Small white American-aster 
Small Woodland Sunflower 
Small Wrinklewort 
Small's Ragwort 
Small-leaf Pussytoes 
Smooth Beggarticks 
Smooth Blue Aster 
Smooth Cassinia 
Smooth Cat's Ear 
Smooth Golden Fleece 
Smooth Hawkweed 
Sneezewort 
Solanecio mannii 
Southern Daisy 
Southern Globe Thistle 
Southern Harebell 
Southern Rockbell 
Southern Sneezeweed 
Spear Thistle 
Spicate Venus'-Looking-Glass 
Spiked lobelia 
Spiked rampion 
Spiny Cocklebur 
Spiny plumeless thistle