Spotted Golden Thistle 
Spotted joe-pyeweed 
Spotted knapweed 
Spotted Knapweed 
Spreading fleabane 
Spring Gold 
Squarrose Knapweed 
Star tickseed 
Starry rosinweed 
Sticky Everlasting 
Sticky Long-Heads 
Stiff cassinia 
Stiff Sunflower 
Stiff-leaved Goldenrod 
Stinknet 
Stinkwort 
Stokes' Aster 
String-of-Pearls 
Striped hawksbeard 
Striped Treasureflower 
Sulfur Cosmos 
Swamp Marigold 
Swamp Sunflower 
Swamp thistle