Description from Flora of China
Phyllomphax henryi Schlechter, Repert. Spec. Nov. Regni Veg. Beih. 4: 45. 1919; Platanthera dielsiana Soó.
Plants (21-)24-54 cm tall. Tubers oblong, 1.5-2 cm. Stem with several overlapping tubular sheaths at base, densely 4- or 5-leaved above. Leaves oblong-elliptic or sometimes elliptic, 6-15 × 2-4 cm, apex subacute. Inflorescence with 4-10 or more well-spaced flowers; floral bracts ca. as large as leaves or slightly smaller, much longer than flowers. Flowers white or pale purple, rather large; ovary slightly arching toward apex, twisted, cylindric, ca. 1.5 cm including pedicel. Dorsal sepal narrowly ovate-lanceolate, ca. 13 × 5 mm, 5-veined, apex obtuse; lateral sepals similar to dorsal sepal, slightly oblique, ca. 13 × 5 mm, 5-veined. Petals oblique, ovate-lanceolate, ca. 12.5 × 6 mm, 3- or 4-veined, apex obtuse; lip much larger than sepals and petals, suborbicular, 1.5-2.5 × 1.5-2 cm, base spurred, apex entire; spur subcylindric-conic, 6.5-15 mm, apex shallowly 2-lobed and then abruptly contracted, often hooked. Fl. Aug-Sep.
Forests, open grassy slopes; 500-1800(-2300) m. S Guizhou, S and SW Yunnan [Myanmar, Thailand, Vietnam].