Vanilla siamensis Rolfe ex Downie, Bull. Misc. Inform. Kew. 1925: 410. 1925.大香荚兰 da xiang jia lan

Stem to several meters long, with long internodes, with a root and a leaf at each node. Leaves loosely arranged, fleshy; blade elliptic, 14-25 × 6-8(-13) cm, glabrous, base slightly contracted, apex acuminate; petiole robust, 1.5-2.5 cm, broad. Raceme axillary, 7-14 cm, many flowered; floral bracts broadly ovate, 7-8 mm, fleshy; pedicel and ovary ca. 2 cm. Flowers opening ephemerally; sepals and petals yellowish green. Sepals oblong or narrowly ovate, 3.8-4.5 × ca. 1.2 cm, apex rounded and slightly involute. Petals obovate-oblong, ca. 4 × 1-1.3 cm, thinly textured; lip rhombic-obovate, ca. 4 cm, basal half adnate to both sides of column, ± trumpet-shaped, indistinctly 3-lobed; lateral lobes embracing column; mid-lobe undulate at margin, with fimbriate papillae near apex; disk with a cup-shaped, shortly hairy appendage centrally. Column 2-2.6 cm, villous on central surface. Fl. Aug. 2n = 32.

Forests; 800-1200 m. S Yunnan [Thailand].