| Francis W. Pennell |
Spermatophytes; Scrophulariaceae |
| Ann P. Pinzl |
Spermatophytes |
| Ghillean T. Prance |
Spermatophytes; Chrysobalanaceae; Bryophytes; Lichens |
| Cyrus G. Pringle |
Algae; Bryophytes; Mycology; Spermatophytes |
| Paul L. Redfearn, Jr. |
Bryophytes; Spermatophytes |
| Clyde F. Reed |
Algae; Bryophytes; Pteridophytes; Spermatophytes; Lichens |
| Padre Raulino Reitz |
Spermatophytes |
| Ludwig Riedel |
Spermatophytes |
| Joseph N. Rose |
Algae; Bryophytes; Cactaceae; Ferns; Fungi; Spermatophytes |
| Henry H. Rusby |
Algae; Spermatophytes; Bryophytes; Lichens |
| Per Axel Rydberg |
Algae; Bryophytes; Mycology; Phanerogams; Pteridophytes; Spermatophytes |
| Sergio C. de Sant'Ana |
Spermatophytes |
| Henry P. Sartwell |
Spermatophytes; Cyperaceae; Bryophytes; Algae; Characeae |
| Arthur C. V. Schott |
Algae; Bryophytes; Spermatophytes |
| George W. Scotter |
Spermatophytes; Bryophytes; Lichens |
| John A. Shafer |
Algae; Pteridophytes; Spermatophytes; Mycology; Bryophytes |
| Aaron J. Sharp |
Algae; Bryophytes; Mycology; Spermatophytes |
| Carleton A. Shurtleff |
Spermatophytes |
| Marcos Silveira |
Spermatophytes; Ecology of arborescent bamboos; systematic botany, plant ecology; flora of Southwestern Amazonia |
| John Kunkel Small |
Algae; Bryophytes; Pteridophytes; Spermatophytes; Lichens |
| Lyman B. Smith |
Spermatophytes; Pteridophytes; Lichens |
| Herbert H. Smith |
Spermatophytes; Bryophytes; Lichens |
| Albert C. Smith |
Algae; Spermatophytes; Pteridophytes; Bryophytes; Lichens |
| Richard Spruce |
Bryophytes; Pteridophytes; Spermatophytes; Lichens |
| Howard Stansbury |
Spermatophytes |