1. Arethusa bulbosa Linnaeus, Sp. Pl. 2: 950. 1753.
Plants 2–40 cm. Leaves: blade 5–23 cm × 3–12 mm. Inflorescences: floral bracts 2, inconspicuous. Flowers pink to magenta, rarely white or bluish, gaping, large; sepals erect, narrowly oblanceolate to narrowly oblong, 20–55 × 3–9 mm; petals arcuate, 23–49 × 4–10 mm; lip obovate to oblong, arcuate to reflexed near middle, often obscurely 3-lobed, 19–35 ×10–19 mm; disc with crest of yellow lamellae and fleshy processes. Capsules erect, ovoid to ellipsoid, 15–25 mm. 2n = 40.
Flowering Jun--Jul. Sphagnum bogs, coniferous swamps, calcareous treed to open fens, and moist, acid, sandy meadows; 0--1100 m; Man., N.B., Nfld. and Labr. (Nfld.), N.S., Ont., P.E.I., Que., Sask.; Conn., Del., Ind., Maine, Md., Mass., Mich., Minn., N.H., N.J., N.Y., N.C., Ohio, Pa., R.I., S.C., Tenn., Vt., W.Va., Wis.
The occurrence of Arethusa bulbosa in Cook County, Illinois (F. Swink and G. S. Wilhelm 1994), and in Maryland are unconfirmed.