A key to flowering Didymoplexis in Africa and Madagascar

1a Two or more sepals or petals fused to the mid-point or
more, petals and sepals 11-15 mm
1b Sepals or petals adnate in the basal third or less but none
of them fused to the mid-point, petals and sepals 5-8 mm
2a Lateral sepals fused to the mid-point, other sepal and petals
free to the base or fused to a fifth of their length; column
with short recurved triangular apical arms, broader than
long and acute at the tips; sepals and petals white up to
15 mm long; lip with a low basal bilobed callus and
strongly upcurved sides
Didymoplexis avaratraensis
2b All sepals and petals fused to the mid-point; column lacking
apical arms; sepals and petals white, up to 12 mm long;
lip flabellate, orbicular, distinctly clawed, apex of claw bearing
a reflexed or retrorsely placed ligule-like callus
Didymoplexis africana
3a Column lacking apical arms; lip 3-lobed at the tip, with
two lines of verrucose warts along length; sepals and petals
Didymoplexis verrucosa
3b Column with recurved apical arms that are bilobed at the
tips; lip broadly obovate-spatulate, lacking rows of warts,
with sides only slightly upcurved, and a tall apically
trilobed callus at the base; sepals and petals white, pink or
Didymoplexis recurvata

World Checklist of Monocotyledons. The Board of Trustees of the Royal Botanic Gardens, Kew. Published on the Internet; accessed 28/12/2014

Bibliography and References:
Phillip Cribb, Laurent Gautier & Louis Nusbaumer. How many species are there in the holomycotrophic genus Didymoplexis Griff. (Orchidaceae) in Madagascar?