont., N.H., N.J., N.Y., N.C., N.Dak., Ohio, Oreg., Pa., R.I., S.C., Tenn., Vt., Va., Wash., W.Va., Wis.; Eurasia; Pacific Islands (New Guinea).
Drosera rotundifolia was the carnivorous plant most studied by C. Darwin (1875). The species is circumboreal and is widespread across North America, much more common northward and rarer in the South. It is difficult to grow in warmer climates.
M. L. Fernald (1950) recognized forma breviscapa (Regel) Domin, found in the Canadian Maritime Provinces, with scapes 1–4 cm long and 1–3 flowers, and var. comosa Fernald, found from Gaspé County, Quebec, to New England and northern New York, with the parts of the flowers modified to green gland-bearing leaves. Dwarf, few-leaved plants found in Alaska have been called var. gracilis Laested.