Habenaria formosana Schlechter, Repert. Spec. Nov. Regni Veg. Beih. 4: 127. 1919, based on H. tentaculata (Lindley) H. G. Reichenbach var. acutifolia Hayata, J. Coll. Sci. Imp. Univ. Tokyo 30(1): 354. 1911; H. brevicalcarata Fukuyama (1932), not (Hayata) Masamune (1968); Peristylus flagellifer (Makino) Ohwi var. acutifolius (Hayata) Hatusima; P. lacertifer (Lindley) J. J. Smith var. formosanus (Schlechter) S. S. Ying, nom. superfl.

Plants slender, 15-45 cm tall. Tubers subglobose, 1-2 × 0.8-1.5 cm. Stem with 2 or 3 tubular sheaths at base, 3- or 4-leaved. Leaves forming a basal rosette to somewhat spaced along stem, elliptic to ovate-lanceolate, 5-10 × 2-3 cm, apex obtuse or acute. Inflorescence 13-36 cm; peduncle cylindric, slender; sterile bracts 2 or 3, lanceolate, to 1.5 cm; rachis 6-20 cm, densely many flowered; floral bracts ovate-lanceolate, 8-12 mm, basal ones exceeding flowers, apex acuminate. Flowers erect to horizontal, whitish green; ovary 8-10 mm including pedicel. Dorsal sepal erect, ovate, concave, 3.5-4 × 2.2-2.5 mm, apex obtuse-rounded; lateral sepals spreading, oblong-elliptic, 3.8-4.8 × ca. 1.8 mm, apex subobtuse to acute. Petals connivent with dorsal sepal and forming a hood, ovate-rhombic, 3.8-4.8 × ca. 2.5 mm, apex acute; lip narrowly ovate, ca. 4 × 1.8 mm, deeply 3-lobed near base; disk with a large, subglobose callus near base; lateral lobes diverging widely from axis of lip, filiform, 5-12 mm; mid-lobe ligulate, 1.7-3 mm, apex obtuse; spur saccate-ovoid, neck contracted, ca. 2 mm, apex subacute. Column ca. 1.5 mm; viscidia oblong; rostellum with short arms. Fl. Aug-Dec.

"Caeloglossum formosanum" [sic] (Makino & Hayata, J. Coll. Sci. Imp. Univ. Tokyo 22: 420. 1906) belongs here but is a nomen nudum and was therefore not validly published.

The identity and placement of this species within the genus remains contentious. Garay and Sweet (Orchids S. Ryukyu Islands, 37. 1974) considered it conspecific with Habenaria lacertifera, a position followed by Seidenfaden (Dansk Bot. Ark. 31(3): 58. 1977, as Peristylus lacertifer). More recently, however, Su (Fl. Taiwan 5: 994. 2000) maintained the two taxa as distinct on account of differences in lip shape and flower color. A re-assessment of type material and of fresh material is clearly required.

Open places, grasslands; below 300 m. Taiwan [Japan (Ryukyu Islands)].