Key to the species of Nervilia occurring in Africa
All characters used refer to unpollinated flowers in full anthesis (A) and to fully developed and mature leaves (B). Variable species are keyed out in more than one place. The variability of some of the species makes it necessary, in extreme cases, to know both flowering scape and leaf for a certain determination. However, most "single-aspect" specimens (leaf only or flowers only) are easily determinable.
Unfortunately, "geographical characters" have had to be used to separate the leaves of N. pectinata and N. subintegra. Apart from a difference in mean size they are indistinguishable.
Key to flowering specimens of the genus Nervilia

1 Lip with spur 2
  Lip without spur 3
2 Lip white with purple markings; scent of camphor, spur 1.5-3 mm Nervilia pectinata
  Lip mainly lilac, purple or red; scent sweet; spur 3-4.2 mm Nervilia stolziana
3 Flower single 4
  Flowers 2-several 16
4 Lip mainly white, without strong markings, often with yellow central line 5
  Lip with distinct red or purple markings 8
5 Lip ± horizontal, not trumpet-shaped, very obscurely trilobed with entire margin Nervilia subintegra
  Lip erect, trumpet-shaped, distinctly trilobed or with fringed margin 6
6 Lip above covered by short, inflated, club-shaped hairs, flower large, sepals 25-40 mm long, Madagascar only Nervilia leguminosarum
  Lip with much longer, often hairlike outgrowths (seldom glabrous), flower smaller, sepals < 20 mm long 7
7 Lip with a tuft of spaghetti-like outgrowths, flower very small, sepals mostly less than 13 mm long Nervilia petraea
  Lip with thin, hairlike outgrowths (sometimes lacking) and 3 rows of blunt tubercles or elongated, tapering emergences, flower larger, sepals mostly more than 13 mm long Nervilia crociformis
8 Lip side lobes with strong reddish (or greenish) venation, midlobe recurved 9
  Lip side lobes without strong venation, midlobe seldom recurved 11
9 Column 9-13.5 mm, inflorescence normally 1-flowered, sepals reddish Nervilia ballii
  Column 10-25 mm, inflorescence normally several-flowered, sepals reddish or green 10
10 Column 10-15 mm, inflorescence normally 2-12-flowered, sepals green Nervilia bicarinata
  Column 16-25 mm, inflorescence normally 2-3-flowered, sepals reddish Nervilia shirensis
11 Flower cleistogamous Nervilia lilacea
  Flower not cleistogamous 12
12 Lip sidelobes acute, lip glabrous, Madagascar only Nervilia lilacea
  Lip sidelobes rounded, lip glabrous or hairy 13
13 Lip densely or sparsely pubescent, hairs long, Madagascar only Nervilia affinis
  Lip glabrous, sometimes with short papillae on coloured parts, African mainland 14
14 Lip midlobe with erect or rolled-in edges Nervilia adolphi
  Lip midlobe almost flat with convex central ridge 15
15 Lip midlobe (epichile) much longer and wider than hypochile Nervilia fuerstenbergiana
  Lip midlobe (epichile) of approximately the same length and width as hypochile Nervilia lilacea
16 Inflorescence 4-12-flowered 17
  Inflorescence usually 2-3-flowered, ± secund 19
17 Flowers yellow with red veining; column 15-19 mm (lowest flower) Nervilia renschiana
  Flowers yellow-green with purple or green veins; column 7-15 mm 18
18 Column 10-15 mm Nervilia bicarinata
  Column 7-11 mm Nervilia kotschyi
19 Flowers small, column 7-11 mm; sepals < 26 mm Nervilia kotschyi
  Flowers large, column 16-25 mm; sepals > 25 mm Nervilia shirensis

World Checklist of Monocotyledons. The Board of Trustees of the Royal Botanic Gardens, Kew. Published on the Internet; accessed 06/11/2013