Purple foxglove 
Purple Toadflax 
Purslane speedwell 
Red kittentails 
Red Turtlehead 
Ribwort Plantain 
Roundleaf cancerwort 
Sea Plantain 
Sibirian veronicastrum 
Sibthorpia peregrina 
Sicilian Snapdragon 
Sierra beardtongue 
Slender speedwell 
Small-flowered Blue-eyed Mary 
Small-flowered foxglove 
Spanish Peaks Foxglove 
Spiked speedwell 
Straw Foxglove 
Synthyris missurica 
synthyris reniformis 
Syrian Speedwell 
Texas Toadflax 
Three-leaved Toadflax 
Thyme-leaved Speedwell