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 
Southwestern mock vervain 
Spanish Peaks Foxglove