1. Column apical stelidia long and distinctly exceeding the column apex …S. fenzliana

1* The apical stelidia of the column either slightly exceeding or being below the column apex …2

2. Labellum base with marsupiform thickening …S. cataractarum

2* Labellum base with a pair of fleshy or keel-like calli …3

3. Plant over 100 cm tall …4

3* Plant up to 60 cm tall …5

4. Leaf sheaths dark-hirsute …S. sessilis

4* Whole stems smooth …S. yauaperyensis

5. Leaf sheaths covered by black, minute hairs, sepals ca. 50 mm long …S. lowii

5* Leaf sheaths green, nearly glabrous, sepals up to 40 mm long …S. decora