| Ranunculaceae | Ranunculus apiifolius Pers. | 2 | ||
| Marsileaceae | Regnellidium diphyllum Lindm. | 2 | OR | |
| Amaryllidaceae | Rhodophiala bifida (Herb.) Traub | 1 | OR | |
| Annonaceae | Rollinia maritima Záchia | 1 | ||
| Dryopteridaceae | Rumohra adiantiformis (G. Forst.) Ching | 1 | M-OR | |
| Alismataceae | Sagittaria montevidensis Cham. & Schltdl. | 2, 4 | M-OR | |
| Salicaceae | Salix humboldtiana Willd. | 1.2 | M-OR-T | |
| Lamiaceae | Salvia guaranitica A. St.-Hil. ex Benth. | 1.2 | ||
| Lamiaceae | Salvia procurrens Benth. | 2 | OR | |
| Salviniaceae | Salvinia sp. | 2 | M | |
| Adoxaceae | Sambucus australis Cham. & Schltdl. | 1 | M | |
| Euphorbiaceae | Sapium glandulosum (L.) Morong | 1, 2, 3 | OR | |
| Anacardiaceae | Schinus engleri F.A. Barkley | 1 | OR | |
| Anacardiaceae | Schinus longifolius (Lindl.) Speg. | 1 | M-OR | |
| Poaceae | Schizachyrium spicatum (Spreng.) Herter | 3 | OR | |
| Cyperaceae | Schoenoplectus americanus (Pers.) Volkart ex Schinz & R. Keller | 2 | OR | |
| Cyperaceae | Schoenoplectus californicus (C.A. Mey.) Soják | 2 | M-OR-Fi | |
| Cyperaceae | Scirpus giganteus Kunth | 2 | OR | |
| Lamiaceae | Scutellaria racemosa Pers. | 2.3 | OR | |
| Rhamnaceae | Scutia buxifolia Reissek | 1.3 | M-OR-T | |
| Euphorbiaceae | Sebastiania brasiliensis Spreng. | 1.2 | M | |
| Euphorbiaceae | Sebastiania commersoniana (Baill.) L.B. Sm. & Downs | 1 | M | |
| Asteraceae | Senecio brasiliensis (Spreng.) Less. | 2.3 | OR | |
| Asteraceae | Senecio crassiflorus (Poir.) DC. | 4 | OR | |
| Asteraceae | Senecio montevidensis (Spreng.) Baker | 1 | OR | |
| Asteraceae | Senecio ostenii Mattf. | 4 | P | OR |
| Asteraceae | Senecio platensis Arechav. | 4 | OR | |
| Asteraceae | Senecio selloi (Spreng.) DC. | 2.4 | OR | |
| Fabaceae | Senna corymbosa (Lam.) H.S. Irwin & Barneby | 1.2 | M-OR | |
| Polypodiaceae | Serpocaulon catharinae (Langsd. & Fisch.) A.R. Sm. | 1 | OR | |
| Fabaceae | Sesbania punicea (Cav.) Benth. | 2 | M-OR | |
| Poaceae | Setaria parviflora (Poir.) Kerguélen | 1.3 | FO-OR | |
| Malvaceae | Sida rhombifolia L. | 2.3 | M-OR | |
| Sapotaceae | Sideroxylon obtusifolium (Roem. & Schult.) T.D. Penn. | 1 | P | M |
| Gesneriaceae | Sinningia allagophylla (Mart.) Wiehler | 1 | OR | |
| Iridaceae | Sisyrinchium platense I.M. Johnst. | 3 | M-OR | |
| Smilacaceae | Smilax campestris Griseb. | 1 | M | |
| Solanaceae | Solanum commersonii Dunal ex Poir. ssp. commersonii | 3 | M-OR |