Sideritis libanotica 
Sideritis perfoliata 
Sideritis pullulans 
Sideritis romana 
Sieber's Scutellaria 
Sierra beardtongue 
Silky eremophila 
Skyblue Lionface 
Skyflower 
Slender Broomrape 
Slender False Foxglove 
Slender speedwell 
Slender Vervain 
Slender Westringia 
Small Flowered Rhynchoglossum 
Small-flowered Blue-eyed Mary 
Small-flowered foxglove 
Snake Jasmine 
Snakebush 
Solenostemon scutellarioides 
South European flowering ash 
South-Salvia 
Southern Appalachian Beebalm 
Southern Catalpa