- She wa yan jiu = Chinese herpetological research
- Sibling species of Trigona from Angola (Hymenoptera, Apinae)
- Spixiana. Supplement
- Spolia zeylanica
- Studies in American plants
- Studies in American plants, II
- Studies in American plants, III
- Studies in American plants, VI
- Studies in the palm genus Syagrus Mart
- Studies in the palm genus Syagrus Mart. II
- Supplement to Orchids of Guatemala, and British Honduras
- Syagrus oleracea (Mart.) Becc. and closely related taxa
- Synopsis of Hemichaena, including Berendtiella (Scrophulariaceae)
- Systematics of Acostaea, Condylago and Porroglossum
- Systematics of Brachionidium ; Addenda to Dresslerella, Platystele, and Porroglossum (Orchidaceae)
- Systematics of Dresslerella and Scaphosepalum ; Addenda to Porroglossum
- Systematics of Jostia, Andinia, Barbosella, Barbrodria, Pleurothallis, subgen. Antilla, subgen. Effusia, subgen. Restrepioidia : addenda to Lepanthes, Masdevallia, Paltystele, Pleurothallis, Restrepiopsis, Scaphosepalum and Teagueia
- Systematics of Laccaria (Agaricales) in the continental United States and Canada, with discussions on extralimital taxa and descriptions of extant types
- Systematics of Lepanthopsis, Octomeria subgenus Pleurothallopsis, Restrepiella, Restrepiopsis, Salpistele and Teagueia : addenda to Platystele, Porroglossum and Scaphosepalum
- Systematics of Masdevallia
- Systematics of Myoxanthus : addenda to Platystele, Pleurothallus, subgenus Scopula and Scaphosepalum
- Systematics of Pleurothallis
- Systematics of Pleurothallis : subgen. Pleurothallis, sect. Pleurothallis, subsect. Antenniferae, subsect. Longiracemosae, subsect. Macrophyllae-Racemosae, subsect. Perplexae, subgen. Pseudostelis, subgen. Acuminatia : addenda to Dracula, Lepanthes, Masdevallia and Pleurothallis, miscellaneous new species of Dryadella, Lepanthes and Pleurothallis
- Systematics of Pleurothallis subgenus Ancipitia, subgenus Scopula, and Trisetella ; Addendum to Porroglossum
- Systematics of the Pleurothallidinae