Common Twayblade

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.

Plants 15-40 (-70) cm tall. Stem glabrous below, downy above. Leaves sessile, in the middle of the stem or slightly below, almost opposite, spreading horizontally, oval to nearly orbicular, with cuspidate apex. Inflorescence ± loosely many-flowered, up to 25 cm, rachis ± pubescent. Bracts minute, 4-5 mm. Sepals ovate, obtuse, 4-5 mm; petals ligulate to linear. Labellum cuneate-ligulate, 2-3 times longer than sepals, apex deeply divided into 2 linear, slightly divergent lobes, sometimes with a small tooth in the sinus, with darker green, nectar secreting furrow along the mid-rib. Column 2-3 mm long. Ovary ± globular, with c. 5 mm long, twisted, ± hairy pedicel.

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.

Distribution: Northern hemisphere (Europe, America, Asia), Mediterranean region, S.W. Asia, Himalaya-mountains. Euro-Sibirian element.

introduced; Ont.; Eurasia.

Fl. Per.: May-June.

Flowering late Jun--Jul.

Moist rich humus, or in disturbed areas; 700--800m.

Ophrys ovata Linnaeus, Sp. Pl. 2: 946. 1753; Diphryllum ovatum (Linnaeus) Kuntze; Distomaea ovata (Linnaeus) Spenner; Epipactis ovata (Linnaeus) Crantz; Helleborine ovata (Linnaeus) F. W. Schmidt; Neottia latifolia Richard; N. ovata (Linnaeus) Bluff & Fingerhut