Description from Flora of China
Serapias helleborine Linnaeus var. palustris Linnaeus, Sp. Pl. 2: 950. 1753; Arthrochilium palustre (Linnaeus) Beck; Helleborine palustris (Linnaeus) Schrank; Limodorum palustre (Linnaeus) Kuntze; S. longifolia Linnaeus.
Plants 25-60 cm tall. Rhizome elongate. Stem glabrous toward base, papillose-pubescent above, with 3 or 4 sheaths toward base. Leaves 7 or 8, spreading, lowest one ovate or ovate-elliptic, 4-5 × 2-2.5 cm, others relatively narrow, ovate-lanceolate, narrowly lanceolate, or linear-lanceolate, 4-16 × 0.6-2.5 cm, glabrous, base amplexicaul, apex acute to acuminate. Rachis 10-20 cm, papillose-pubescent, laxly 6- or more flowered. Flowers spreading, resupinate, yellow-green; sepals flushed chestnut-brown and petals with chestnut-brown venation, lip with yellow marks at base and a white epichile; pedicel and ovary ca. 15 mm, papillose-pubescent. Dorsal sepal elliptic-lanceolate, slightly cymbiform, 8-9 × ca. 2.5 mm, apex acute; lateral sepals ovate-lanceolate, slightly oblique, 7-8 × ca. 4 mm, apex acute and apiculate. Petals elliptic, 7-8 × ca. 3 mm, apex acuminate; lip ca. 10 mm, with a mesochile connecting hypochile and epichile; hypochile cymbiform, ca. 4 × 4-6 mm, with suberect lateral lobes, irregularly papillate inside and slightly carinate; mesochile oblong to subsquare, ca. 2 × 1.5 mm, with a pair of suborbicular lamellae 1-1.5 mm tall that extend onto epichile; epichile oblate to suborbicular, 3-5 × 4-4.5 mm, margin irregularly and inconspicuously crenulate, apex rounded. Column erect, ca. 3 mm; anther elliptic, ca. 3 mm, papillate on dorsal surface. Fl. Jul. 2n = 40, 44, 46, 48.
N Xinjiang [Russia; Europe].