Plants 20-60 cm. Stem green, stout, succulent, glabrous. Leaves: blade yellow-green to green, ovate-elliptic, 10-17 × 10-12 cm, apex acute. Inflorescences 10-100-flowered, lax to dense, 10-50 cm; floral bracts lanceolate, 3 × 1 mm; peduncle and rachis glandular-pubescent. Flowers yellowish green; pedicels stout, 3-4 mm, slightly glandular-pubescent; sepals and petals projecting forward, connivent, forming hood over column; dorsal sepal ovate, concave, 5-6 × 2-3 mm, apex obtuse; lateral sepals ovate, concave, falcate, 4 × 2-3 mm, apex obtuse; petals linear, concave, 4 × 1 mm, apex obtuse; lip acutely deflexed near base, sessile, linear, apical 1/2 expanded, cleft into bluntly rounded lobes separated by tooth in sinus; disc with longitudinal thickened ridge leading to deflection, 8-10 × 4 mm; column short, 2 × 1.5 mm. Capsules semierect, ellipsoid, 10 × 6 mm. 2n = 32, 34, 35, 36, 37, 38, 40, 42. Flowering late Jun--Jul. Moist rich humus, or in disturbed areas; 700--800 m; introduced; Ont.; Eurasia. Listera ovata is a large, robust, aggressive, and exceedingly common orchid weed found in many kinds of habitat throughout Europe into Siberia and India. It may have the potential to become a weedy orchid in North America just as Epipactis helleborine. Listera ovata was used by Charles Darwin in his investigation and description of the method of cross-fertilization in the genus Listera.
Stout and coarse, 2-6 dm; lvs 5-15 cm, ovate to elliptic, usually shorter than the peduncle; infl elongate, with numerous (ca 25-60+) fls, its axis glandular-puberulent; sep ovate, 4-5 mm; lateral pet linear, 4 mm; lip yellow-green, 7-10 mm, cleft nearly to the middle into slender lobes and with a minute tooth in the sinus, acutely angled downward from the narrow base; column 2 mm; 2n=34-38. Disturbed wet woods; widespread in Eurasia, locally intr. on the Bruce Peninsula of Ont. June, July.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.