Broad-leaved twayblade

Epipactis convallarioides Swartz, Kongl. Vetensk. Acad. Nya Handl. 21: 232. 1800; Bifolium convallarioides (Swartz) Nieuwland; Diphryllum convallarioides (Swartz) Kuntze; Listera eschscholziana Chamisso; Ophrys convallarioides (Swartz) W. Wight

Plants 5–37 cm, somewhat stoloniferous. Stems green, succulent, glabrous. Leaves: blade green, broadly ovate to elliptic, oval or suborbiculate, 2–7 × 1.5–5.8 cm, apex obtuse to rarely acute or apiculate. Inflorescences 5–20-flowered, lax, 20–120 mm; floral bracts semitranslucent, rhombic-ovate to lanceolate, 3–5 × 1–2.5 mm, apex acute to acuminate; peduncle and rachis densely whitish glandular-pubescent. Flowers yellowish green, sometimes faintly tinged with purple; pedicels slender, 2.5–7 mm, glandular-pubescent; ovary glandular-pubescent, becoming glabrate as it matures; sepals and petals reflexed away from column and lip; dorsal sepal ovate-lanceolate to elliptic, 4.5–5 × 1.5–2 mm, apex obtuse to acute; lateral sepals lanceolate, falcate, 4.5–5.5 × 1.5–1.8 mm, apex acute to obtuse; petals linear, falcate, 4–5 × 0.8–1 mm; lip cuneate, apex dilated and shallowly notched, lateral lobes rounded, with small tooth in sinus, tapering to short, slender claw, with indistinct triangular tooth on either side of base above claw, 8–13 × 5–7 mm, margins minutely bristly-ciliate; column arcuate, slender, 2.5–3.5(–4) × 1 mm, apex slightly expanded. Capsules ellipsoid, 8 × 5 mm, essentially glabrous. 2n = 36.

Flowering Jun--Sep. Rich humus in open woods to boggy meadows, soil circumneutral or at most only mildly acid, prefers cool soil; widespread across northern part of continent, extending southward only at high elevations; 100--2600 m; St. Pierre and Miquelon; Alta., B.C., N.B., Nfld. and Labr. (Nfld.), N.S., Ont., P.E.I., Que.; Alaska (including Aleutian Islands), Ariz., Calif., Colo., Idaho, Maine, Mich., Minn., Mont., Nev., N.H., N.Y., Oreg., S.Dak., Utah, Vt., Wash., Wis., Wyo.

Listera convallarioides has a relatively large flower compared to most of the other listeras. It crosses with L. auriculata to produce a natural hybrid L. × veltmanii Case, which is discussed under 3. L. auriculata.