A key to the genus Ancistrochilus Rolfe

1a. Pseudobulbs orbicular, flattened, up to 2•5 cm. diam.; leaves narrowly lanceolate or elliptical-lanceolate, up to 21 cm. long and 3 cm. broad; sepals and petals lanceolate, acuminate, 3•5-4•5 cm. long, white, greenish at base; lip middle lobe 16-25 mm. long, very slender, often more or less recurved, bright purple, side lobes green with brown markings. Ancistrochilus thomsonianus
1b. Pseudobulbs conical or pyriform, up to 5 cm. diam.; leaves lanceolate, elliptical-lanceolate or oblanceolate, up to 40 cm. long and 7•5 cm. broad; sepals broadly lanceolate to oblanceolate, acute or obtuse, 2-3 cm. long; petals oblanceolate, distinctly narrower than the sepals but only slightly shorter; all tepals rose-coloured to mauve, rarely almost white; lip middle lobe 8-12 mm. long, purple with a yellow apex, side lobes green with brown markings Ancistrochilus rothschildianus

World Checklist of Monocotyledons. The Board of Trustees of the Royal Botanic Gardens, Kew. Published on the Internet; http://www.kew.org/wcsp/monocots/ accessed 26/06/2020