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.
Phenology: Flowering Jun–Jul.
Habitat: Sphagnum bogs, coniferous swamps, calcareous treed to open fens, and moist, acid, sandy meadows
Elevation: 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.